Tic-tac-toe

From Rosetta Code
(Redirected from Noughts and crosses)
Task
Tic-tac-toe
You are encouraged to solve this task according to the task description, using any language you may know.
Task

Play a game of tic-tac-toe.

Ensure that legal moves are played and that a winning position is notified.


Tic-tac-toe   is also known as:

  •   noughts and crosses
  •   tic tac toe
  •   tick tack toe
  •   three in a row
  •   tres en rayo       and
  •   Xs  and  Os


See also



11l

Translation of: Python
UInt32 seed = 0
F nonrandom_choice(lst)
   :seed = 1664525 * :seed + 1013904223
   R lst[:seed % UInt32(lst.len)]

V board = Array(‘123456789’)
V wins = ([0, 1, 2], [3, 4, 5], [6, 7, 8],
          [0, 3, 6], [1, 4, 7], [2, 5, 8],
          [0, 4, 8], [2, 4, 6])

F printboard()
   print([0, 3, 6].map(x -> (:board[x .+ 3]).join(‘ ’)).join("\n"))

F score(board = board) -> (Char, [Int])?
   L(w) :wins
      V b = board[w[0]]
      I b C ‘XO’ & all(w.map(i -> @board[i] == @b))
         R (b, w.map(i -> i + 1))
   R N

F finished()
   R all(:board.map(b -> b C ‘XO’))

F space(board = board)
   R board.filter(b -> b !C ‘XO’)

F my_turn(xo, &board)
   V options = space()
   V choice = nonrandom_choice(options)
   board[Int(choice) - 1] = xo
   R choice

F my_better_turn(xo, &board)
   ‘Will return a next winning move or block your winning move if possible’
   V ox = I xo == ‘X’ {Char(‘O’)} E Char(‘X’)
   Int? oneblock
   V options = space(board).map(s -> Int(s) - 1)
   Int choice
   L(chc) options
      V brd = copy(board)
      brd[chc] = xo
      I score(brd) != N
         choice = chc
         L.break
      I oneblock == N
         brd[chc] = ox
         I score(brd) != N
            oneblock = chc
   L.was_no_break
      choice = oneblock ? nonrandom_choice(options)
   board[choice] = xo
   R choice + 1

F your_turn(xo, &board)
   V options = space()
   L
      V choice = input("\nPut your #. in any of these positions: #. ".format(xo, options.join(‘’))).trim((‘ ’, "\t", "\r", "\n"))
      I choice C options
         board[Int(choice) - 1] = xo
         R choice
      print(‘Whoops I don't understand the input’)

F me(xo = Char(‘X’))
   printboard()
   print("\nI go at "my_better_turn(xo, &:board))
   R score()

F you(xo = Char(‘O’))
   printboard()
   print("\nYou went at "my_turn(xo, &:board))
   R score()

L !finished()
   (Char, [Int])? s = me(Char(‘X’))
   I s != N
      printboard()
      print("\n#. wins along #.".format(s[0], s[1]))
      L.break
   I !finished()
      s = you(Char(‘O’))
      I s != N
         printboard()
         print("\n#. wins along #.".format(s[0], s[1]))
         L.break
L.was_no_break
   print("\nA draw")
Output:
1 2 3
4 5 6
7 8 9

I go at 8
1 2 3
4 5 6
7 X 9

You went at 3
1 2 O
4 5 6
7 X 9

I go at 1
X 2 O
4 5 6
7 X 9

You went at 5
X 2 O
4 O 6
7 X 9

I go at 7
X 2 O
4 O 6
X X 9

You went at 9
X 2 O
4 O 6
X X O

I go at 4
X 2 O
X O 6
X X O

X wins along [1, 4, 7]

Ada

with Ada.Text_IO, Ada.Numerics.Discrete_Random;
  -- can play human-human, human-computer, computer-human or computer-computer
  -- the computer isn't very clever: it just chooses a legal random move

procedure Tic_Tac_Toe is

   type The_Range is range 1 .. 3;
   type Board_Type is array (The_Range, The_Range) of Character;

   package Rand is new Ada.Numerics.Discrete_Random(The_Range);
   Gen: Rand.Generator; -- required for the random moves

   procedure Show_Board(Board: Board_Type) is
      use Ada.Text_IO;
   begin
      for Row in The_Range loop
         for Column in The_Range loop
            Put(Board(Row, Column));
         end loop;
         Put_Line("");
      end loop;
      Put_Line("");
   end Show_Board;

   function Find_Winner(Board: Board_Type) return Character is
      -- if 'x' or 'o' wins, it returns that, else it returns ' '

      function Three_Equal(A,B,C: Character) return Boolean is
      begin
         return (A=B) and (A=C);
      end Three_Equal;

   begin -- Find_Winner
      for I in The_Range loop
         if    Three_Equal(Board(I,1), Board(I,2), Board(I,3)) then
            return Board(I,1);
         elsif  Three_Equal(Board(1,I), Board(2,I), Board(3,I)) then
            return Board(1,I);
         end if;
      end loop;
      if Three_Equal(Board(1,1), Board(2,2), Board (3,3)) or
         Three_Equal(Board(3,1), Board(2,2), Board (1,3)) then
         return Board(2,2);
      end if;
      return ' ';
   end Find_Winner;

   procedure Do_Move(Board: in out Board_Type;
                     New_Char: Character; Computer_Move: Boolean) is
      Done: Boolean := False;
      C: Character;
      use Ada.Text_IO;

      procedure Do_C_Move(Board: in out Board_Type; New_Char: Character) is
         Found: Boolean := False;
         X,Y: The_Range;
      begin
         while not Found loop
            X := Rand.Random(Gen);
            Y := Rand.Random(Gen);
            if (Board(X,Y) /= 'x') and  (Board(X,Y) /= 'o') then
               Found := True;
               Board(X,Y) := New_Char;
            end if;
         end loop;
      end Do_C_Move;

   begin
      if Computer_Move then
         Do_C_Move(Board, New_Char);
      else -- read move;
         Put_Line("Choose your move, " & New_Char);
         while not Done loop
            Get(C);
            for Row in The_Range loop
               for Col in The_Range loop
                  if Board(Row, Col) = C then
                     Board(Row, Col) := New_Char;
                     Done := True;
                  end if;
               end loop;
            end loop;
         end loop;
      end if;
   end Do_Move;

   The_Board : Board_Type := (('1','2','3'), ('4','5','6'), ('7','8','9'));
   Cnt_Moves: Natural := 0;
   Players: array(0 .. 1) of Character := ('x', 'o'); -- 'x' begins
   C_Player: array(0 .. 1) of Boolean := (False, False);
   Reply: Character;

begin -- Tic_Tac_Toe

   -- firstly, ask whether the computer shall take over either player
   for I in Players'Range loop
      Ada.Text_IO.Put_Line("Shall " & Players(I) &
                             " be run by the computer? (y=yes)");
      Ada.Text_IO.Get(Reply);
      if Reply='y' or Reply='Y' then
         C_Player(I) := True;
         Ada.Text_IO.Put_Line("Yes!");
      else
         Ada.Text_IO.Put_Line("No!");
      end if;
   end loop;
   Rand.Reset(Gen); -- to initalize the random generator

   -- now run the game
   while (Find_Winner(The_Board) = ' ') and (Cnt_Moves < 9) loop
      Show_Board(The_Board);
      Do_Move(The_Board, Players(Cnt_Moves mod 2), C_Player(Cnt_Moves mod 2));
      Cnt_Moves := Cnt_Moves + 1;
   end loop;
   Ada.Text_IO.Put_Line("This is the end!");

   -- finally, output the outcome
   Show_Board (The_Board);
   if Find_Winner(The_Board) = ' ' then
      Ada.Text_IO.Put_Line("Draw");
   else
      Ada.Text_IO.Put_Line("The winner is: " & Find_Winner(The_Board));
   end if;
end Tic_Tac_Toe;
Output:
> ./tic_tac_toe 
Shall x be run by the computer? (y=yes)
y
Yes!
Shall o be run by the computer? (y=yes)
n
No!
123
456
789

1x3
456
789

Choose your move, o
5
1x3
4o6
789

1x3
xo6
789

Choose your move, o
6
1x3
xoo
789

1xx
xoo
789

Choose your move, o
1
oxx
xoo
789

oxx
xoo
78x

Choose your move, o
7
oxx
xoo
o8x

This is the end!
oxx
xoo
oxx

Draw

> ./tic_tac_toe 
Shall x be run by the computer? (y=yes)
n
No!
Shall o be run by the computer? (y=yes)
y
Yes!
123
456
789

Choose your move, x
6
123
45x
789

123
45x
o89

Choose your move, x
4
123
x5x
o89

123
x5x
o8o

Choose your move, x
8
123
x5x
oxo

o23
x5x
oxo

Choose your move, x
5
This is the end!
o23
xxx
oxo

The winner is: x

ALGOL W

The user can play O, X, both or neither. O goes first whether user or computer controlled.

begin

    string(10) board;

    % initialise the board                                                   %
    procedure initBoard ; board := " 123456789";

    % display the board                                                      %
    procedure showBoard ;
        begin
            s_w := 0;
            write( board(1//1), "|", board(2//1), "|", board(3//1) );
            write( "-+-+-" );
            write( board(4//1), "|", board(5//1), "|", board(6//1) );
            write( "-+-+-" );
            write( board(7//1), "|", board(8//1), "|", board(9//1) )
        end showBoard ;

    % returns true if board pos is free, false otherwise                     %
    logical procedure freeSpace( integer value pos ) ;
        ( board(pos//1) >= "1" and board(pos//1) <= "9" );

    % check for game over                                                    %
    logical procedure gameOver ;
        begin
            logical noMoves;
            noMoves := true;
            for i := 1 until 9 do if noMoves then noMoves := not freeSpace( i );
            noMoves
        end gameOver ;

    % makes the specified winning move or blocks it, if it will win          %
    logical procedure winOrBlock( integer   value pos1, pos2, pos3
                                ; string(1) value searchCharacter
                                ; string(1) value playerCharacter
                                ) ;
        if      board(pos1//1) = searchCharacter
            and board(pos2//1) = searchCharacter
            and freeSpace( pos3 )
        then begin
            board(pos3//1) := playerCharacter;
            true
            end
        else if board(pos1//1) = searchCharacter
            and freeSpace( pos2 )
            and board(pos3//1) = searchCharacter
        then begin
            board(pos2//1) := playerCharacter;
            true
            end
        else if freeSpace( pos1 )
            and board(pos2//1) = searchCharacter
            and board(pos3//1) = searchCharacter
        then begin
            board(pos1//1) := playerCharacter;
            true
            end
        else begin
            false
        end winOrBlock ;

    % makes a winning move or blocks a winning move, if there is one         %
    logical procedure makeOrBlockWinningMove( string(1) value searchCharacter
                                            ; string(1) value playerCharacter
                                            ) ;
        (  winOrBlock( 1, 2, 3, searchCharacter, playerCharacter )
        or winOrBlock( 4, 5, 6, searchCharacter, playerCharacter )
        or winOrBlock( 7, 8, 9, searchCharacter, playerCharacter )
        or winOrBlock( 1, 4, 7, searchCharacter, playerCharacter )
        or winOrBlock( 2, 5, 8, searchCharacter, playerCharacter )
        or winOrBlock( 3, 6, 9, searchCharacter, playerCharacter )
        or winOrBlock( 1, 5, 9, searchCharacter, playerCharacter )
        or winOrBlock( 3, 5, 7, searchCharacter, playerCharacter )
        ) ;

    % makes a move when there isn't an obvious winning/blocking move         %
    procedure move ( string(1) value playerCharacter ) ;
        begin
            logical moved;
            moved := false;
            % try for the centre, a corner or the midle of a line            %
            for pos := 5, 1, 3, 7, 9, 2, 4, 6, 8 do begin
                if not moved and freeSpace( pos ) then begin
                    moved := true;
                    board(pos//1) := playerCharacter
                end
            end
        end move ;

    % gets a move from the user                                              %
    procedure userMove( string(1) value playerCharacter ) ;
        begin
            integer move;
            while
                begin
                    write( "Please enter the move for ", playerCharacter, " " );
                    read( move );
                    ( move < 1 or move > 9 or not freeSpace( move ) )
                end
            do  begin
                write( "Invalid move" )
            end;
            board(move//1) := playerCharacter
        end userMove ;

    % returns true if the three board positions have the player character,   %
    %         false otherwise                                                %
    logical procedure same( integer   value pos1, pos2, pos3
                          ; string(1) value playerCharacter
                          ) ;
        (   board(pos1//1) = playerCharacter
        and board(pos2//1) = playerCharacter
        and board(pos3//1) = playerCharacter
        );

    % returns true if the player has made a winning move, false otherwise    %
    logical procedure playerHasWon( string(1) value playerCharacter ) ;
        (  same( 1, 2, 3, playerCharacter )
        or same( 4, 5, 6, playerCharacter )
        or same( 7, 8, 9, playerCharacter )
        or same( 1, 4, 7, playerCharacter )
        or same( 2, 5, 8, playerCharacter )
        or same( 3, 6, 9, playerCharacter )
        or same( 1, 5, 9, playerCharacter )
        or same( 3, 5, 7, playerCharacter )
        ) ;

    % takes a players turn - either automated or user input                  %
    procedure turn ( string(1) value playerCharacter, otherCharacter
                   ; logical   value playerIsUser
                   ) ;
        begin
            if playerIsUser then userMove( playerCharacter )
            else begin
                write( playerCharacter, " moves..." );
                if  not makeOrBlockWinningMove( playerCharacter, playerCharacter )
                and not makeOrBlockWinningMove( otherCharacter,  playerCharacter )
                then move( playerCharacter )
            end;
            showBoard
        end turn ;

    % asks a question and returns true if the user inputs y/Y,               %
    % false otherwise                                                        %
    logical procedure yes( string(32) value question ) ;
        begin
            string(1) answer;
            write( question );
            read( answer );
            answer = "y" or answer = "Y"
        end yes ;

    % play the game                                                          %
    while
        begin
            string(1)  again;
            string(32) gameResult;
            logical    oIsUser, xIsUser;

            oIsUser := yes( "Do you want to play O? " );
            xIsUser := yes( "Do you want to play X? " );

            gameResult := "it's a draw";
            initBoard;
            showBoard;
            while not gameOver and not playerHasWon( "O" ) and not playerHasWon( "X" ) do begin
                turn( "O", "X", oIsUser );
                if playerHasWon( "O" ) then gameResult := "O wins"
                else if not gameOver then begin
                    turn( "X", "O", xIsUser );
                    if playerHasWon( "X" ) then gameResult := "X wins"
                end
            end ;
            write( gameResult );

            yes( "Play again? " )
        end
    do  begin end

end.
Output:
Do you want to play O?          y
Do you want to play X?          n
1|2|3
-+-+-
4|5|6
-+-+-
7|8|9
Please enter the move for O 5
1|2|3
-+-+-
4|O|6
-+-+-
7|8|9
X moves...
X|2|3
-+-+-
4|O|6
-+-+-
7|8|9
...etc...
Please enter the move for O 8
X|2|O
-+-+-
O|O|X
-+-+-
X|O|9
X moves...
X|X|O
-+-+-
O|O|X
-+-+-
X|O|9
Please enter the move for O 9
X|X|O
-+-+-
O|O|X
-+-+-
X|O|O
it's a draw                     
Play again?                     n

AppleScript

property OMask : missing value
property XMask : missing value
property winningNumbers : {7, 56, 73, 84, 146, 273, 292, 448}
property difficulty : missing value

repeat
   set OMask to 0
   set XMask to 0
   
   if button returned of (display dialog "Who should start?" buttons {"I shoud", "CPU"}) = "CPU" then set OMask to npcGet()
   set difficulty to button returned of (display dialog "Please choose your difficulty" buttons {"Hard", "Normal"})
   
   repeat
       set XMask to XMask + 2 ^ (nGet() - 1)
       if winnerForMask(XMask) or OMask + XMask = 511 then exit repeat
       set OMask to npcGet()
       if winnerForMask(OMask) or OMask + XMask = 511 then exit repeat
   end repeat
   
   if winnerForMask(OMask) then
       set msg to "CPU Wins!"
   else if winnerForMask(XMask) then
       set msg to "You WON!!!"
   else
       set msg to "It's a draw"
   end if
   
   display dialog msg & return & return & drawGrid() & return & return & "Do you want to play again?"
end repeat

on nGet()
   set theMessage to "It's your turn Player 1, please fill in the number for X" & return & return & drawGrid()
   repeat
       set value to text returned of (display dialog theMessage default answer "")
       if (offset of value in "123456789") is not 0 then
           if not positionIsUsed(value as integer) then exit repeat
       end if
   end repeat
   return value as integer
end nGet

on npcGet()
   --first get the free positions
   set freeSpots to {}
   repeat with s from 1 to 9
       if not positionIsUsed(s) then set end of freeSpots to 2 ^ (s - 1)
   end repeat
   --second check if 1 move can make the CPU win
   repeat with spot in freeSpots
       if winnerForMask(OMask + spot) then return OMask + spot
   end repeat
   
   if difficulty is "Hard" and OMask is 0 then
       if XMask = 1 or XMask = 4 then return 2
       if XMask = 64 or XMask = 256 then return 128
   end if
   --third check if a user can make make it win (defensive) place it on position
   repeat with spot in freeSpots
       if winnerForMask(XMask + spot) then return OMask + spot
   end repeat
   
   --fourth check if CPU can win in two moves
   repeat with spot1 in freeSpots
       repeat with spot2 in freeSpots
           if winnerForMask(OMask + spot1 + spot2) then return OMask + spot2
       end repeat
   end repeat
   --fifth check if player can win in two moves
   repeat with spot1 in freeSpots
       repeat with spot2 in reverse of freeSpots
           if winnerForMask(XMask + spot1 + spot2) then return OMask + spot1
       end repeat
   end repeat
   --at last pick a random spot
   if XMask + OMask = 0 and difficulty = "Hard" then return 1
   
   return OMask + (some item of freeSpots)
end npcGet

on winnerForMask(mask)
   repeat with winLine in winningNumbers
       if BWAND(winLine, mask) = contents of winLine then return true
   end repeat
   return false
end winnerForMask

on drawGrid()
   set grid to ""
   repeat with o from 0 to 8
       if BWAND(OMask, 2 ^ o) = 2 ^ o then
           set grid to grid & "O"
       else if BWAND(XMask, 2 ^ o) = 2 ^ o then
           set grid to grid & "X"
       else
           set grid to grid & o + 1
       end if
       if o is in {2, 5} then set grid to grid & return
   end repeat
   return grid
end drawGrid

on positionIsUsed(pos)
   return BWAND(OMask + XMask, 2 ^ (pos - 1)) = 2 ^ (pos - 1)
end positionIsUsed

on BWAND(n1, n2)
   set theResult to 0
   repeat with o from 0 to 8
       if (n1 mod 2) = 1 and (n2 mod 2) = 1 then set theResult to theResult + 2 ^ o
       set {n1, n2} to {n1 div 2, n2 div 2}
   end repeat
   return theResult as integer
end BWAND

AutoHotkey

This program uses a Gui with 9 buttons. Clicking on one will place an X there, disable the button, and cause the program to go somewhere. It plays logically, trying to win, trying to block, or playing randomly in that order.

Gui, Add, Button, x12 y12 w30 h30 vB1 gButtonHandler,
Gui, Add, Button, x52 y12 w30 h30 vB2 gButtonHandler,
Gui, Add, Button, x92 y12 w30 h30 vB3 gButtonHandler,
Gui, Add, Button, x12 y52 w30 h30 vB4 gButtonHandler,
Gui, Add, Button, x52 y52 w30 h30 vB5 gButtonHandler,
Gui, Add, Button, x92 y52 w30 h30 vB6 gButtonHandler,
Gui, Add, Button, x12 y92 w30 h30 vB7 gButtonHandler,
Gui, Add, Button, x52 y92 w30 h30 vB8 gButtonHandler,
Gui, Add, Button, x92 y92 w30 h30 vB9 gButtonHandler,
; Generated using SmartGUI Creator 4.0
Gui, Show, x127 y87 h150 w141, Tic-Tac-Toe
Winning_Moves := "123,456,789,147,258,369,159,357"
Return

ButtonHandler:
    ; Fired whenever the user clicks on an enabled button
    Go(A_GuiControl,"X")
    GoSub MyMove
Return

MyMove: ; Loops through winning moves. First attempts to win, then to block, then a random move
    Went=0
    Loop, parse, Winning_Moves,`,
    {
        Current_Set := A_LoopField
        X:=O:=0
        Loop, parse, Current_Set
        {
            GuiControlGet, Char,,Button%A_LoopField%
            If ( Char = "O" )
                O++
            If ( Char = "X" )
                X++
        }
        If ( O = 2 and X = 0 ) or ( X = 2 and O = 0 ){
            Finish_Line(Current_Set)
            Went = 1
            Break ; out of the Winning_Moves Loop to ensure the computer goes only once
        }
    }
    If (!Went)
        GoSub RandomMove
Return

Go(Control,chr){
    GuiControl,,%Control%, %chr%
    GuiControl,Disable,%Control%
    GoSub, CheckWin
}

CheckWin:
    Loop, parse, Winning_Moves,`,
    {
        Current_Set := A_LoopField
        X:=O:=0
        Loop, parse, Current_Set
        {
            GuiControlGet, Char,,Button%A_LoopField%
            If ( Char = "O" )
                O++
            If ( Char = "X" )
                X++
        }
        If ( O = 3 ){
            Msgbox O Wins!
            GoSub DisableAll
            Break
        }
        If ( X = 3 ){
            MsgBox X Wins!
            GoSub DisableAll
            Break
        }
    }
return

DisableAll:
    Loop, 9
        GuiControl, Disable, Button%A_Index%
return

Finish_Line(Set){ ;   Finish_Line is called when a line exists with 2 of the same character. It goes in the remaining spot, thereby blocking or winning.
    Loop, parse, set
    {
        GuiControlGet, IsEnabled, Enabled, Button%A_LoopField%
        Control=Button%A_LoopField%
        If IsEnabled
            Go(Control,"O")
    }
}

RandomMove:
    Loop{
        Random, rnd, 1, 9
        GuiControlGet, IsEnabled, Enabled, Button%rnd%
        If IsEnabled
        {
            Control=Button%rnd%
            Go(Control,"O")
            Break
        }
    }
return

GuiClose:
ExitApp

AWK

# syntax: GAWK -f TIC-TAC-TOE.AWK
BEGIN {
    move[12] = "3 7 4 6 8"; move[13] = "2 8 6 4 7"; move[14] = "7 3 2 8 6"
    move[16] = "8 2 3 7 4"; move[17] = "4 6 8 2 3"; move[18] = "6 4 7 3 2"
    move[19] = "8 2 3 7 4"; move[23] = "1 9 6 4 8"; move[24] = "1 9 3 7 8"
    move[25] = "8 3 7 4 0"; move[26] = "3 7 1 9 8"; move[27] = "6 4 1 9 8"
    move[28] = "1 9 7 3 4"; move[29] = "4 6 3 7 8"; move[35] = "7 4 6 8 2"
    move[45] = "6 7 3 2 0"; move[56] = "4 7 3 2 8"; move[57] = "3 2 8 4 6"
    move[58] = "2 3 7 4 6"; move[59] = "3 2 8 4 6"
    split("7 4 1 8 5 2 9 6 3",rotate)
    n = split("253 280 457 254 257 350 452 453 570 590",special)
    i = 0
    while (i < 9) { s[++i] = " " }
    print("")
    print("You move first, use the keypad:")
    board = "\n7 * 8 * 9\n*********\n4 * 5 * 6\n*********\n1 * 2 * 3\n\n? "
    printf(board)
}
state < 7 {
    x = $0
    if (s[x] != " ") {
      printf("? ")
      next
    }
    s[x] = "X"
    ++state
    print("")
    if (state > 1) {
      for (i=0; i<r; ++i) { x = rotate[x] }
    }
}
state == 1 {
    for (r=0; x>2 && x!=5; ++r) { x = rotate[x] }
    k = x
    if (x == 5) { d = 1 } else { d = 5 }
}
state == 2 {
    c = 5.5 * (k + x) - 4.5 * abs(k - x)
    split(move[c],t)
    d = t[1]
    e = t[2]
    f = t[3]
    g = t[4]
    h = t[5]
}
state == 3 {
    k = x / 2.
    c = c * 10
    d = f
    if (abs(c-350) == 100) {
      if (x != 9) { d = 10 - x }
      if (int(k) == k) { g = f }
      h = 10 - g
      if (x+0 == e+0) {
        h = g
        g = 9
      }
    }
    else if (x+0 != e+0) {
      d = e
      state = 6
    }
}
state == 4 {
    if (x+0 == g+0) {
      d = h
    }
    else {
      d = g
      state = 6
    }
    x = 6
    for (i=1; i<=n; ++i) {
      b = special[i]
      if (b == 254) { x = 4 }
      if (k+0 == abs(b-c-k)) { state = x }
    }
}
state < 7 {
    if (state != 5) {
      for (i=0; i<4-r; ++i) { d = rotate[d] }
      s[d] = "O"
    }
    for (b=7; b>0; b-=5) {
      printf("%s * %s * %s\n",s[b++],s[b++],s[b])
      if (b > 3) { print("*********") }
    }
    print("")
}
state < 5 {
    printf("? ")
}
state == 5 {
    printf("tie game")
    state = 7
}
state == 6 {
    printf("you lost")
    state = 7
}
state == 7 {
    printf(", play again? ")
    ++state
    next
}
state == 8 {
    if ($1 !~ /^[yY]$/) { exit(0) }
    i = 0
    while (i < 9) { s[++i] = " " }
    printf(board)
    state = 0
}
function abs(x) { if (x >= 0) { return x } else { return -x } }

Bash

Computer is X. Computer randomly goes first. Computer plays a good game, but not a perfect game. It will win when it can and draw when it can not.

It performs a depth-first scan of all following moves. It ignores dumb actions like not winning when either player can.

For each possible move it records if it will win, lose, or something else (like win and draw depending on opponent's move).

If there is a choice of best moves, it picks one at random.

I have not used simple bash code to:

  1. keep it under 100 lines;
  2. to demonstrate usefulness of bash integers;
  3. show-off ANSI ESC sequences;
  4. implement recursion in bash;
  5. demonstrate conditional and alternate execution using && and || with { ...; };
  6. show that you don't always need to use $ to refer to integer variables;
  7. encourage use of [[ ]] instead of [ ] for boolean expressions;
  8. provide examples of pattern matching; and
  9. encourage use of bash for more interesting tasks.
#!/bin/bash
declare -a B=( e e e  e e e  e e e )  # Board

function show(){  # show B - underline first 2 rows; highlight position; number empty positoins
  local -i p POS=${1:-9}; local UL BOLD="\e[1m" GREEN="\e[32m" DIM="\e[2m" OFF="\e[m" ULC="\e[4m"
  for p in 0 1 2 3 4 5 6 7 8; do
    [[ p%3 -eq 0 ]] && printf "  "                             # indent boards
    UL=""; [[ p/3 -lt 2 ]] && UL=$ULC                          # underline first 2 rows
    [[ p -eq POS ]]   && printf "$BOLD$GREEN"                  # bold and colour for this position
    [[ ${B[p]} = e ]] && printf "$UL$DIM%d$OFF" $p || printf "$UL%s$OFF" ${B[p]}  # num or UL
    { [[ p%3 -lt 2 ]] && printf "$UL | $OFF"; } || printf "\n" # underline vertical bars or NL
  done
};

function win(){  # win 'X' 3 return true if X wins after move in position 3
  local ME=$1; local -i p=$2
  [[ ${B[p/3*3]} = $ME && ${B[p/3*3+1]} = $ME && ${B[p/3*3+2]} = $ME ]] && return 0  # row
  [[ ${B[p]}     = $ME && ${B[(p+3)%9]} = $ME && ${B[(p+6)%9]} = $ME ]] && return 0  # col
  [[ ${B[4]} != $ME ]] && return 1                                                   # don't test diags
  [[ p%4 -eq 0 && ${B[0]} = $ME && ${B[8]} = $ME ]] && return 0                      # TL - BR diag
  [[ p%4 -eq 2 || p -eq 4 ]] && [[ ${B[2]} = $ME && ${B[6]} = $ME ]]                 # TR - BL diag
};

function bestMove(){  # return best move or 9 if none possible
  local ME=$1 OP=$2; local -i o s p
  local -ia S=( -9 -9 -9  -9 -9 -9  -9 -9 -9 )  # score board
  local -a SB                                   # save board
  [[ ${B[*]//[!e]} = "" ]] && return 9          # game over
  SB=( ${B[*]} )                                # save Board
  for p in 0 1 2 3 4 5 6 7 8; do                          # for each board position
    [[ ${B[p]} != e ]] && continue                        # skip occupied positions
    B[p]=$ME                                              # occupy position
    win $ME $p && { S[p]=2; B=( ${SB[*]} ); return $p; }  # ME wins so this is best move
    bestMove $OP $ME; o=$?                                # what will opponent do
    [[ o -le 8 ]] && { B[o]=$OP; win $OP $o; s=$?; }      # opponent can make a legal move
    S[p]=${s:-1}                                          # save result of opponent move
    B=( ${SB[*]} )                                        # restore board after each trial run
  done
  local -i best=-1; local -ia MOV=()
  for p in 0 1 2 3 4 5 6 7 8; do                     # find all best moves
    [[ S[p] -lt 0 ]] && continue                     # dont bother with occupied positions
    [[ S[p] -eq S[best] ]] && { MOV+=(p); best=p; }  # add this move to current list
    [[ S[p] -gt S[best] ]] && { MOV=(p); best=p; }   # a better move so scrap list and start again
  done
  return ${MOV[ RANDOM%${#MOV[*]} ]}  # pick one at random
};

function getMove(){  # getMove from opponent
  [[ $ME = X ]] && { bestMove $ME $OP; return $?; }     # pick X move automatically
  read -p "O move: " -n 1; printf "\n"; return $REPLY   # get opponents move
};

function turn(){  # turn starts or continues a game. It is ME's turn
  local -i p; local ME=$1 OP=$2
  getMove; p=$?; [[ p -gt 8 ]] && { printf "Draw!\n"; show; return 1; }  # no move so a draw
  B[p]=$ME; printf "%s moves %d\n" $ME $p                                # mark board
  win $ME $p && { printf "%s wins!\n" $ME; show $p; [[ $ME = X ]] && return 2; return 0; }
  [[ ${B[*]//[!e]} = "" ]] && { printf "Draw!\n"; show; return 1; }      # no move so a draw
  show $p; turn $OP $ME                                                  # opponent moves
};

printf "Bic Bash Bow\n"
show; [[ RANDOM%2 -eq 0 ]] && { turn O X; exit $?; } || turn X O
Output:

(nice ANSI formatting is not shown)

Bic Bash Bow
  0 | 1 | 2
  3 | 4 | 5
  6 | 7 | 8
X moves 1
  0 | X | 2
  3 | 4 | 5
  6 | 7 | 8
O move: 5
O moves 5
  0 | X | 2
  3 | 4 | O
  6 | 7 | 8
X moves 2
  0 | X | X
  3 | 4 | O
  6 | 7 | 8
O move: 0
O moves 0
  O | X | X
  3 | 4 | O
  6 | 7 | 8
X moves 4
  O | X | X
  3 | X | O
  6 | 7 | 8
O move: 6
O moves 6
  O | X | X
  3 | X | O
  O | 7 | 8
X moves 7
X wins!
  O | X | X
  3 | X | O
  O | X | 8

BASIC

BASIC256

# basado en código de Antonio Rodrigo dos Santos Silva (gracias):
# http://statusgear.freeforums.net/thread/17/basic-256-tic-tac-toe

global playerturn$
global endGame$
global space$
global player1Score$
global player2Score$
global invalidMove$
global tecla$
global keyQ$
global keyW$
global keyE$
global keyA$
global keyS$
global keyD$
global keyZ$
global keyX$
global keyC$
global keySpace$
global keyEsc$

keyQ$ = 81
keyW$ = 87
keyE$ = 69
keyA$ = 65
keyS$ = 83
keyD$ = 68
keyZ$ = 90
keyX$ = 88
keyC$ = 67
keySpace$ = 32
keyEsc$ = 16777216

dim space$(9)


subroutine clearGameVars()
  playerturn$ = 1
  invalidMove$ = 0
  endGame$ = 0
  tecla$ = 0

  for t = 0 to space$[?]-1
    space$[t] = 0
  next t
end subroutine

subroutine endGame()
  cls
  print "¡Hasta pronto!..."
  end
end subroutine

subroutine printBoard()
  print "          " + space$[0]+" | "+space$[1]+" | "+space$[2]
  print "          " + "— + — + —"
  print "          " + space$[3]+" | "+space$[4]+" | "+space$[5]
  print "          " + "— + — + —"
  print "          " + space$[6]+" | "+space$[7]+" | "+space$[8]
  print ""
end subroutine

subroutine changePlayer()
  if playerturn$ = 1 then
    playerturn$ = 2
  else
    playerturn$ = 1
  end if
end subroutine

subroutine endMatchWithWinner()
  cls
  call printPlayerScore()
  call printBoard()
  endGame$ = 1

  if playerturn$ = 1 then
    player1Score$ += 1
  else
    player2Score$ += 1
  end if

  print "¡Jugador " + playerturn$ + " gana!" + chr(10)
  print "Pulsa [SPACE] para jugar otra partida"
  print "Pulsa [ESC] para dejar de jugar"
  do
    tecla$ = key
    pause .01
    if tecla$ = keySpace$ then call gamePlay()
    if tecla$ = keyEsc$ then call endGame()
  until false
end subroutine

subroutine endMatchWithoutWinner()
  cls
  call printPlayerScore()
  call printBoard()
  endGame$ = 1

  print "                 Nadie ganó :(                  " + chr(10)
  print " Pulsa [SPACE] para comenzar o [ESC] para salir. "
  do
    tecla$ = key
    pause .01
    if tecla$ = keySpace$ then call gamePlay()
    if tecla$ = keyEsc$ then call endGame()
  until false
end subroutine

subroutine printPlayerScore()
  print "--------------------------------------------"
  print " Jugador #1: " + player1Score$ + " pts"
  print " Jugador #2: " + player2Score$ + " pts"
  print "--------------------------------------------" + chr(10)
end subroutine


subroutine printPlayerMessage()
  print "Jugador: " + playerturn$ + ", elige una casilla, por favor."
end subroutine

subroutine gamePlay()
  call clearGameVars()
  cls
  call printPlayerScore()
  call printBoard()
  call printPlayerMessage()
  while 0 = 0
    invalidMove$ = 0

    if endGame$ = 0 then
      do
        tecla$ = key
        pause .01
        validKeypressed$ = 0
        if tecla$ = keyQ$ or tecla$ = keyW$  or tecla$ = keyE$ or tecla$ = keyA$ or tecla$ = keyS$ or tecla$ = keyD$ or tecla$ = keyZ$ or tecla$ = keyX$ or tecla$ = keyC$ then validKeypressed$ = 1
      until validKeypressed$ = 1
    endif

    if tecla$ = keyQ$ then
      if space$[0] = 0 then
        space$[0] = playerturn$
      else
        invalidMove$ = 1
      endif
    endif

    if tecla$ = keyW$ then
      if space$[1] = 0 then
        space$[1] = playerturn$
      else
        invalidMove$ = 1
      endif
    endif

    if tecla$ = keyE$ then
      if space$[2] = 0 then
        space$[2] = playerturn$
      else
        invalidMove$ = 1
      endif
    endif

    if tecla$ = keyA$ then
      if space$[3] = 0 then
        space$[3] = playerturn$
      else
        invalidMove$ = 1
      endif
    endif

    if tecla$ = keyS$ then
      if space$[4] = 0 then
        space$[4] = playerturn$
      else
        invalidMove$ = 1
      endif
    endif

    if tecla$ = keyD$ then
      if space$[5] = 0 then
        space$[5] = playerturn$
      else
        invalidMove$ = 1
      endif
    endif

    if tecla$ = keyZ$ then
      if space$[6] = 0 then
        space$[6] = playerturn$
      else
        invalidMove$ = 1
      endif
    endif

    if tecla$ = keyX$ then
      if space$[7] = 0 then
        space$[7] = playerturn$
      else
        invalidMove$ = 1
      endif
    endif

    if tecla$ = keyC$ then
      if space$[8] = 0 then
        space$[8] = playerturn$
      else
        invalidMove$ = 1
      endif
    endif

    if invalidMove$ = 0 then
      tecla$ = 0

      if space$[0] = 1 and space$[1] = 1 and space$[2] = 1 then call endMatchWithWinner()
      if space$[3] = 1 and space$[4] = 1 and space$[5] = 1 then call endMatchWithWinner()
      if space$[6] = 1 and space$[7] = 1 and space$[8] = 1 then call endMatchWithWinner()
      if space$[0] = 1 and space$[3] = 1 and space$[6] = 1 then call endMatchWithWinner()
      if space$[1] = 1 and space$[4] = 1 and space$[7] = 1 then call endMatchWithWinner()
      if space$[2] = 1 and space$[5] = 1 and space$[8] = 1 then call endMatchWithWinner()
      if space$[0] = 1 and space$[4] = 1 and space$[8] = 1 then call endMatchWithWinner()
      if space$[2] = 1 and space$[4] = 1 and space$[6] = 1 then call endMatchWithWinner()
      if space$[0] = 2 and space$[1] = 2 and space$[2] = 2 then call endMatchWithWinner()
      if space$[3] = 2 and space$[4] = 2 and space$[5] = 2 then call endMatchWithWinner()
      if space$[6] = 2 and space$[7] = 2 and space$[8] = 2 then call endMatchWithWinner()
      if space$[0] = 2 and space$[3] = 2 and space$[6] = 2 then call endMatchWithWinner()
      if space$[1] = 2 and space$[4] = 2 and space$[7] = 2 then call endMatchWithWinner()
      if space$[2] = 2 and space$[5] = 2 and space$[8] = 2 then call endMatchWithWinner()
      if space$[0] = 2 and space$[4] = 2 and space$[8] = 2 then call endMatchWithWinner()
      if space$[2] = 2 and space$[4] = 2 and space$[6] = 2 then call endMatchWithWinner()

      if space$[0] <> 0 and space$[1] <> 0 and space$[2] <> 0 and space$[3] <> 0 and space$[4] <> 0 and space$[5] <> 0 and space$[6] <> 0 and space$[7] <> 0 and space$[8] <> 0 then call endMatchWithoutWinner()

      call changePlayer()
      cls
      call printPlayerScore()
      call printBoard()
      call printPlayerMessage()
    end if

  end while
end subroutine

subroutine gameMenu()
  cls
  call clearGameVars()

  player1Score$ = 0
  player2Score$ = 0

  print "================================================="
  print "|                  TIC-TAC-TOE                  |"
  print "=================================================" + chr(10)
  print "  Teclas para jugar:"
  print "---------------------"
  print "    | q | w | e |"
  print "    | a | s | d |"
  print "    | z | x | c |" + chr(10)
  print " Pulsa [SPACE] para comenzar o [ESC] para salir. "
  
  do
    tecla$ = key
    pause .01
    if tecla$ = keySpace$ then call gamePlay()
    if tecla$ = keyEsc$ then call endGame()
  until false
end subroutine

call gameMenu()
end

FreeBASIC

graphics mode

'About 400 lines of code, but it is a graphical (GUI ish) i.e. mouse driven.
'I have made provision for the player to beat the computer now and then.

Type box
    As long x,y           
    As long wide,high,index
    Dim As ulong colour
    As String caption
    Declare Sub show       
    Declare Sub NewCaption(s As String)
    Declare Constructor
    Declare Constructor(x As long,y As long,wide As long,_
    high As long,index As long,colour As ulong,caption As String)
End Type
Constructor box
End Constructor
Constructor box(x As long,y As long,wide As long,_
high As long,index As long,colour As ulong,caption As String)
this.x=x
this.y=y
this.wide=wide
this.high=high
this.index=index
this.colour=colour
this.caption=caption
End Constructor
'ALL PROCEDURES:
Declare Function inside(B As box,px As long,py As long) As long
Declare Sub make_frame_image(im As ulong Pointer)
Declare Sub setup_grid(boxes() As box,cellsacross As long,cellsdown As long,xp As long,yp As long,w As long,h As long)
Declare Function all_clicked(b() As box) As long
Declare Sub OnCLICK(a() As box,b As box)
Declare Sub refresh_screen(b() As box,f1 As long=0,f2 As long=0)
Declare Function Get_Mouse_Events(boxes() As box) As long
Declare Sub thickline(x1 As long,y1 As long,x2 As long,y2 As long,thickness As Single,colour As ulong,im As Any Pointer=0)
Declare Sub lineto(x1 As long,y1 As long,x2 As long,y2 As long,l As long,th As Single,col As ulong,im As Any Pointer=0)
Declare Sub thickcircle(x As long,y As long,rad As long,th As Single,col As ulong,im As Any Pointer=0)
Declare Sub startup(b() As box)
Declare Sub get_computer_events(b() As box)

Declare Sub finish
'Macro used by more than one procedure
#macro incircle(cx,cy,radius,x,y)
(cx-x)*(cx-x) +(cy-y)*(cy-y)<= radius*radius
#endmacro
'===============  RUN  ============================
Screen 19,32',1,16
Color ,Rgb(233,236,216)              'background colour
windowtitle string(100," ")+"Noughts and crosses"
'Globals:
Dim Shared As ulong Pointer frame
Dim Shared As long computer,player
Dim Shared As String msg1,msg2,message
message="In Play"
msg1="Computer Start"
msg2="Player Start"
'Custom Frame
frame=Imagecreate(800,600)

Dim  As box boxes(0 To 9)

setup_grid(boxes(),3,3,175,85,150,150)
make_frame_image(frame)

Do
    If player=0 And computer=0 Then
        startup(boxes())
    End If
   
    If player  Then
        Get_Mouse_Events(boxes())
    End If
   
    If computer Then
        get_computer_events(boxes())
    End If
   
    If all_clicked(boxes()) Then get_computer_events(boxes())
Loop Until Inkey=Chr(27)
finish

Sub box.show
    Line(this.x,this.y)-(this.x+this.wide,this.y+this.high),this.colour,bf
    Line(this.x,this.y)-(this.x+this.wide,this.y+this.high),Rgb(200,200,200),b
    ''Draw String(this.x+.5*this.wide-4*Len(this.caption),this.y+(.5*this.high-4)),this.caption,Rgb(0,0,0)
    If this.index=0 Then
        Draw String(this.x+.5*this.wide-4*Len(this.caption),this.y+.5*this.high-6),this.caption,Rgb(0,0,0)
    End If
End Sub

Sub box.NewCaption(s As String)
    Var cx=(this.x+this.x+this.wide)/2
    Var cy=(this.y+this.y+this.high)/2
    If s="X" Then
        For k As long=20 To 0 Step -1
            lineto(cx,cy,this.x,this.y,50,k,Rgb(50+10*k,5*k,0),frame)
            lineto(cx,cy,this.x+this.wide,this.y+this.high,50,k,Rgb(50+10*k,5*k,0),frame)
            lineto(cx,cy,this.x,this.y+this.high,50,k,Rgb(50+10*k,5*k,0),frame)
            lineto(cx,cy,this.x+this.wide,this.y,50,k,Rgb(50+10*k,5*k,0),frame)
        Next k
    Else
        For k As long=20 To 0 Step -1
            thickcircle(cx,cy,40,k,Rgb(50+10*k,5*k,0),frame)
        Next k
    End If
End Sub

Sub get_computer_events(b() As box)
    #define other(n)  b(n).caption<>"0" And b(n).caption<>"C"
    #define another(n) b(n).caption="0"
    #define rr(f,l) (Rnd*((l)-(f))+(f))
    Dim As long flag,i,k,Cwin,Pwin,NoWin
    Static As long firstclick
    var chance="001100"
    dim as long ch
    'horiz player finish
    For x As long=1 To 3
        If b(1+k).caption="0" And b(2+k).caption="0" And another((3+k)) Then b(3+k).Caption="0":Pwin=1:Goto fin
        If b(2+k).caption="0" And b(3+k).caption="0" And another((1+k))Then b(1+k).Caption="0":Pwin=1=1:Goto fin
        If b(1+k).caption="0" And b(3+k).caption="0" And another((2+k))Then b(2+k).Caption="0":Pwin=1:Goto fin
        k=k+3
    Next x
    k=0
    'vert player finish
    For x As long=1 To 3
        If b(1+k).caption="0" And b(4+k).caption="0" And another((7+k)) Then b(7+k).Caption="0":Pwin=1:Goto fin
        If b(4+k).caption="0" And b(7+k).caption="0" And another((1+k))Then b(1+k).Caption="0":Pwin=1:Goto fin
        If b(1+k).caption="0" And b(7+k).caption="0" And another((4+k))Then b(4+k).Caption="0":Pwin=1:Goto fin
        k=k+1
    Next x
    k=0
    'player finish main diag
    If b(1+k).caption="0" And b(5+k).caption="0" And another((9+k)) Then b(9+k).Caption="0":Pwin=1:Goto fin
    If b(1+k).caption="0" And b(9+k).caption="0" And another((5+k))Then b(5+k).Caption="0":Pwin=1:Goto fin
    If b(5+k).caption="0" And b(9+k).caption="0" And another((1+k))Then b(1+k).Caption="0":Pwin=1:Goto fin
    'player finish other diag
    If b(7+k).caption="0" And b(5+k).caption="0" And another((3+k)) Then b(3+k).Caption="0":Pwin=1:Goto fin
    If b(5+k).caption="0" And b(3+k).caption="0" And another((7+k))Then b(7+k).Caption="0":Pwin=1:Goto fin
    If b(7+k).caption="0" And b(3+k).caption="0" And another((5+k))Then b(5+k).Caption="0":Pwin=1:Goto fin
   
    'horiz computer finish
    For x As long=1 To 3
        If b(1+k).caption="C" And b(2+k).caption="C" And other((3+k)) Then b(3+k).Caption="C":Cwin=1:Goto fin
        If b(2+k).caption="C" And b(3+k).caption="C" And other((1+k))Then b(1+k).Caption="C":Cwin=1:Goto fin
        If b(1+k).caption="C" And b(3+k).caption="C" And other((2+k))Then b(2+k).Caption="C":Cwin=1:Goto fin
        k=k+3
    Next x
    k=0
    'vert computer finish
    For x As long=1 To 3
        If b(1+k).caption="C" And b(4+k).caption="C" And other((7+k)) Then b(7+k).Caption="C":Cwin=1:Goto fin
        If b(4+k).caption="C" And b(7+k).caption="C" And other((1+k))Then b(1+k).Caption="C":Cwin=1:Goto fin
        If b(1+k).caption="C" And b(7+k).caption="C" And other((4+k))Then b(4+k).Caption="C":Cwin=1:Goto fin
        k=k+1
    Next x
    k=0
    'computer finish main diag
    If b(1+k).caption="C" And b(5+k).caption="C" And other((9+k)) Then b(9+k).Caption="C":Cwin=1:Goto fin
    If b(1+k).caption="C" And b(9+k).caption="C" And other((5+k))Then b(5+k).Caption="C":Cwin=1:Goto fin
    If b(5+k).caption="C" And b(9+k).caption="C" And other((1+k))Then b(1+k).Caption="C":Cwin=1:Goto fin
    'computer finish other diag
    If b(7+k).caption="C" And b(5+k).caption="C" And other((3+k)) Then b(3+k).Caption="C":Cwin=1:Goto fin
    If b(5+k).caption="C" And b(3+k).caption="C" And other((7+k))Then b(7+k).Caption="C":Cwin=1:Goto fin
    If b(7+k).caption="C" And b(3+k).caption="C" And other((5+k))Then b(5+k).Caption="C":Cwin=1:Goto fin
   
    'block horizontals
    For x As long=1 To 3
        If b(1+k).caption="0" And b(2+k).caption="0" And other((3+k)) Then b(3+k).Caption="C":flag=1:Goto fin
        If b(2+k).caption="0" And b(3+k).caption="0" And other((1+k))Then b(1+k).Caption="C":flag=1:Goto fin
        If b(1+k).caption="0" And b(3+k).caption="0" And other((2+k))Then b(2+k).Caption="C":flag=1:Goto fin
        k=k+3
    Next x
    k=0
    'block verticals
    For x As long=1 To 3
        If b(1+k).caption="0" And b(4+k).caption="0" And other((7+k)) Then b(7+k).Caption="C":flag=1:Goto fin
        If b(4+k).caption="0" And b(7+k).caption="0" And other((1+k))Then b(1+k).Caption="C":flag=1:Goto fin
        If b(1+k).caption="0" And b(7+k).caption="0" And other((4+k))Then b(4+k).Caption="C":flag=1:Goto fin
        k=k+1
    Next x
    k=0
    'block main diag
    If b(1+k).caption="0" And b(5+k).caption="0" And other((9+k)) Then b(9+k).Caption="C":flag=1:Goto fin
    If b(1+k).caption="0" And b(9+k).caption="0" And other((5+k))Then b(5+k).Caption="C":flag=1:Goto fin
    If b(5+k).caption="0" And b(9+k).caption="0" And other((1+k))Then b(1+k).Caption="C":flag=1:Goto fin
    'block other diag
    If b(7+k).caption="0" And b(5+k).caption="0" And other((3+k)) Then b(3+k).Caption="C":flag=1:Goto fin
    If b(5+k).caption="0" And b(3+k).caption="0" And other((7+k))Then b(7+k).Caption="C":flag=1:Goto fin
    If b(7+k).caption="0" And b(3+k).caption="0" And other((5+k))Then b(5+k).Caption="C":flag=1:Goto fin
   
    If firstclick=0 Then
        firstclick=1
       var st="1379"
       dim as long i=rr(0,3)
    If Valint(b(5).caption)=0  and b(5).caption <> "C" Then b(st[i]-48).caption="C":Goto fin
       
    End If
   
     ch=rr(0,5)
    if chance[ch]-48=1 then
    If Valint(b(5).caption)<>0 Then b(5).caption="C":Goto fin
    end if
    If all_clicked(b()) Then Nowin=1:Goto fin
    If flag=0 Then
        Randomize
        Do
            i=rr(1,9)
            If Valint(b(i).caption) <> 0  Then b(i).caption="C":Exit Do
        Loop 
    End If
    fin:
    If Cwin=1 Or Pwin=1 Or NoWin=1 Then
        Dim As long mx,my,mb
        dim as integer x,y
        screencontrol 0,x,y
        for z as single=0 to 8*atn(1) step .001
            dim as integer xx=x+100*cos(z)
            dim as integer yy=y+100*sin(z)
            screencontrol 100,xx,yy
        next z
        screencontrol 100,x,y
        If Cwin=1 Then Message="You Loose"
        If Pwin=1 Then Message="You WIN"
        If Nowin=1 Then Message="DRAW"
        
        cwin=0:k=0:pWin=0:Nowin=0:firstclick=0'i
        Do
            Getmouse mx,my,,mb
            If inside(b(0),mx,my) And mb=1 Then finish
          
            Var ic=incircle(500,55,20,mx,my)
            If incircle(500,55,20,mx,my) And mb=1 Then Exit Do
            refresh_screen(b(),ic)
        Loop Until Inkey=chr(27)
        For z As long=1 To Ubound(b)
            b(z).caption=Str(b(z).index)
        Next z
        Imagedestroy frame
        frame=Imagecreate(800,600)
        make_frame_image(frame)
        computer=0:player=0
        Exit Sub
    End If
    player=1:computer=0
End Sub

Sub startup(b() As box)
    message="In Play"
    Dim As long mx,my,mb
    Getmouse mx,my,,mb
   
    For n As long=0 To Ubound(b)
        If inside(b(n),mx,my) And mb=1 Then
            If b(n).index=0 Then
                finish
            End If
        End If
        b(0).colour=Rgb(200,0,0)
    Next n
    Dim As long f1,f2
    If incircle(80,230,10,mx,my) Then
        f1=1:f2=0
        If mb=1 Then computer=1:player=0
    End If
    If incircle(670,230,10,mx,my) Then
        f1=0:f2=1
        If mb=1 Then player=1:computer=0
    End If
    refresh_screen(b(),f1,f2)
End Sub

Sub thickcircle(x As long,y As long,rad As long,th As Single,col As ulong,im As Any Pointer=0)
    Circle(x,y),rad+th/2,col
    Circle(x,y),rad-th/2,col
    Paint(x,y+rad),col,col
End Sub

Sub thickline(x1 As long,_
    y1 As long,_
    x2 As long,_
    y2 As long,_
    thickness As Single,_
    colour As ulong,_
    im As Any Pointer=0)
    Dim p As ulong=Rgb(255, 255, 255)
    If thickness<2 Then
        Line(x1,y1)-(x2,y2),colour
    Else               
        Dim As Double s,h,c
        h=Sqr((x2-x1)^2+(y2-y1)^2) 
        If h=0 Then h=1e-6
        s=(y1-y2)/h               
        c=(x2-x1)/h                 
        For x As long=1 To 2
            Line im,(x1+s*thickness/2,y1+c*thickness/2)-(x2+s*thickness/2,y2+c*thickness/2),p
            Line im,(x1-s*thickness/2,y1-c*thickness/2)-(x2-s*thickness/2,y2-c*thickness/2),p
            Line im,(x1+s*thickness/2,y1+c*thickness/2)-(x1-s*thickness/2,y1-c*thickness/2),p
            Line im,(x2+s*thickness/2,y2+c*thickness/2)-(x2-s*thickness/2,y2-c*thickness/2),p
            Paint im,((x1+x2)/2, (y1+y2)/2), p, p
            p=colour
        Next x
    End If
End Sub

Sub lineto(x1 As long,y1 As long,x2 As long,y2 As long,l As long,th As Single,col As ulong,im As Any Pointer=0)
    Dim As long diffx=x2-x1,diffy=y2-y1,ln=Sqr(diffx*diffx+diffy*diffy)
    Dim As Single nx=diffx/ln,ny=diffy/ln
    thickline(x1,y1,(x1+l*nx),(y1+l*ny),th,col,im)
End Sub

Function inside(B As box,px As long,py As long) As long
    Return (px>B.x)*(px<(B.x+B.wide))*(py>B.y)*(py<(B.y+B.high))
End Function
Sub make_frame_image(im As ulong Pointer)
    #macro map(a,b,x,d,c)
    ((d)-(c))*((x)-(a))/((b)-(a))+(c)
    #endmacro
    #macro logo(sx,sy,rad)
For k As Single=-rad/10 To rad/10 Step .5:Circle im,(sx,sy),rad+k,Rgb(15,118,155):Next
For k As Single=-rad/10 To rad/10 Step .5:Circle im,(sx+1.3*rad,sy+rad),rad+k,Rgb(230,193,78),2.,1.7:Next
For k As Single=-rad/10 To rad/10 Step .5:Circle im,(sx+2*1.3*rad,sy),rad+k,Rgb(21,3,0),3.25,3.05:Next
For k As Single=-rad/10 To rad/10 Step .5:Circle im,(sx+3*1.3*rad,sy+rad),rad+k,Rgb(26,143,76),2,1.8:Next
For k As Single=-rad/10 To rad/10 Step .5:Circle im,(sx+4*1.3*rad,sy),rad+k,Rgb(200,63,87),3.25,3.05:Next
#endmacro
    For k As long=0 To 50
        Var r=map(0,50,k,233,193-20)
        Var g=map(0,50,k,236,153-20)
        Var b=map(0,50,k,216,19-19)
        Line im,(0+k,20+k)-(800-k,600-k),Rgb(r,g,b),b
    Next k
    For k As long=0 To 20
        Var r=map(0,20,k,250,0)
        Var g=map(0,20,k,250,0)
        Var b=map(0,20,k,250,255)
        Line im,(0,k)-(780,k),Rgb(r,g,b)',bf
    Next k
    logo(60,8,5)
    logo(380,8,5)
    logo(720,8,5)
End Sub
Sub setup_grid(boxes() As box,cellsacross As long,cellsdown As long,xp As long,yp As long,w As long,h As long)
    Dim As long index
    For y As long=yp To yp+h*(cellsdown-1) Step h
        For x As long=xp To xp+w*(cellsacross-1)   Step w
            index=index+1
            boxes(index)=Type<box>(x,y,w,h,index,Rgb(133,136,116),Str(index))
        Next x
    Next y
    boxes(0)=Type<box>(780,-2,20,24,0,Rgb(200,0,0),"X")
End Sub

Function all_clicked(b() As box) As long
    Dim As long sum
    For z As long=1 To Ubound(b)
        sum=sum+Valint(b(z).caption)
    Next z
    If sum<=0 Then Return -1
End Function

Sub OnCLICK(a() As box,b As box)
    If b.caption="0" Then Exit Sub
    If b.caption="C" Then Exit Sub
    If b.caption <> "C" Then b.caption="0"
    If b.index=0 Then finish
    player=0:computer=1
End Sub

Sub refresh_screen(b() As box,f1 As long=0,f2 As long=0)
    Screenlock:Cls
    For n As long=0 To Ubound(b)
        b(n).show 'draw boxes
        If b(n).caption="0" Then b(n).NewCaption("X")
        If b(n).caption="C" Then b(n).NewCaption("O")
    Next n
    Put(0,0),frame,trans
    Draw String (390,50),message,Rgb(0,0,0)
    If message <>"In Play" Then
        Circle(500,55),20,Rgb(255,20,255),,,,f
        If f1=-1 Then Circle(500,55),20,Rgb(202,200,200),,,,f
        Draw String(480,50),"Click",Rgb(0,0,0)
    End If
    If computer=0 And player=0 Then
        Draw String (60,200),msg1,Rgb(0,0,0)
        Circle(80,230),10,Rgb(0,0,0)
        Circle(80,230),5,Rgb(100,100,100),,,,f
        If f1=1 Then Circle(80,230),10,Rgb(200,0,0),,,,f
        Draw String (650,200),msg2,Rgb(0,0,0)
        Circle(670,230),10,Rgb(0,0,0)
        Circle(670,230),5,Rgb(100,100,100),,,,f
        If f2=1 Then Circle(670,230),10,Rgb(200,0,0),,,,f
    End If
    Screenunlock:Sleep 1,1
End Sub

Function Get_Mouse_Events(boxes() As box) As long
    Static released As long
    Static pressed As long
    Dim As long mousex,mousey,mousebutton ,x,y
    Getmouse mousex,mousey,,mousebutton
    Dim As box bar=Type<box>(0,0,780,50,0,0,"")
   
    refresh_screen(boxes())
    For n As long=0 To Ubound(boxes)
        If inside(boxes(n),mousex,mousey)  Then
            If released Then
                boxes(n).colour=Rgb(120,123,103) 
                If n=0 Then boxes(0).colour=Rgb(255,0,0)
            End If
            If mousebutton=1 Then
                If released Then OnCLICK(boxes(),boxes(n))
                Exit For
            End If
        Else
            boxes(n).colour=Rgb(133,136,116)
            If n=0 Then boxes(0).colour=Rgb(200,0,0)
        End If
    Next n
    If mousebutton=0 Then released=1 Else released=0 'clean clicks
    Return 0
End Function
Sub finish
    Screenunlock
    Imagedestroy frame
    End
End Sub

text mode

Screenres 320,240,32

'global variables globales
Dim Shared As Integer b(3,3) 'tablero
Dim Shared As Integer mx, my, btns, ox, oy

'prueba para ganar posición
'3 victorias horizontales
Function TestWin(t As Integer) As Integer
    Dim As Integer win = 0
    
    If b(0,0)= t And b(1,0)= t And b(2,0)= t Then win = t
    If b(0,1)= t And b(1,1)= t And b(2,1)= t Then win = t   
    If b(0,2)= t And b(1,2)= t And b(2,2)= t Then win = t
    
    '3 en vertical gana
    If b(0,0)= t And b(0,1)= t And b(0,2)= t Then win = t
    If b(1,0)= t And b(1,1)= t And b(1,2)= t Then win = t
    If b(2,0)= t And b(2,1)= t And b(2,2)= t Then win = t
    
    'cruzada gana
    If b(0,0)= t And b(1,1)= t And b(2,2)= t Then win = t
    If b(2,0)= t And b(1,1)= t And b(0,2)= t Then win = t
    
    Return win
End Function

Sub InicializarTablero()
    For j As Integer = 0 To 2
        For i As Integer = 0 To 2
            b(i,j)=0
        Next i
    Next j
End Sub

Sub DibujaTablero()
    Locate 1,1 : Print "+---+---+---+"
    For j As Integer = 0 To 2
        Print "|";
        For i As Integer = 0 To 2
            If b(i,j) = 0 Then Print "   |";
            If b(i,j) = 1 Then Print " x |";
            If b(i,j) = 2 Then Print " o |";
        Next i
        Print !"\n+---+---+---+"
    Next j
End Sub

Function MovimientoHumano() As Integer
    DibujaTablero()
    
    Print !"\n HAZ CLICK CON EL MOUSE"
    Print "EN LA CASILLA QUE ELIJAS"
    Dim As Integer opcion = -1
    
    While opcion = -1
        Getmouse mx,my,,btns
        While btns <> 1 'esperar a pulsar botón
            Getmouse mx,my,,btns
        Wend
        
        mx = (mx-4)\32
        my = (my-4)\16
        If mx >= 0 And mx < 3 And my >= 0 And my < 3 Then
            If b(mx,my) = 0 Then opcion = mx+my*3 'Casilla vacía?
        End If
        While btns=1
            Getmouse mx,my,,btns
        Wend
    Wend
    
    Return opcion
End Function

Function MovimientoAleatorio() As Integer   
    Dim As Integer opcion, i, j
    opcion = Int(Rnd(1)*9)
    j = Int(opcion/3)
    i = opcion - Int(opcion/3)*3
    
    While b(i,j) <> 0 Or (opcion > 8 Or opcion < 0)
        opcion = Int(Rnd(1)*9)
        j = Int(opcion/3)
        i = opcion - Int(opcion/3)*3       
    Wend
    
    Return j*3+i
End Function

Function MovimientoInteligente(t As Integer) As Integer
    Dim As Integer i, j, opcion, t2
    opcion = -1 'opcion aún no seleccionada
    
    'obtener la ficha t2 de los oponentes
    If t = 1 Then t2 = 2 Else t2 = 1   
    
    'prueba para la casilla central
    If b(1,1) = 0 Then opcion = 4   
    
    'prueba para ganar 
    If opcion = -1 Then
        If b(0,0)= 0 And b(1,0)= t And b(2,0)= t Then opcion = 0
        If b(0,0)= t And b(1,0)= 0 And b(2,0)= t Then opcion = 1
        If b(0,0)= t And b(1,0)= t And b(2,0)= 0 Then opcion = 2
        If b(0,1)= 0 And b(1,1)= t And b(2,1)= t Then opcion = 3
        If b(0,1)= t And b(1,1)= 0 And b(2,1)= t Then opcion = 4       
        If b(0,1)= t And b(1,1)= t And b(2,1)= 0 Then opcion = 5
        If b(0,2)= 0 And b(1,2)= t And b(2,2)= t Then opcion = 6
        If b(0,2)= t And b(1,2)= 0 And b(2,2)= t Then opcion = 7
        If b(0,2)= t And b(1,2)= t And b(2,2)= 0 Then opcion = 8      
        
        '3 bloques verticales
        If b(0,0)= 0 And b(0,1)= t And b(0,2)= t Then opcion = 0
        If b(0,0)= t And b(0,1)= 0 And b(0,2)= t Then opcion = 3
        If b(0,0)= t And b(0,1)= t And b(0,2)= 0 Then opcion = 6
        If b(1,0)= 0 And b(1,1)= t And b(1,2)= t Then opcion = 1
        If b(1,0)= t And b(1,1)= 0 And b(1,2)= t Then opcion = 4
        If b(1,0)= t And b(1,1)= t And b(1,2)= 0 Then opcion = 7
        If b(2,0)= 0 And b(2,1)= t And b(2,2)= t Then opcion = 2
        If b(2,0)= t And b(2,1)= 0 And b(2,2)= t Then opcion = 5
        If b(2,0)= t And b(2,1)= t And b(2,2)= 0 Then opcion = 8
        
        'bloques cruzados 
        If b(0,0)= 0 And b(1,1)= t And b(2,2)= t Then opcion = 0
        If b(0,0)= t And b(1,1)= 0 And b(2,2)= t Then opcion = 4
        If b(0,0)= t And b(1,1)= t And b(2,2)= 0 Then opcion = 8
        If b(2,0)= 0 And b(1,1)= t And b(0,2)= t Then opcion = 2
        If b(2,0)= t And b(1,1)= 0 And b(0,2)= t Then opcion = 4
        If b(2,0)= t And b(1,1)= t And b(0,2)= 0 Then opcion = 6
    End If
    
    'prueba para bloques
    If opcion = -1 Then
        If b(0,0)= 0 And b(1,0)= t2 And b(2,0)= t2 Then opcion = 0
        If b(0,0)= t2 And b(1,0)= 0 And b(2,0)= t2 Then opcion = 1
        If b(0,0)= t2 And b(1,0)= t2 And b(2,0)= 0 Then opcion = 2
        If b(0,1)= 0 And b(1,1)= t2 And b(2,1)= t2 Then opcion = 3
        If b(0,1)= t2 And b(1,1)= 0 And b(2,1)= t2 Then opcion = 4
        If b(0,1)= t2 And b(1,1)= t2 And b(2,1)= 0 Then opcion = 5
        If b(0,2)= 0 And b(1,2)= t2 And b(2,2)= t2 Then opcion = 6
        If b(0,2)= t2 And b(1,2)= 0 And b(2,2)= t2 Then opcion = 7
        If b(0,2)= t2 And b(1,2)= t2 And b(2,2)= 0 Then opcion = 8
        
        '3 bloques verticales
        If b(0,0)= 0 And b(0,1)= t2 And b(0,2)= t2 Then opcion = 0
        If b(0,0)= t2 And b(0,1)= 0 And b(0,2)= t2 Then opcion = 3
        If b(0,0)= t2 And b(0,1)= t2 And b(0,2)= 0 Then opcion = 6
        If b(1,0)= 0 And b(1,1)= t2 And b(1,2)= t2 Then opcion = 1
        If b(1,0)= t2 And b(1,1)= 0 And b(1,2)= t2 Then opcion = 4
        If b(1,0)= t2 And b(1,1)= t2 And b(1,2)= 0 Then opcion = 7
        If b(2,0)= 0 And b(2,1)= t2 And b(2,2)= t2 Then opcion = 2
        If b(2,0)= t2 And b(2,1)= 0 And b(2,2)= t2 Then opcion = 5
        If b(2,0)= t2 And b(2,1)= t2 And b(2,2)= 0 Then opcion = 8
        
        'bloques cruzados
        If b(0,0)= 0 And b(1,1)= t2 And b(2,2)= t2 Then opcion = 0
        If b(0,0)= t2 And b(1,1)= 0 And b(2,2)= t2 Then opcion = 4
        If b(0,0)= t2 And b(1,1)= t2 And b(2,2)= 0 Then opcion = 8
        If b(2,0)= 0 And b(1,1)= t2 And b(0,2)= t2 Then opcion = 2
        If b(2,0)= t2 And b(1,1)= 0 And b(0,2)= t2 Then opcion = 4
        If b(2,0)= t2 And b(1,1)= t2 And b(0,2)= 0 Then opcion = 6
    End If
    
    If opcion = -1 Then        
        If b(0,0) = 0 Then opcion = 0
        If b(2,0) = 0 Then opcion = 2
        If b(0,2) = 0 Then opcion = 6
        If b(2,2) = 0 Then opcion = 8
    End If
    
    'no hay opción de hacer una elección al azar 
    If opcion = -1 Then
        opcion = Int(Rnd(1)*9)
        j = Int(opcion/3)
        i = opcion - Int(opcion/3)*3
        
        'encontrar una casilla vacía
        While b(i,j) <> 0
            opcion = Int(Rnd(1)*9)
            j = Int(opcion/3)
            i = opcion - Int(opcion/3)*3
        Wend
    End If
    
    Return opcion   
End Function


InicializarTablero()
DibujaTablero()
Dim As Integer resultado
Dim As Integer jugador = 1
Dim As Integer ContarMovimientos = 0
Dim As Integer ContarPartidas = 0
Dim As Integer movimiento = 0
Dim As Integer i, j

Do   
    'alternar jugadores
    If jugador = 1 Then jugador = 2 Else jugador = 1
    
    'selecciona tipo de movimiento para cada jugador
    If jugador = 1 Then
        movimiento = MovimientoHumano()
    Else
        movimiento = MovimientoInteligente(2)
    End If
    
    'print "movimiento ="; movimiento
    'print "jugador ="; jugador
    
    'convertir la elección a las coordenadas del tablero i,j
    j = Int(movimiento/3)
    i = movimiento - (j*3)
    b(i,j) = jugador 'ingrese la ficha de jugador 1 o 2
    
    resultado = TestWin(jugador) 'comprobar si el jugador ha ganado
    
    DibujaTablero()
    ContarMovimientos += 1
    
    '=======================================================
    'Comprobar final de partida y/o un resultado de victoria
    '=======================================================
    If ContarMovimientos = 9 Or resultado <> 0 Then
        DibujaTablero()
        If resultado = 0 Then Print !"\n        EMPATE         "
        If resultado = 1 Then Print !"\n        x GANA         "
        If resultado = 2 Then Print !"\n        o GANA         "
        Print Space(28)
        Print "PULSA BARRA ESPACIADORA PARA"
        Print "OTRA PARTIDA, ESC PARA SALIR"
        Sleep
        Cls
        
        InicializarTablero() 'reiniciar tablero
        ContarMovimientos = 0
        ContarPartidas += 1
    End If
Loop Until Multikey(&H01)
End

Microsoft Small Basic

This game has a simple AI.

place1 = 1
place2 = 2
place3 = 3
place4 = 4
place5 = 5
place6 = 6
place7 = 7
place8 = 8
place9 = 9
symbol1 = "X"
symbol2 = "O"
reset:
TextWindow.Clear()
TextWindow.Write(place1 + " ")
TextWindow.Write(place2 + " ")
TextWindow.WriteLine(place3 + " ")
TextWindow.Write(place4 + " ")
TextWindow.Write(place5 + " ")
TextWindow.WriteLine(place6 + " ")
TextWindow.Write(place7 + " ")
TextWindow.Write(place8 + " ")
TextWindow.WriteLine(place9 + " ")
TextWindow.WriteLine("Where would you like to go to (choose a number from 1 to 9 and press enter)?")
n = TextWindow.Read()
If n = 1 then
  If place1 = symbol1 or place1 = symbol2 then
    Goto ai
  Else
    place1 = symbol1
  EndIf
ElseIf n = 2 then
  If place2 = symbol1 or place2 = symbol2 then
    Goto ai
  Else
    place2 = symbol1
  EndIf
ElseIf n = 3 then
  If place3 = symbol1 or place3 = symbol2 then
    Goto ai
  Else
    place3 = symbol1
  EndIf
ElseIf n = 4 then
  If place4 = symbol1 or place4 = symbol2 then
    Goto ai
  Else
    place4 = symbol1
  EndIf
ElseIf n = 5 then
  If place5 = symbol1 or place5 = symbol2 then
    Goto ai
  Else
    place5 = symbol1
  EndIf
ElseIf n = 6 then
  If place6 = symbol1 or place6 = symbol2 then
    Goto ai
  Else
    place6 = symbol1
  EndIf
ElseIf n = 7 then
  If place8 = symbol1 or place7 = symbol2 then
    Goto ai
  Else
    place7 = symbol1
  EndIf
ElseIf n = 8 then
  If place8 = symbol1 or place8 = symbol2 then
    Goto ai
  Else
    place8 = symbol1
  EndIf
ElseIf n = 9 then
  If place9 = symbol1 or place9 = symbol2 then
    Goto ai
  Else
    place9 = symbol1
  EndIf
EndIf
Goto ai
ai:
n = Math.GetRandomNumber(9)
If n = 1 then
  If place1 = symbol1 or place1 = symbol2 then
    Goto ai
  Else
    place1 = symbol2
  EndIf
ElseIf n = 2 then
  If place2 = symbol1 or place2 = symbol2 then
    Goto ai
  Else
    place2 = symbol2
  EndIf
ElseIf n = 3 then
  If place3 = symbol1 or place3 = symbol2 then
    Goto ai
  Else
    place3 = symbol2
  EndIf
ElseIf n = 4 then
  If place4 = symbol1 or place4 = symbol2 then
    Goto ai
  Else
    place4 = symbol2
  EndIf
ElseIf n = 5 then
  If place5 = symbol1 or place5 = symbol2 then
    Goto ai
  Else
    place5 = symbol2
  EndIf
ElseIf n = 6 then
  If place6 = symbol1 or place6 = symbol2 then
    Goto ai
  Else
    place6 = symbol2
  EndIf
ElseIf n = 7 then
  If place7 = symbol1 or place7 = symbol2 then
    Goto ai
  Else
    place7 = symbol2
  EndIf
ElseIf n = 8 then
  If place8 = symbol1 or place8 = symbol2 then
    Goto ai
  Else
    place8 = symbol2
  EndIf
ElseIf n = 9 then
  If place9 = symbol1 or place9 = symbol2 then
    Goto ai
  Else
    place9 = symbol2
  EndIf
EndIf
If place1 = symbol1 and place2 = symbol1 and place3 = symbol1 or place4 = symbol1 and place5 = symbol1 and place6 = symbol1 or place7 = symbol1 and place8 = symbol1 and place9 = symbol1 or place1 = symbol1 and place4 = symbol1 and place7 = symbol1 or place2 = symbol1 and place5 = symbol1 and place8 = symbol1 or place3 = symbol1 and place6 = symbol1 and place9 = symbol1 or place1 = symbol1 and place5 = symbol1 and place9 = symbol1 or place3 = symbol1 and place5 = symbol1 and place7 = symbol1 then
  TextWindow.WriteLine("Player 1 (" + symbol1 + ") wins!")
ElseIf place1 = symbol2 and place2 = symbol2 and place3 = symbol2 or place4 = symbol2 and place5 = symbol2 and place6 = symbol2 or place7 = symbol2 and place8 = symbol2 and place9 = symbol2 or place1 = symbol2 and place4 = symbol2 and place7 = symbol2 or place2 = symbol2 and place5 = symbol2 and place8 = symbol2 or place3 = symbol2 and place6 = symbol2 and place9 = symbol2 or place1 = symbol2 and place5 = symbol2 and place8 = symbol2 or place3 = symbol2 and place5 = symbol2 and place7 = symbol2 then
  TextWindow.WriteLine("Player 2 (" + symbol2 + ") wins!")
Else
  Goto reset
EndIf

QuickBASIC

Works with: QuickBasic version 4.5
' Tic-tac-toe

DECLARE FUNCTION Win% (Piece AS STRING)
DECLARE FUNCTION SpacesFilled% ()
DECLARE SUB ClearBoard ()
DECLARE SUB DisplayNumberedBoard ()
DECLARE SUB DisplayPiecedBoard ()
DECLARE FUNCTION Evaluate% (Me AS STRING, Him AS STRING)

DIM SHARED Board(8) AS STRING * 1, BestMove AS INTEGER
DIM SHARED WinPos(7, 2) AS INTEGER
DIM SHARED MyPiece AS STRING, HisPiece AS STRING

FOR I = 0 TO 7
  FOR J = 0 TO 2
    READ WinPos(I, J)
  NEXT J
NEXT I
' Winning positions
DATA 0, 1, 2, 3, 4, 5, 6, 7, 8, 0, 3, 6, 1, 4, 7, 2, 5, 8, 0, 4, 8, 2, 4, 6
MyWinsCnt = 0: HisWinsCnt = 0: DrawsCnt = 0
CompFirst = -1 '  It be reversed, so human goes first
CLS
PRINT
PRINT "            TIC-TAC-TOE"
PRINT
PRINT "In this version, X always goes first."
PRINT "The board is numbered:"
DO
  CompFirst = NOT CompFirst ' reverse who goes first
  MovesCnt = 0
  PRINT
  DisplayNumberedBoard
  PRINT
  IF CompFirst THEN PRINT "I go first." ELSE PRINT "You go first. ";
  ClearBoard
  IF CompFirst THEN MyPiece = "X": HisPiece = "O" ELSE MyPiece = "O": HisPiece = "X"
  ' -1: human; 1: computer; 0: nobody
  IF CompFirst THEN Mover = 1 ELSE Mover = -1
  WHILE Mover <> 0
    SELECT CASE Mover
      CASE 1
        IF MovesCnt = 0 THEN
          BestMove = INT(RND * 9)
        ELSEIF MovesCnt = 1 THEN
          IF Board(4) <> " " THEN BestMove = INT(RND * 2) * 6 + INT(RND * 2) * 2 ELSE BestMove = 4
        ELSE
          T = Evaluate(MyPiece, HisPiece)
        END IF
        Board(BestMove) = MyPiece
        MovesCnt = MovesCnt + 1
        PRINT
        CALL DisplayPiecedBoard
        PRINT
        IF Win(MyPiece) THEN
          MyWinsCnt = MyWinsCnt + 1
          PRINT "I win!"
          Mover = 0
        ELSEIF SpacesFilled THEN
          DrawsCnt = DrawsCnt + 1
          PRINT "It's a draw. Thank you."
          Mover = 0
        ELSE
          Mover = -1
        END IF
      CASE -1
        DO
          INPUT "Where do you move? ", I
          IF I < 1 OR I > 9 THEN
            PRINT "Illegal! ";
          ELSEIF Board(I - 1) <> " " THEN
            PRINT "Place already occupied. ";
          ELSE
            EXIT DO
          END IF
        LOOP
        Board(I - 1) = HisPiece
        MovesCnt = MovesCnt + 1
        PRINT
        CALL DisplayPiecedBoard
        PRINT
        IF Win(HisPiece) THEN
          HisWinsCnt = HisWinsCnt + 1
          PRINT "You beat me! Good game."
          Mover = 0
        ELSEIF SpacesFilled THEN
          DrawsCnt = DrawsCnt + 1
          PRINT "It's a draw. Thank you."
          Mover = 0
        ELSE
          Mover = 1
        END IF
    END SELECT
  WEND
  PRINT
  INPUT "Another game (y/n)? ", Answ$
LOOP UNTIL UCASE$(Answ$) <> "Y"
PRINT
PRINT "Final score:"
PRINT "You won", HisWinsCnt; "game";
IF HisWinsCnt <> 1 THEN PRINT "s";
PRINT "."
PRINT "I won", MyWinsCnt; "game";
IF MyWinsCnt <> 1 THEN PRINT "s";
PRINT "."
PRINT "We tied", DrawsCnt; "game";
IF DrawsCnt <> 1 THEN PRINT "s";
PRINT "."
PRINT "See you later!"
END

SUB ClearBoard
  FOR I = 0 TO 8: Board(I) = " ": NEXT I
END SUB

SUB DisplayNumberedBoard
  FOR I = 0 TO 8 STEP 3
    PRINT I + 1; "|"; I + 2; "|"; I + 3
    IF I <> 6 THEN PRINT "---+---+---"
  NEXT I
END SUB

SUB DisplayPiecedBoard
  FOR I = 0 TO 8 STEP 3
    PRINT " "; Board(I); " | "; Board(I + 1); " | "; Board(I + 2)
    IF I <> 6 THEN PRINT "---+---+---"
  NEXT I
END SUB

FUNCTION Evaluate% (Me AS STRING, Him AS STRING)
  ' Recursive algorithm
  IF Win(Me) THEN Evaluate = 1: EXIT FUNCTION
  IF Win(Him) THEN Evaluate = -1: EXIT FUNCTION
  IF SpacesFilled THEN Evaluate = 0: EXIT FUNCTION
  LoseFlag = 1
  FOR I = 0 TO 8
    IF Board(I) = " " THEN
      Board(I) = Me ' Try the move.
      V = Evaluate(Him, Me)
      Board(I) = " " ' Restore the empty space.
      IF V = -1 THEN BestMove = I: Evaluate = 1: EXIT FUNCTION
      IF V = 0 THEN LoseFlag = 0: SafeMove = I
    END IF
  NEXT
  BestMove = SafeMove
  Evaluate = -LoseFlag
END FUNCTION

FUNCTION SpacesFilled%
  FOR I = 0 TO 8
    IF Board(I) = " " THEN SpacesFilled = 0: EXIT FUNCTION
  NEXT I
  SpacesFilled = -1
END FUNCTION

FUNCTION Win% (Piece AS STRING)
  FOR I = 0 TO 7
    IF Board(WinPos(I, 0)) = Piece AND Board(WinPos(I, 1)) = Piece AND Board(WinPos(I, 2)) = Piece THEN Win = -1: EXIT FUNCTION
  NEXT I
  Win = 0
END FUNCTION

RapidQ

Translation of: QuickBASIC
' Tic-tac-toe
' Console application

DECLARE FUNCTION Win (Piece AS STRING) AS INTEGER
DECLARE FUNCTION SpacesFilled () AS INTEGER
DECLARE SUB ClearBoard ()
DECLARE SUB DisplayNumberedBoard ()
DECLARE SUB DisplayPiecedBoard ()
DECLARE FUNCTION Evaluate (Me AS STRING, Him AS STRING) AS INTEGER

DIM Board(8) AS STRING * 1, BestMove AS INTEGER
DIM WinPos(7, 2) AS INTEGER
DIM MyPiece AS STRING, HisPiece AS STRING

FOR I = 0 TO 7
  FOR J = 0 TO 2
    READ WinPos(I, J)
  NEXT J
NEXT I
' Winning positions
DATA 0, 1, 2, 3, 4, 5, 6, 7, 8, 0, 3, 6, 1, 4, 7, 2, 5, 8, 0, 4, 8, 2, 4, 6
MyWinsCnt = 0: HisWinsCnt = 0: DrawsCnt = 0
CompFirst = -1 ' It be reversed, so human goes first
CLS
PRINT
PRINT "            TIC-TAC-TOE"
PRINT
PRINT "In this version, X always goes first."
PRINT "The board is numbered:"
DO
  CompFirst = NOT CompFirst ' reverse who goes first
  MovesCnt = 0
  PRINT
  DisplayNumberedBoard
  PRINT
  PRINT IIF(CompFirst, "I go first.", "You go first.")
  ClearBoard
  IF CompFirst THEN MyPiece = "X": HisPiece = "O" ELSE MyPiece = "O": HisPiece = "X"
  ' -1: human; 1: computer; 0: nobody
  Mover = IIF(CompFirst, 1, -1)
  WHILE Mover <> 0
    SELECT CASE Mover
      CASE 1
        IF MovesCnt = 0 THEN
          BestMove = INT(RND * 9)
        ELSEIF MovesCnt = 1 THEN
          BestMove = IIF(Board(4) <> " ", INT(RND * 2) * 6 + INT(RND * 2) * 2, 4)
        ELSE
          T = Evaluate(MyPiece, HisPiece)
        END IF
        Board(BestMove) = MyPiece
        INC(MovesCnt)
        PRINT
        CALL DisplayPiecedBoard
        PRINT
        IF Win(MyPiece) THEN
          INC(MyWinsCnt)
          PRINT "I win!"
          Mover = 0
        ELSEIF SpacesFilled THEN
          INC(DrawsCnt)
          PRINT "It's a draw. Thank you."
          Mover = 0
        ELSE
          Mover = -1
        END IF
      CASE -1
        DO
          INPUT "Where do you move? ",I
          IF I < 1 OR I > 9 THEN
            PRINT "Illegal! ";
          ELSEIF Board(I - 1) <> " " THEN
            PRINT "Place already occupied. ";
          ELSE
            EXIT DO
          END IF
        LOOP
        Board(I - 1) = HisPiece
        INC(MovesCnt)
        PRINT
        CALL DisplayPiecedBoard
        PRINT
        IF Win(HisPiece) THEN
          INC(HisWinsCnt)
          PRINT "You beat me! Good game."
          Mover = 0
        ELSEIF SpacesFilled THEN
          INC(DrawsCnt)
          PRINT "It's a draw. Thank you."
          Mover = 0
        ELSE
          Mover = 1
        END IF
    END SELECT
  WEND
  PRINT
  INPUT "Another game (y/n)? ", Answ$
LOOP UNTIL UCASE$(Answ$) <> "Y"
PRINT
PRINT "Final score:"
PRINT "You won "; HisWinsCnt; " game"; IIF(HisWinsCnt <> 1, "s.", ".")
PRINT "I won "; MyWinsCnt; " game"; IIF(MyWinsCnt <> 1, "s.", ".")
PRINT "We tied "; DrawsCnt; " game"; IIF(DrawsCnt <> 1, "s.", ".")
PRINT "See you later!"
END

SUB ClearBoard
  FOR I = 0 TO 8: Board(I) = " ": NEXT I
END SUB

SUB DisplayNumberedBoard
  FOR I = 0 TO 8 STEP 3
    PRINT " "; I + 1; " | "; I + 2; " | "; I + 3
    IF I <> 6 THEN PRINT "---+---+---"
  NEXT I
END SUB

SUB DisplayPiecedBoard
  FOR I = 0 TO 8 STEP 3
    PRINT " "; Board(I); " | "; Board(I + 1); " | "; Board(I + 2)
    IF I <> 6 THEN PRINT "---+---+---"
  NEXT I
END SUB

FUNCTION Evaluate (Me AS STRING, Him AS STRING)
  ' Recursive algorithm
  DIM I AS INTEGER, SafeMove AS INTEGER, V AS INTEGER, LoseFlag AS INTEGER
  IF Win(Me) THEN Evaluate = 1: EXIT FUNCTION
  IF Win(Him) THEN Evaluate = -1: EXIT FUNCTION
  IF SpacesFilled THEN Evaluate = 0: EXIT FUNCTION
  LoseFlag = 1
  I = 0
  WHILE I <= 8
    IF Board(I) = " " THEN
      Board(I) = Me ' Try the move.
      V = Evaluate(Him, Me)
      Board(I) = " " ' Restore the empty space.
      IF V = -1 THEN BestMove = I: Evaluate = 1: EXIT FUNCTION
      IF V = 0 THEN LoseFlag = 0: SafeMove = I
    END IF
    INC(I)
  WEND
  BestMove = SafeMove
  Evaluate = -LoseFlag
END FUNCTION

FUNCTION SpacesFilled
  FOR I = 0 TO 8
    IF Board(I) = " " THEN SpacesFilled = 0: EXIT FUNCTION
  NEXT I
  SpacesFilled = -1
END FUNCTION

FUNCTION Win (Piece AS STRING)
  FOR I = 0 TO 7
    IF Board(WinPos(I, 0)) = Piece AND Board(WinPos(I, 1)) = Piece AND Board(WinPos(I, 2)) = Piece THEN Win = -1: EXIT FUNCTION
  NEXT I
  Win = 0
END FUNCTION

Run BASIC

' ---------------------------
'  TIC TAC TOE
' ---------------------------
winBox$ = "123 456 789 159 147 258 369 357"
boxPos$ = "123 231 456 564 789 897 159 591 357 753 132 465 798 174 285 396 159 471 582 693 147 258 369 195 375"
ai$     = "519628374"
ox$     = "OX" 
[newGame]
for i = 1 to 9
 box$(i) = ""
next i
goto [shoTic]

[loop]
for j = 1 to 2
 tic$ = mid$(ox$,j,1)
 for i = 1 to 25
  b$	= word$(boxPos$,i," ")
  b1	= val(mid$(b$,1,1))
  b2	= val(mid$(b$,2,1))
  b3	= val(mid$(b$,3,1))
  if box$(b1) = tic$ AND box$(b2) = tic$ AND box$(b3) = "" then
     box$(b3)  = "O"
     goto [shoTic]
 end if
 next i
next j
if box$(1) = "O" AND box$(5) = "X" and box$(9) = "X" then
 if box$(3) = "" then
   box$(3) = "O"
   goto [shoTic]
 end if
 if box$(7) = "" then
   box$(7) = "O"
   goto [shoTic]
 end if
end if
for i = 1 to 9
 b1 = val(mid$(ai$,i,1))
 if box$(b1) = "" then
   box$(b1)  = "O"
   exit for
 end if
next i

[shoTic]
cls
' ----------------------------------------
' show tic tac toe screen
' ----------------------------------------
html "<table border=1 width=300px height=225px><TR>"
for i = 1 to 9
  html "<td align=center width=33%><h1>"
    if box$(i) <> "" then 
     html box$(i)
    else
    button #box, " ";box$(i);" ", [doTic]
           #box  setkey(str$(i))
    end if
    if i mod 3 = 0 then html "</tr><tr>"
next i
html "</table>"
gosub [checkWin]
wait

[doTic]
box$(val(EventKey$)) = "X"
turn          = 1
gosub [checkWin]
goto [loop]

' --- check for a winner ----------
[checkWin]
for i = 1 to 8
 b$ = word$(winBox$,i," ")
 b1 = val(mid$(b$,1,1))
 b2 = val(mid$(b$,2,1))
 b3 = val(mid$(b$,3,1))
 if box$(b1) = "O" and box$(b2) = "O" and box$(b3) = "O" then
   print "You Lose!"
   goto [playAgain]
 end if
 if box$(b1) = "X" and box$(b2) = "X" and box$(b3) = "X" then
   print "You Win!"
   goto [playAgain]
 end if
next i

moveCount = 0
for i = 1 to 9
 if box$(i) <> "" then moveCount = moveCount + 1 
next i
if moveCount = 9 then
  print "Draw!"
  goto [playAgain]
end if
RETURN

[playAgain]
input "Play again (y/n)";p$
if upper$(p$) = "Y" then goto [newGame]
end

Tiny BASIC

    REM Tic-tac-toe for Tiny BASIC
    REM
    REM Released as public domain by Damian Gareth Walker, 2019
    REM Created: 21-Sep-2019
    
    REM --- Variables
    REM     A   - first square in line examined
    REM     B   - second square in line examined
    REM     C   - third square in line examined
    REM     D   - player whose pieces to count
    REM     E   - number of DREM s pieces on a line
    REM     F   - first square of line to examine
    REM     G   - game winner
    REM     H   - which side the human takes
    REM     I   - increment for line to examine
    REM     L   - line to examine
    REM     M   - where to move (various uses)
    REM     N   - piece found in a square
    REM     P   - player currently playing
    REM     Q   - square to examine
    REM     R-Z - contents of the board

    REM --- Main Program
    GOSUB 40
    GOSUB 60
    GOSUB 80
    END

    REM --- Subroutine to initialise the game
    REM     Outputs: H - Human play order
    REM              P - Whose turn it is
 40 PRINT "Tic tac toe. Board positions are:"
    PRINT " 1  2  3"
    PRINT " 4  5  6"
    PRINT " 7  8  9"
    PRINT "Play first or second (1/2)?"
    INPUT H
    IF H<1 THEN GOTO 40
    IF H>2 THEN GOTO 40
    LET P=1
    RETURN

    REM --- Subroutine to take turns
    REM     Inputs:  H - who is the human
    REM              P - whose turn it is
    REM     Outputs: G - who won the game
 60 IF P=H THEN GOSUB 100
    IF P<>H THEN GOSUB 120
    GOSUB 200
    IF G>0 THEN RETURN
    LET P=3-P
    IF R=0 THEN GOTO 60
    IF S=0 THEN GOTO 60
    IF T=0 THEN GOTO 60
    IF U=0 THEN GOTO 60
    IF V=0 THEN GOTO 60
    IF W=0 THEN GOTO 60
    IF X=0 THEN GOTO 60
    IF Y=0 THEN GOTO 60
    IF Z=0 THEN GOTO 60
    RETURN

    REM --- Victory
    REM Inputs: H   - which side was the human
    REM         P   - player who won
 80 IF G=H THEN PRINT "You win!"
    IF G<>0 THEN IF G<>H THEN PRINT "Computer wins"
    IF G=0 THEN PRINT "A draw"
    RETURN

    REM --- Subroutine to allow the player to move
    REM     Inputs:  P   - player number
    REM     Outputs: M   - where the player wishes to move
100 PRINT "Move? "
    INPUT Q
    IF Q<1 THEN GOTO 100
    IF Q>9 THEN GOTO 100
    GOSUB 220
    IF N<>0 THEN GOTO 100
    LET M=Q
    GOSUB 240
    RETURN

    REM --- Subroutine to make the computerREM s move
    REM     Inputs:  P   - player number
    REM     Outputs: M   - the move chosen
120 LET M=0
    LET D=3-H
    GOSUB 145
    IF M>0 THEN GOTO 135
    LET D=H
    GOSUB 145
    IF M=0 THEN IF V=0 THEN LET M=5
    IF M=0 THEN IF R=0 THEN LET M=1    
    IF M=0 THEN IF T=0 THEN LET M=3    
    IF M=0 THEN IF X=0 THEN LET M=7    
    IF M=0 THEN IF Z=0 THEN LET M=9
    IF M=0 THEN IF S=0 THEN LET M=2    
    IF M=0 THEN IF U=0 THEN LET M=4    
    IF M=0 THEN IF Y=0 THEN LET M=8    
    IF M=0 THEN IF W=0 THEN LET M=6    
135 GOSUB 240
    PRINT "Computer move ",M
    RETURN

    REM --- Identify moves to win or avoid a loss
    REM     Inputs:  D   - player whose pieces weREM re counting
    REM     Changes: E   - number of pieces on line being scanned
    REM              F   - first square in winning line
    REM              I   - increment of winning line
    REM              L   - line being scanned (counter)
145 LET L=1
146 GOSUB 170
    IF E<2 THEN GOTO 152
    IF A=0 THEN LET M=F
    IF B=0 THEN LET M=F+I
    IF C=0 THEN LET M=F+I+I
    IF M>0 THEN RETURN
152 LET L=L+1
    IF L<9 THEN GOTO 146
    RETURN

    REM --- Count a playerREM s pieces on a line
    REM     Inputs:  D   - player whose pieces weREM re counting
    REM              L   - line number
    REM     Changes: F   - first square on the line
    REM              I   - increment of the line
    REM              Q   - individual squares to examine
    REM     Outputs: A   - contents of first square
    REM              B   - contents of second square
    REM              C   - contents of third square
    REM              E   - number of the playerREM s pieces
170 IF L>3 THEN GOTO 174
    LET F=3*L-2
    LET I=1
    GOTO 180
174 IF L>6 THEN GOTO 178
    LET F=L-3
    LET I=3
    GOTO 180
178 LET F=1+2*(L-7)
    LET I=4-2*(L-7)
180 LET E=0
    LET Q=F
    GOSUB 220
    LET A=N
    IF N=D THEN LET E=E+1
    LET Q=Q+I
    GOSUB 220
    LET B=N
    IF N=D THEN LET E=E+1
    LET Q=Q+I
    GOSUB 220
    LET C=N
    IF N=D THEN LET E=E+1
    RETURN

    REM --- Subroutine to check for a win
    REM     Inputs:  R-Z - board squares
    REM     Outputs: G   - the winning player (0 for neither)
200 LET G=0
    IF R>0 THEN IF R=S THEN IF S=T THEN LET G=R
    IF U>0 THEN IF U=V THEN IF V=W THEN LET G=U
    IF X>0 THEN IF X=Y THEN IF Y=Z THEN LET G=X
    IF R>0 THEN IF R=U THEN IF U=X THEN LET G=R
    IF S>0 THEN IF S=V THEN IF V=Y THEN LET G=S
    IF T>0 THEN IF T=W THEN IF W=Z THEN LET G=T
    IF R>0 THEN IF R=V THEN IF V=Z THEN LET G=R
    IF T>0 THEN IF T=V THEN IF V=X THEN LET G=T
    RETURN

    REM --- Subroutine to see what piece is in a square
    REM     Inputs:  Q   - the square to check
    REM              R-Z - the contents of the squares
    REM     Outputs: N   - the piece in that square
220 LET N=0
    IF Q=1 THEN LET N=R
    IF Q=2 THEN LET N=S
    IF Q=3 THEN LET N=T
    IF Q=4 THEN LET N=U
    IF Q=5 THEN LET N=V
    IF Q=6 THEN LET N=W
    IF Q=7 THEN LET N=X
    IF Q=8 THEN LET N=Y
    IF Q=9 THEN LET N=Z
    RETURN

    REM --- Subroutine to put a piece in a square
    REM     Inputs:  P   - the player whose piece should be placed
    REM              M   - the square to put the piece in
    REM     Changes: R-Z - the contents of the squares
240 IF M=1 THEN LET R=P
    IF M=2 THEN LET S=P
    IF M=3 THEN LET T=P
    IF M=4 THEN LET U=P
    IF M=5 THEN LET V=P
    IF M=6 THEN LET W=P
    IF M=7 THEN LET X=P
    IF M=8 THEN LET Y=P
    IF M=9 THEN LET Z=P
    RETURN

VBA

Human play first with the "X". You must choose the row and the column you want to play...

Option Explicit

Private Lines(1 To 3, 1 To 3) As String
Private Nb As Byte, player As Byte
Private GameWin As Boolean, GameOver As Boolean

Sub Main_TicTacToe()
Dim p As String

    InitLines
    printLines Nb
    Do
        p = WhoPlay
        Debug.Print p & " play"
        If p = "Human" Then
            Call HumanPlay
            GameWin = IsWinner("X")
        Else
            Call ComputerPlay
            GameWin = IsWinner("O")
        End If
        If Not GameWin Then GameOver = IsEnd
    Loop Until GameWin Or GameOver
    If Not GameOver Then
        Debug.Print p & " Win !"
    Else
        Debug.Print "Game Over!"
    End If
End Sub

Sub InitLines(Optional S As String)
Dim i As Byte, j As Byte
    Nb = 0: player = 0
    For i = LBound(Lines, 1) To UBound(Lines, 1)
        For j = LBound(Lines, 2) To UBound(Lines, 2)
            Lines(i, j) = "#"
        Next j
    Next i
End Sub

Sub printLines(Nb As Byte)
Dim i As Byte, j As Byte, strT As String
    Debug.Print "Loop " & Nb
    For i = LBound(Lines, 1) To UBound(Lines, 1)
        For j = LBound(Lines, 2) To UBound(Lines, 2)
            strT = strT & Lines(i, j)
        Next j
        Debug.Print strT
        strT = vbNullString
    Next i
End Sub

Function WhoPlay(Optional S As String) As String
    If player = 0 Then
        player = 1
        WhoPlay = "Human"
    Else
        player = 0
        WhoPlay = "Computer"
    End If
End Function

Sub HumanPlay(Optional S As String)
Dim L As Byte, C As Byte, GoodPlay As Boolean

    Do
        L = Application.InputBox("Choose the row", "Numeric only", Type:=1)
        If L > 0 And L < 4 Then
            C = Application.InputBox("Choose the column", "Numeric only", Type:=1)
            If C > 0 And C < 4 Then
                If Lines(L, C) = "#" And Not Lines(L, C) = "X" And Not Lines(L, C) = "O" Then
                    Lines(L, C) = "X"
                    Nb = Nb + 1
                    printLines Nb
                    GoodPlay = True
                End If
            End If
        End If
    Loop Until GoodPlay
End Sub

Sub ComputerPlay(Optional S As String)
Dim L As Byte, C As Byte, GoodPlay As Boolean

    Randomize Timer
    Do
        L = Int((Rnd * 3) + 1)
        C = Int((Rnd * 3) + 1)
        If Lines(L, C) = "#" And Not Lines(L, C) = "X" And Not Lines(L, C) = "O" Then
            Lines(L, C) = "O"
            Nb = Nb + 1
            printLines Nb
            GoodPlay = True
        End If
    Loop Until GoodPlay
End Sub

Function IsWinner(S As String) As Boolean
Dim i As Byte, j As Byte, Ch As String, strTL As String, strTC As String

    Ch = String(UBound(Lines, 1), S)
    'check lines & columns
    For i = LBound(Lines, 1) To UBound(Lines, 1)
        For j = LBound(Lines, 2) To UBound(Lines, 2)
            strTL = strTL & Lines(i, j)
            strTC = strTC & Lines(j, i)
        Next j
        If strTL = Ch Or strTC = Ch Then IsWinner = True: Exit For
        strTL = vbNullString: strTC = vbNullString
    Next i
    'check diagonales
    strTL = Lines(1, 1) & Lines(2, 2) & Lines(3, 3)
    strTC = Lines(1, 3) & Lines(2, 2) & Lines(3, 1)
    If strTL = Ch Or strTC = Ch Then IsWinner = True
End Function

Function IsEnd() As Boolean
Dim i As Byte, j As Byte

    For i = LBound(Lines, 1) To UBound(Lines, 1)
        For j = LBound(Lines, 2) To UBound(Lines, 2)
            If Lines(i, j) = "#" Then Exit Function
        Next j
    Next i
    IsEnd = True
End Function
Output:
Loop 0
###
###
###
Human Play
Loop 1
X##
###
###
Computer Play
Loop 2
X#O
###
###
Human Play
Loop 3
X#O
#X#
###
Computer Play
Loop 4
XOO
#X#
###
Human Play
Loop 5
XOO
#X#
##X
Human Win !

Yabasic

In the classic style.

5 REM Adaptation to Yabasic of the program published in Tim Hartnell's book "Artificial Intelligence: Concepts and Programs", with some minor modifications. 6/2018.
10 REM TICTAC
15 INPUT "English (0), Spanish (other key): " IDIOMA : IF NOT IDIOMA THEN RESTORE 2020 ELSE RESTORE 2010 END IF
20 GOSUB 1180: REM INICIALIZACION
30 REM *** REQUISITOS PREVIOS AL JUEGO ***
40 FOR J = 1 TO 9
50 A(J) = 32
60 NEXT J
70 FOR J = 1 TO 5
80 D(J) = 0
90 NEXT J
100 CCONTADOR = 0
110 R$ = ""
120 GOSUB 1070: REM IMPRESION DEL TABLERO
130 REM ** CICLO PRINCIPAL **
140 GOSUB 540: REM MOVIMIENTO DEL ORDENADOR
150 GOSUB 1070: REM IMPRESION DEL TABLERO
160 GOSUB 870: REM COMPRUEBA LA VICTORIA
170 IF R$ <> ""  GOTO 240
180 GOSUB 980: REM SE ACEPTA EL MOVIMIENTO DE LA PERSONA
190 GOSUB 1070: REM IMPRESION DEL TABLERO
200 GOSUB 870: REM COMPRUEBA LA VICTORIA
210 IF R$ = ""  GOTO 140
220 REM ** FIN DEL CICLO PRINCIPAL **
230 REM *****************************
240 REM FIN DEL JUEGO
250 GOSUB 1070: REM IMPRESION DEL TABLERO
260 PRINT: PRINT
270 IF R$ = "G"  PRINT MENSAJE$(1): BANDERA = -1
280 IF R$ = "P"  PRINT MENSAJE$(2): BANDERA = 1
290 IF R$ = "D"  PRINT MENSAJE$(3): GOTO 430
300 REM ACTUALIZACION DE LA BASE DE DATOS
310 FOR B = 1 TO 5
320 FOR J = 2 TO 9
330 IF M(J) = D(B) GOSUB 370
340 NEXT J
350 NEXT B
360 GOTO 430
370 REM ** REORDENACION DE LOS ELEMENTOS DE LA MATRIZ M **
380 TEMP = M(J + BANDERA)
390 M(J + BANDERA) = M(J)
400 M(J) = TEMP
410 J = 9
420 RETURN
430 PRINT: PRINT
440 PRINT MENSAJE$(4)
450 PRINT: PRINT
460 FOR J = 1 TO 9
470 PRINT M(J), " ";
480 NEXT J
490 PRINT: PRINT
500 PRINT MENSAJE$(5)
510 INPUT A$
520 GOTO 30
530 REM ************************
540 REM MOVIMIENTO DEL ORDENADOR
550 P = ASC("O") 
560 X = 0
570 J = 1
580 IF A(W(J)) = A(W(J + 1)) AND A(W(J + 2)) = 32 AND A(W(J)) = P  X = W(J + 2): GOTO 750
590 IF A(W(J)) = A(W(J + 2)) AND A(W(J + 1)) = 32 AND A(W(J)) = P  X = W(J + 1): GOTO 750
600 IF A(W(J + 1)) = A(W(J + 2)) AND A(W(J)) = 32 AND A(W(J + 1)) = P  X = W(J): GOTO 750
610 IF J < 21  J = J + 3: GOTO 580
620 IF P = ASC("O")  P = ASC("X"): GOTO 570
630 REM ** SI NO SE GANA SE BUSCA UN MOVIMIENTO DE BLOQUEO **
640 REM * ENTONCES SE USA LA SIGUIENTE SECCION *
650 J = 1
660 IF A(M(J)) = 32  X = M(J): GOTO 750
670 IF J < 10  J = J + 1: GOTO 660
680 H = 0
690 H = H + 1
700 X = INT(RAN(1) * 9): IF A(X) = 32  GOTO 750
710 IF H < 100  GOTO 690
720 R$ = "D": REM ES SIMPLEMENTE UN DIBUJO
730 RETURN
740 REM *********************
750 REM REALIZA EL MOVIMIENTO
760 A(X) = ASC("O")
770 CCONTADOR = CCONTADOR + 1
780 D(CCONTADOR) = X
790 BANDERA = 0
800 FOR J = 1 TO 9
810 IF A(J) = 32  BANDERA = 1
820 NEXT J
830 IF BANDERA = 0 AND R$ = ""  R$ = "D"
840 REM SI TODAS LAS CASILLAS ESTAN LLENAS Y R$ ESTA VACIO, ENTONCES ES SIMPLEMENTE UN DIBUJO
850 RETURN
860 REM *********************
870 REM COMPRUEBA LA VICTORIA
880 J = 1
890 IF A(W(J)) = 32  J = J + 3
900 IF J > 23  RETURN
910 IF A(W(J)) = A(W(J + 1)) AND A(W(J)) = A(W(J + 2))  GOTO 940
920 IF J < 22  J = J + 3: GOTO 890
930 RETURN
940 IF A(W(J)) = ASC("O")  R$ = "G": REM EL ORDENADOR GANA
950 IF A(W(J)) = ASC("X")  R$ = "P": REM EL ORDENADOR PIERDE
960 RETURN
970 REM ************************
980 REM MOVIMIENTO DE LA PERSONA
990 PRINT: PRINT
1000 PRINT MENSAJE$(6)
1010 PRINT MENSAJE$(7); : INPUT MOVIMIENTO
1020 IF MOVIMIENTO < 1 OR MOVIMIENTO > 9  GOTO 1010
1030 IF A(MOVIMIENTO) <> 32  GOTO 1010
1040 A(MOVIMIENTO) = ASC("X")
1050 RETURN
1060 REM *********************
1070 REM IMPRESION DEL TABLERO
1080 CLEAR SCREEN
1090 PRINT: PRINT: PRINT
1100 PRINT " 1 : 2 : 3        ", CHR$(A(1)), " : ", CHR$(A(2)), " : ", CHR$(A(3))
1110 PRINT "-----------      ------------"
1120 PRINT " 4 : 5 : 6        ", CHR$(A(4)), " : ", CHR$(A(5)), " : ", CHR$(A(6))
1130 PRINT "-----------      ------------"
1140 PRINT " 7 : 8 : 9        ", CHR$(A(7)), " : ", CHR$(A(8)), " : ", CHR$(A(9))
1150 PRINT
1160 RETURN
1170 REM **************
1180 REM INICIALIZACION
1190 CLEAR SCREEN
1200 DIM A(9) : REM TABLERO
1210 DIM M(10) : REM ACCESO A LA BASE DE DATOS
1220 DIM W(24) : REM DATOS DE VICTORIA O BLOQUEO
1230 DIM D(5) : REM ACCESO AL MOVIMIENTO EN EL JUEGO ACTUAL
1235 DIM MENSAJE$(1) : READ M$ : N = TOKEN(M$,MENSAJE$(),",") : RESTORE
1240 REM DATOS DE VICTORIA O BLOQUEO
1250 FOR J = 1 TO 24
1260 READ W(J)
1270 NEXT J
1280 DATA 1, 2, 3, 4, 5, 6, 7, 8, 9
1290 DATA 1, 4, 7, 2, 5, 8, 3, 6, 9
1300 DATA 1, 5, 9, 3, 5, 7
1310 REM BASE INICIAL DE DATOS
1320 FOR J = 1 TO 10
1330 READ M(J)
1340 NEXT J
1350 DATA 2, 6, 8, 4, 7, 3, 1, 9, 5, 2
1360 RETURN
2000 REM MENSAJES EN ESPAÑOL
2010 DATA "YO GANO,TU GANAS,ES SIMPLEMENTE UN DIBUJO,ESTA ES MI PRIORIDAD ACTUALIZADA,PULSE LA TECLA <RETURN> PARA CONTINUAR,REALICE SU MOVIMIENTO,MOVIMIENTO: "
2020 DATA "I WIN,YOU WIN,IT'S JUST A DRAWING,THIS IS MY PRIORITY UPDATE,PRESS <RETURN> TO CONTINUE,TO MAKE YOUR MOVE,MOVEMENT: "

Batch File

This is just a game between two human players.

@echo off
setlocal enabledelayedexpansion
:newgame
set a1=1
set a2=2
set a3=3
set a4=4
set a5=5
set a6=6
set a7=7
set a8=8
set a9=9
set ll=X
set /a zz=0
:display1
cls
echo Player: %ll%
echo %a7%_%a8%_%a9%
echo %a4%_%a5%_%a6%
echo %a1%_%a2%_%a3%
set /p myt=Where would you like to go (choose a number from 1-9 and press enter)?
if !a%myt%! equ %myt% (
set a%myt%=%ll%
goto check
)
goto display1
:check
set /a zz=%zz%+1
if %zz% geq 9 goto newgame
if %a7%+%a8%+%a9% equ %ll%+%ll%+%ll% goto win
if %a4%+%a5%+%a6% equ %ll%+%ll%+%ll% goto win
if %a1%+%a2%+%a3% equ %ll%+%ll%+%ll% goto win
if %a7%+%a5%+%a3% equ %ll%+%ll%+%ll% goto win
if %a1%+%a5%+%a9% equ %ll%+%ll%+%ll% goto win
if %a7%+%a4%+%a1% equ %ll%+%ll%+%ll% goto win
if %a8%+%a5%+%a2% equ %ll%+%ll%+%ll% goto win
if %a9%+%a6%+%a3% equ %ll%+%ll%+%ll% goto win
goto %ll%
:X
set ll=O
goto display1
:O
set ll=X
goto display1
:win
echo %ll% wins!
pause 
goto newgame

Advanced

This code makes a version of Tic Tac Toe with more features:

@ECHO OFF
:BEGIN  
  REM Skill level
  set sl=
  cls
  echo                       Tic Tac Toe                                 (Q to quit)
  echo.
  echo.
  echo        Pick your skill level (press a number)
  echo.
  echo               (1) Children under 6
  echo               (2) Average Mental Case
  echo               (3) Oversized Ego  
  CHOICE /c:123q /n > nul
  if errorlevel 4 goto end
  if errorlevel 3 set sl=3
  if errorlevel 3 goto layout
  if errorlevel 2 set sl=2
  if errorlevel 2 goto layout
  set sl=1

:LAYOUT
  REM Player turn ("x" or "o")
  set pt=
  REM Game winner ("x" or "o")
  set gw=
  REM No moves
  set nm=
  REM Set to one blank space after equal sign (check with cursor end)
  set t1= 
  set t2= 
  set t3= 
  set t4= 
  set t5= 
  set t6= 
  set t7= 
  set t8= 
  set t9= 

:UPDATE
  cls
  echo   (S to set skill level)       Tic Tac Toe                         (Q to quit)
  echo.
  echo                               You are the X player. 
  echo                    Press the number where you want to put an X.     
  echo.
  echo   Skill level %sl%                    7 8 9 
  echo                                       4 5 6
  echo                                       1 2 3
  echo.
  echo                                       :   :
  echo                                     %t1% : %t2% : %t3%
  echo                                   ....:...:....
  echo                                     %t4% : %t5% : %t6%
  echo                                   ....:...:....
  echo                                     %t7% : %t8% : %t9%
  echo                                       :   :
  if "%gw%"=="x" goto winx2
  if "%gw%"=="o" goto wino2
  if "%nm%"=="0" goto nomoves

:PLAYER
  set pt=x
  REM Layout is for keypad. Change CHOICE to "/c:123456789sq  /n > nul"
  REM for numbers to start at top left (also change user layout above).
  CHOICE /c:789456123sq /n > nul
  if errorlevel 11 goto end
  if errorlevel 10 goto begin
  if errorlevel 9 goto 9
  if errorlevel 8 goto 8
  if errorlevel 7 goto 7
  if errorlevel 6 goto 6
  if errorlevel 5 goto 5
  if errorlevel 4 goto 4
  if errorlevel 3 goto 3
  if errorlevel 2 goto 2
  goto 1

:1  
  REM Check if "x" or "o" already in square.
  if "%t1%"=="x" goto player
  if "%t1%"=="o" goto player
  set t1=x
  goto check
:2  
  if "%t2%"=="x" goto player
  if "%t2%"=="o" goto player
  set t2=x
  goto check
:3  
  if "%t3%"=="x" goto player
  if "%t3%"=="o" goto player
  set t3=x
  goto check
:4  
  if "%t4%"=="x" goto player
  if "%t4%"=="o" goto player
  set t4=x
  goto check
:5  
  if "%t5%"=="x" goto player
  if "%t5%"=="o" goto player
  set t5=x
  goto check
:6  
  if "%t6%"=="x" goto player
  if "%t6%"=="o" goto player
  set t6=x
  goto check
:7  
  if "%t7%"=="x" goto player
  if "%t7%"=="o" goto player
  set t7=x
  goto check
:8  
  if "%t8%"=="x" goto player
  if "%t8%"=="o" goto player
  set t8=x
  goto check
:9  
  if "%t9%"=="x" goto player
  if "%t9%"=="o" goto player
  set t9=x
  goto check

:COMPUTER
  set pt=o
  if "%sl%"=="1" goto skill1  
 REM (win corner to corner)
  if "%t1%"=="o" if "%t3%"=="o" if not "%t2%"=="x" if not "%t2%"=="o" goto c2
  if "%t1%"=="o" if "%t9%"=="o" if not "%t5%"=="x" if not "%t5%"=="o" goto c5
  if "%t1%"=="o" if "%t7%"=="o" if not "%t4%"=="x" if not "%t4%"=="o" goto c4  
  if "%t3%"=="o" if "%t7%"=="o" if not "%t5%"=="x" if not "%t5%"=="o" goto c5
  if "%t3%"=="o" if "%t9%"=="o" if not "%t6%"=="x" if not "%t6%"=="o" goto c6
  if "%t9%"=="o" if "%t7%"=="o" if not "%t8%"=="x" if not "%t8%"=="o" goto c8
 REM (win outside middle to outside middle)
  if "%t2%"=="o" if "%t8%"=="o" if not "%t5%"=="x" if not "%t5%"=="o" goto c5
  if "%t4%"=="o" if "%t6%"=="o" if not "%t5%"=="x" if not "%t5%"=="o" goto c5
 REM (win all others)
  if "%t1%"=="o" if "%t2%"=="o" if not "%t3%"=="x" if not "%t3%"=="o" goto c3
  if "%t1%"=="o" if "%t5%"=="o" if not "%t9%"=="x" if not "%t9%"=="o" goto c9
  if "%t1%"=="o" if "%t4%"=="o" if not "%t7%"=="x" if not "%t7%"=="o" goto c7
  if "%t2%"=="o" if "%t5%"=="o" if not "%t8%"=="x" if not "%t8%"=="o" goto c8
  if "%t3%"=="o" if "%t2%"=="o" if not "%t1%"=="x" if not "%t1%"=="o" goto c1
  if "%t3%"=="o" if "%t5%"=="o" if not "%t7%"=="x" if not "%t7%"=="o" goto c7
  if "%t3%"=="o" if "%t6%"=="o" if not "%t9%"=="x" if not "%t9%"=="o" goto c9
  if "%t4%"=="o" if "%t5%"=="o" if not "%t6%"=="x" if not "%t6%"=="o" goto c6
  if "%t6%"=="o" if "%t5%"=="o" if not "%t4%"=="x" if not "%t4%"=="o" goto c4
  if "%t7%"=="o" if "%t4%"=="o" if not "%t1%"=="x" if not "%t1%"=="o" goto c1
  if "%t7%"=="o" if "%t5%"=="o" if not "%t3%"=="x" if not "%t3%"=="o" goto c3
  if "%t7%"=="o" if "%t8%"=="o" if not "%t9%"=="x" if not "%t9%"=="o" goto c9
  if "%t8%"=="o" if "%t5%"=="o" if not "%t2%"=="x" if not "%t2%"=="o" goto c2
  if "%t9%"=="o" if "%t8%"=="o" if not "%t7%"=="x" if not "%t7%"=="o" goto c7
  if "%t9%"=="o" if "%t5%"=="o" if not "%t1%"=="x" if not "%t1%"=="o" goto c1
  if "%t9%"=="o" if "%t6%"=="o" if not "%t3%"=="x" if not "%t3%"=="o" goto c3
 REM (block general attempts) -----------------------------------------------
  if "%t1%"=="x" if "%t2%"=="x" if not "%t3%"=="x" if not "%t3%"=="o" goto c3
  if "%t1%"=="x" if "%t5%"=="x" if not "%t9%"=="x" if not "%t9%"=="o" goto c9
  if "%t1%"=="x" if "%t4%"=="x" if not "%t7%"=="x" if not "%t7%"=="o" goto c7
  if "%t2%"=="x" if "%t5%"=="x" if not "%t8%"=="x" if not "%t8%"=="o" goto c8
  if "%t3%"=="x" if "%t2%"=="x" if not "%t1%"=="x" if not "%t1%"=="o" goto c1
  if "%t3%"=="x" if "%t5%"=="x" if not "%t7%"=="x" if not "%t7%"=="o" goto c7
  if "%t3%"=="x" if "%t6%"=="x" if not "%t9%"=="x" if not "%t9%"=="o" goto c9
  if "%t4%"=="x" if "%t5%"=="x" if not "%t6%"=="x" if not "%t6%"=="o" goto c6
  if "%t6%"=="x" if "%t5%"=="x" if not "%t4%"=="x" if not "%t4%"=="o" goto c4
  if "%t7%"=="x" if "%t4%"=="x" if not "%t1%"=="x" if not "%t1%"=="o" goto c1
  if "%t7%"=="x" if "%t5%"=="x" if not "%t3%"=="x" if not "%t3%"=="o" goto c3
  if "%t7%"=="x" if "%t8%"=="x" if not "%t9%"=="x" if not "%t9%"=="o" goto c9
  if "%t8%"=="x" if "%t5%"=="x" if not "%t2%"=="x" if not "%t2%"=="o" goto c2
  if "%t9%"=="x" if "%t8%"=="x" if not "%t7%"=="x" if not "%t7%"=="o" goto c7
  if "%t9%"=="x" if "%t5%"=="x" if not "%t1%"=="x" if not "%t1%"=="o" goto c1
  if "%t9%"=="x" if "%t6%"=="x" if not "%t3%"=="x" if not "%t3%"=="o" goto c3
 REM (block obvious corner to corner) 
  if "%t1%"=="x" if "%t3%"=="x" if not "%t2%"=="x" if not "%t2%"=="o" goto c2
  if "%t1%"=="x" if "%t9%"=="x" if not "%t5%"=="x" if not "%t5%"=="o" goto c5
  if "%t1%"=="x" if "%t7%"=="x" if not "%t4%"=="x" if not "%t4%"=="o" goto c4  
  if "%t3%"=="x" if "%t7%"=="x" if not "%t5%"=="x" if not "%t5%"=="o" goto c5
  if "%t3%"=="x" if "%t9%"=="x" if not "%t6%"=="x" if not "%t6%"=="o" goto c6
  if "%t9%"=="x" if "%t7%"=="x" if not "%t8%"=="x" if not "%t8%"=="o" goto c8
  if "%sl%"=="2" goto skill2
 REM (block sneaky corner to corner 2-4, 2-6, etc.) 
  if "%t2%"=="x" if "%t4%"=="x" if not "%t1%"=="x" if not "%t1%"=="o" goto c1
  if "%t2%"=="x" if "%t6%"=="x" if not "%t3%"=="x" if not "%t3%"=="o" goto c3
  if "%t8%"=="x" if "%t4%"=="x" if not "%t7%"=="x" if not "%t7%"=="o" goto c7  
  if "%t8%"=="x" if "%t6%"=="x" if not "%t9%"=="x" if not "%t9%"=="o" goto c9
 REM (block offset corner trap 1-8, 1-6, etc.)
  if "%t1%"=="x" if "%t6%"=="x" if not "%t8%"=="x" if not "%t8%"=="o" goto c8
  if "%t1%"=="x" if "%t8%"=="x" if not "%t6%"=="x" if not "%t6%"=="o" goto c6
  if "%t3%"=="x" if "%t8%"=="x" if not "%t4%"=="x" if not "%t4%"=="o" goto c4
  if "%t3%"=="x" if "%t4%"=="x" if not "%t8%"=="x" if not "%t8%"=="o" goto c8
  if "%t9%"=="x" if "%t4%"=="x" if not "%t2%"=="x" if not "%t2%"=="o" goto c2
  if "%t9%"=="x" if "%t2%"=="x" if not "%t4%"=="x" if not "%t4%"=="o" goto c4
  if "%t7%"=="x" if "%t2%"=="x" if not "%t6%"=="x" if not "%t6%"=="o" goto c6
  if "%t7%"=="x" if "%t6%"=="x" if not "%t2%"=="x" if not "%t2%"=="o" goto c2

:SKILL2
 REM (block outside middle to outside middle)
  if "%t2%"=="x" if "%t8%"=="x" if not "%t5%"=="x" if not "%t5%"=="o" goto c5
  if "%t4%"=="x" if "%t6%"=="x" if not "%t5%"=="x" if not "%t5%"=="o" goto c5
 REM (block 3 corner trap)
  if "%t1%"=="x" if "%t9%"=="x" if not "%t2%"=="x" if not "%t2%"=="o" goto c2
  if "%t3%"=="x" if "%t7%"=="x" if not "%t2%"=="x" if not "%t2%"=="o" goto c2
  if "%t1%"=="x" if "%t9%"=="x" if not "%t4%"=="x" if not "%t4%"=="o" goto c4
  if "%t3%"=="x" if "%t7%"=="x" if not "%t4%"=="x" if not "%t4%"=="o" goto c4
  if "%t1%"=="x" if "%t9%"=="x" if not "%t6%"=="x" if not "%t6%"=="o" goto c6
  if "%t3%"=="x" if "%t7%"=="x" if not "%t6%"=="x" if not "%t6%"=="o" goto c6
  if "%t1%"=="x" if "%t9%"=="x" if not "%t8%"=="x" if not "%t8%"=="o" goto c8
  if "%t3%"=="x" if "%t7%"=="x" if not "%t8%"=="x" if not "%t8%"=="o" goto c8
:SKILL1 
 REM (just take a turn) 
  if not "%t5%"=="x" if not "%t5%"=="o" goto c5
  if not "%t1%"=="x" if not "%t1%"=="o" goto c1
  if not "%t3%"=="x" if not "%t3%"=="o" goto c3
  if not "%t7%"=="x" if not "%t7%"=="o" goto c7
  if not "%t9%"=="x" if not "%t9%"=="o" goto c9
  if not "%t2%"=="x" if not "%t2%"=="o" goto c2
  if not "%t4%"=="x" if not "%t4%"=="o" goto c4
  if not "%t6%"=="x" if not "%t6%"=="o" goto c6
  if not "%t8%"=="x" if not "%t8%"=="o" goto c8
  set nm=0
  goto update

:C1  
  set t1=o
  goto check
:C2  
  set t2=o
  goto check
:C3  
  set t3=o
  goto check
:C4  
  set t4=o
  goto check
:C5  
  set t5=o
  goto check
:C6  
  set t6=o
  goto check
:C7  
  set t7=o
  goto check
:C8  
  set t8=o
  goto check
:C9  
  set t9=o
  goto check

:CHECK
  if "%t1%"=="x" if "%t2%"=="x" if "%t3%"=="x" goto winx
  if "%t4%"=="x" if "%t5%"=="x" if "%t6%"=="x" goto winx
  if "%t7%"=="x" if "%t8%"=="x" if "%t9%"=="x" goto winx
  if "%t1%"=="x" if "%t4%"=="x" if "%t7%"=="x" goto winx
  if "%t2%"=="x" if "%t5%"=="x" if "%t8%"=="x" goto winx
  if "%t3%"=="x" if "%t6%"=="x" if "%t9%"=="x" goto winx
  if "%t1%"=="x" if "%t5%"=="x" if "%t9%"=="x" goto winx
  if "%t3%"=="x" if "%t5%"=="x" if "%t7%"=="x" goto winx
  if "%t1%"=="o" if "%t2%"=="o" if "%t3%"=="o" goto wino
  if "%t4%"=="o" if "%t5%"=="o" if "%t6%"=="o" goto wino
  if "%t7%"=="o" if "%t8%"=="o" if "%t9%"=="o" goto wino
  if "%t1%"=="o" if "%t4%"=="o" if "%t7%"=="o" goto wino
  if "%t2%"=="o" if "%t5%"=="o" if "%t8%"=="o" goto wino
  if "%t3%"=="o" if "%t6%"=="o" if "%t9%"=="o" goto wino
  if "%t1%"=="o" if "%t5%"=="o" if "%t9%"=="o" goto wino
  if "%t3%"=="o" if "%t5%"=="o" if "%t7%"=="o" goto wino
  if "%pt%"=="x" goto computer
  if "%pt%"=="o" goto update

:WINX
  set gw=x
  goto update
:WINX2
  echo   You win!
  echo   Play again (Y,N)?
  CHOICE /c:ynsq /n > nul
  if errorlevel 4 goto end
  if errorlevel 3 goto begin
  if errorlevel 2 goto end
  goto layout

:WINO
  set gw=o
  goto update
:WINO2
  echo   Sorry, You lose.
  echo   Play again (Y,N)?
  CHOICE /c:ynsq /n > nul
  if errorlevel 4 goto end
  if errorlevel 3 goto begin
  if errorlevel 2 goto end
  goto layout

:NOMOVES
  echo   There are no more moves left!
  echo   Play again (Y,N)?
  CHOICE /c:ynsq /n > nul
  if errorlevel 4 goto end
  if errorlevel 3 goto begin
  if errorlevel 2 goto end
  goto layout

:END
  cls
  echo Tic Tac Toe
  echo.
  REM Clear all variables (no spaces after equal sign).
  set gw=
  set nm=
  set sl=
  set pt=
  set t1=
  set t2=
  set t3=
  set t4=
  set t5=
  set t6=
  set t7=
  set t8=
  set t9=

Befunge

Requires an intepreter with working support for numeric input, which unfortunately excludes most online implementations.

Plays reasonably well, but not perfectly, so can be beaten.

v123456789 --- >9 >48*,:55+\-0g,1v
>9>066+0p076+0p^  ^,," |"_v#%3:- <
:,,0537051v>:#,_$#^5#,5#+<>:#v_55+
74 1098709<^+55"---+---+---"0<v520
69 04560123 >:!#v_0\1v>$2-:6%v>803
6 +0g\66++0p^   $_>#%  v#9:-1_ 6/5
5  vv5!/*88\%*28 ::g0_^>9/#v_ "I",
,,5v>5++0p82*/3-:*+\:^v,_@ >"uoY",
0+5<v0+66_v#!%2:_55v  >:^:" win!"\
1-^ g   >$>0" :evom ruoY">:#,_$v>p
\*8+ 65_^#!/*88g0** `0\!`9:::<&<^0
v   >:!67+0g:!56+0g *+*+0" :evom "
>"yM">:#,_$ :. 1234+++, 789*+ \0^<
"a s't"98:*+>:#,_$@>365*+"ward"48*
Output:
 1 | 2 | 3
---+---+---
 4 | 5 | 6
---+---+---
 7 | 8 | 9

Your move: 1

 X | 2 | 3
---+---+---
 4 | 5 | 6
---+---+---
 7 | 8 | 9

My move: 5 

 X | 2 | 3
---+---+---
 4 | O | 6
---+---+---
 7 | 8 | 9

Your move: 2

 X | X | 3
---+---+---
 4 | O | 6
---+---+---
 7 | 8 | 9

My move: 3 

 X | X | O
---+---+---
 4 | O | 6
---+---+---
 7 | 8 | 9

Your move:

C

Opening alternates between human and computer. Computer never loses.

#include <stdio.h>
#include <stdlib.h>

int b[3][3]; /* board. 0: blank; -1: computer; 1: human */

int check_winner()
{
	int i;
	for (i = 0; i < 3; i++) {
		if (b[i][0] && b[i][1] == b[i][0] && b[i][2] == b[i][0])
			return b[i][0];
		if (b[0][i] && b[1][i] == b[0][i] && b[2][i] == b[0][i])
			return b[0][i];
	}
	if (!b[1][1]) return 0;

	if (b[1][1] == b[0][0] && b[2][2] == b[0][0]) return b[0][0];
	if (b[1][1] == b[2][0] && b[0][2] == b[1][1]) return b[1][1];

	return 0;
}

void showboard()
{
	const char *t = "X O";
	int i, j;
	for (i = 0; i < 3; i++, putchar('\n'))
		for (j = 0; j < 3; j++)
			printf("%c ", t[ b[i][j] + 1 ]);
	printf("-----\n");
}

#define for_ij for (i = 0; i < 3; i++) for (j = 0; j < 3; j++)
int best_i, best_j;
int test_move(int val, int depth)
{
	int i, j, score;
	int best = -1, changed = 0;

	if ((score = check_winner())) return (score == val) ? 1 : -1;

	for_ij {
		if (b[i][j]) continue;

		changed = b[i][j] = val;
		score = -test_move(-val, depth + 1);
		b[i][j] = 0;

		if (score <= best) continue;
		if (!depth) {
			best_i = i;
			best_j = j;
		}
		best = score;
	}

	return changed ? best : 0;
}

const char* game(int user)
{
	int i, j, k, move, win = 0;
	for_ij b[i][j] = 0;

	printf("Board postions are numbered so:\n1 2 3\n4 5 6\n7 8 9\n");
	printf("You have O, I have X.\n\n");
	for (k = 0; k < 9; k++, user = !user) {
		while(user) {
			printf("your move: ");
			if (!scanf("%d", &move)) {
				scanf("%*s");
				continue;
			}
			if (--move < 0 || move >= 9) continue;
			if (b[i = move / 3][j = move % 3]) continue;

			b[i][j] = 1;
			break;
		}
		if (!user) {
			if (!k) { /* randomize if computer opens, less boring */
				best_i = rand() % 3;
				best_j = rand() % 3;
			} else
				test_move(-1, 0);

			b[best_i][best_j] = -1;
			printf("My move: %d\n", best_i * 3 + best_j + 1);
		}

		showboard();
		if ((win = check_winner())) 
			return win == 1 ? "You win.\n\n": "I win.\n\n";
	}
	return "A draw.\n\n";
}

int main()
{
	int first = 0;
	while (1) printf("%s", game(first = !first));
	return 0;
}

C#

This implementation is purposely wordy because Tic-Tac-Toe is often a starting level program.
It tries to show a number of C# code features while still keeping each function small and understandable.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace RosettaTicTacToe
{
  class Program
  {

    /*================================================================
     *Pieces (players and board)
     *================================================================*/
    static string[][] Players = new string[][] { 
      new string[] { "COMPUTER", "X" }, // computer player
      new string[] { "HUMAN", "O" }     // human player
    };

    const int Unplayed = -1;
    const int Computer = 0;
    const int Human = 1;

    // GameBoard holds index into Players[] (0 or 1) or Unplayed (-1) if location not yet taken
    static int[] GameBoard = new int[9];

    static int[] corners = new int[] { 0, 2, 6, 8 };

    static int[][] wins = new int[][] { 
      new int[] { 0, 1, 2 }, new int[] { 3, 4, 5 }, new int[] { 6, 7, 8 }, 
      new int[] { 0, 3, 6 }, new int[] { 1, 4, 7 }, new int[] { 2, 5, 8 }, 
      new int[] { 0, 4, 8 }, new int[] { 2, 4, 6 } };


    /*================================================================
     *Main Game Loop (this is what runs/controls the game)
     *================================================================*/
    static void Main(string[] args)
    {
      while (true)
      {
        Console.Clear();
        Console.WriteLine("Welcome to Rosetta Code Tic-Tac-Toe for C#.");
        initializeGameBoard();
        displayGameBoard();
        int currentPlayer = rnd.Next(0, 2);  // current player represented by Players[] index of 0 or 1
        Console.WriteLine("The first move goes to {0} who is playing {1}s.\n", playerName(currentPlayer), playerToken(currentPlayer));
        while (true)
        {
          int thisMove = getMoveFor(currentPlayer);
          if (thisMove == Unplayed)
          {
            Console.WriteLine("{0}, you've quit the game ... am I that good?", playerName(currentPlayer));
            break;
          }
          playMove(thisMove, currentPlayer);
          displayGameBoard();
          if (isGameWon())
          {
            Console.WriteLine("{0} has won the game!", playerName(currentPlayer));
            break;
          }
          else if (isGameTied())
          {
            Console.WriteLine("Cat game ... we have a tie.");
            break;
          }
          currentPlayer = getNextPlayer(currentPlayer);
        }
        if (!playAgain())
          return;
      }
    }

    /*================================================================
     *Move Logic
     *================================================================*/
    static int getMoveFor(int player)
    {
      if (player == Human)
        return getManualMove(player);
      else
      {
        //int selectedMove = getManualMove(player);
        //int selectedMove = getRandomMove(player);
        int selectedMove = getSemiRandomMove(player);
        //int selectedMove = getBestMove(player);
        Console.WriteLine("{0} selects position {1}.", playerName(player), selectedMove + 1);
        return selectedMove;
      }
    }

    static int getManualMove(int player)
    {
      while (true)
      {
        Console.Write("{0}, enter you move (number): ", playerName(player));
        ConsoleKeyInfo keyInfo = Console.ReadKey();
        Console.WriteLine();  // keep the display pretty
        if (keyInfo.Key == ConsoleKey.Escape)
          return Unplayed;
        if (keyInfo.Key >= ConsoleKey.D1 && keyInfo.Key <= ConsoleKey.D9)
        {
          int move = keyInfo.KeyChar - '1';  // convert to between 0..8, a GameBoard index position.
          if (GameBoard[move] == Unplayed)
            return move;
          else
            Console.WriteLine("Spot {0} is already taken, please select again.", move + 1);
        }
        else
          Console.WriteLine("Illegal move, please select again.\n");
      }
    }

    static int getRandomMove(int player)
    {
      int movesLeft = GameBoard.Count(position => position == Unplayed);
      int x = rnd.Next(0, movesLeft);
      for (int i = 0; i < GameBoard.Length; i++)  // walk board ...
      {
        if (GameBoard[i] == Unplayed && x < 0)    // until we reach the unplayed move.
          return i;
        x--;
      }
      return Unplayed;
    }

    // plays random if no winning move or needed block.
    static int getSemiRandomMove(int player)
    {
      int posToPlay;
      if (checkForWinningMove(player, out posToPlay))
        return posToPlay;
      if (checkForBlockingMove(player, out posToPlay))
        return posToPlay;
      return getRandomMove(player);
    }

    // purposely not implemented (this is the thinking part).
    static int getBestMove(int player)
    {
      return -1;
    }

    static bool checkForWinningMove(int player, out int posToPlay)
    {
      posToPlay = Unplayed;
      foreach (var line in wins)
        if (twoOfThreeMatchPlayer(player, line, out posToPlay))
          return true;
      return false;
    }

    static bool checkForBlockingMove(int player, out int posToPlay)
    {
      posToPlay = Unplayed;
      foreach (var line in wins)
        if (twoOfThreeMatchPlayer(getNextPlayer(player), line, out posToPlay))
          return true;
      return false;
    }

    static bool twoOfThreeMatchPlayer(int player, int[] line, out int posToPlay)
    {
      int cnt = 0;
      posToPlay = int.MinValue;
      foreach (int pos in line)
      {
        if (GameBoard[pos] == player)
          cnt++;
        else if (GameBoard[pos] == Unplayed)
          posToPlay = pos;
      }
      return cnt == 2 && posToPlay >= 0;
    }

    static void playMove(int boardPosition, int player)
    {
      GameBoard[boardPosition] = player;
    }

    static bool isGameWon()
    {
      return wins.Any(line => takenBySamePlayer(line[0], line[1], line[2]));
    }

    static bool takenBySamePlayer(int a, int b, int c)
    {
      return GameBoard[a] != Unplayed && GameBoard[a] == GameBoard[b] && GameBoard[a] == GameBoard[c];
    }

    static bool isGameTied()
    {
      return !GameBoard.Any(spot => spot == Unplayed);
    }

    /*================================================================
     *Misc Methods
     *================================================================*/
    static Random rnd = new Random();

    static void initializeGameBoard()
    {
      for (int i = 0; i < GameBoard.Length; i++)
        GameBoard[i] = Unplayed;
    }

    static string playerName(int player)
    {
      return Players[player][0];
    }

    static string playerToken(int player)
    {
      return Players[player][1];
    }

    static int getNextPlayer(int player)
    {
      return (player + 1) % 2;
    }

    static void displayGameBoard()
    {
      Console.WriteLine(" {0} | {1} | {2}", pieceAt(0), pieceAt(1), pieceAt(2));
      Console.WriteLine("---|---|---");
      Console.WriteLine(" {0} | {1} | {2}", pieceAt(3), pieceAt(4), pieceAt(5));
      Console.WriteLine("---|---|---");
      Console.WriteLine(" {0} | {1} | {2}", pieceAt(6), pieceAt(7), pieceAt(8));
      Console.WriteLine();
    }

    static string pieceAt(int boardPosition)
    {
      if (GameBoard[boardPosition] == Unplayed)
        return (boardPosition + 1).ToString();  // display 1..9 on board rather than 0..8
      return playerToken(GameBoard[boardPosition]);
    }

    private static bool playAgain()
    {
      Console.WriteLine("\nDo you want to play again?");
      return Console.ReadKey(false).Key == ConsoleKey.Y;
    }
  }

}
Output:
Welcome to Rosetta Code Tic-Tac-Toe for C#.
 1 | 2 | 3
---|---|---
 4 | 5 | 6
---|---|---
 7 | 8 | 9

The first move goes to HUMAN who is playing Os.

HUMAN, enter you move (number): 5
 1 | 2 | 3
---|---|---
 4 | O | 6
---|---|---
 7 | 8 | 9

COMPUTER selects position 7.
 1 | 2 | 3
---|---|---
 4 | O | 6
---|---|---
 X | 8 | 9

HUMAN, enter you move (number): 0
Illegal move, please select again.

HUMAN, enter you move (number): 1
 O | 2 | 3
---|---|---
 4 | O | 6
---|---|---
 X | 8 | 9

COMPUTER selects position 9.
 O | 2 | 3
---|---|---
 4 | O | 6
---|---|---
 X | 8 | X

HUMAN, enter you move (number):

C++

#include <windows.h>
#include <iostream>
#include <string>

//--------------------------------------------------------------------------------------------------
using namespace std;

//--------------------------------------------------------------------------------------------------
enum players { Computer, Human, Draw, None };
const int iWin[8][3] = { { 0, 1, 2 }, { 3, 4, 5 }, { 6, 7, 8 }, { 0, 3, 6 }, { 1, 4, 7 }, { 2, 5, 8 }, { 0, 4, 8 }, { 2, 4, 6 } };

//--------------------------------------------------------------------------------------------------
class ttt
{
public:
    ttt() { _p = rand() % 2; reset(); }

    void play()
    {
	int res = Draw;
	while( true )
	{
	    drawGrid();
	    while( true )
	    {
		if( _p ) getHumanMove();
		else getComputerMove();

		drawGrid();

		res = checkVictory();
		if( res != None ) break;

		++_p %= 2;
	    }

	    if( res == Human ) cout << "CONGRATULATIONS HUMAN --- You won!";
	    else if( res == Computer ) cout << "NOT SO MUCH A SURPRISE --- I won!";
	    else cout << "It's a draw!";

	    cout << endl << endl;

	    string r;
	    cout << "Play again( Y / N )? "; cin >> r;
	    if( r != "Y" && r != "y" ) return;

	    ++_p %= 2;
	    reset();

	}
    }

private:
    void reset() 
    {
	for( int x = 0; x < 9; x++ )
	    _field[x] = None;
    }

    void drawGrid()
    {
	system( "cls" );
		
        COORD c = { 0, 2 };
	SetConsoleCursorPosition( GetStdHandle( STD_OUTPUT_HANDLE ), c );

	cout << " 1 | 2 | 3 " << endl;
	cout << "---+---+---" << endl;
	cout << " 4 | 5 | 6 " << endl;
	cout << "---+---+---" << endl;
	cout << " 7 | 8 | 9 " << endl << endl << endl;

	int f = 0;
	for( int y = 0; y < 5; y += 2 )
	    for( int x = 1; x < 11; x += 4 )
	    {
		if( _field[f] != None )
		{
		    COORD c = { x, 2 + y };
		    SetConsoleCursorPosition( GetStdHandle( STD_OUTPUT_HANDLE ), c );
		    string o = _field[f] == Computer ? "X" : "O";
		    cout << o;
		}
		f++;
	    }

        c.Y = 9;
	SetConsoleCursorPosition( GetStdHandle( STD_OUTPUT_HANDLE ), c );
    }

    int checkVictory()
    {
	for( int i = 0; i < 8; i++ )
	{
	    if( _field[iWin[i][0]] != None &&
		_field[iWin[i][0]] == _field[iWin[i][1]] && _field[iWin[i][1]] == _field[iWin[i][2]] )
	    {
		return _field[iWin[i][0]];
	    }
	}

	int i = 0;
	for( int f = 0; f < 9; f++ )
	{
	    if( _field[f] != None )
		i++;
	}
	if( i == 9 ) return Draw;

	return None;
    }

    void getHumanMove()
    {
	int m;
	cout << "Enter your move ( 1 - 9 ) ";
	while( true )
	{
	    m = 0;
	    do
	    { cin >> m; }
	    while( m < 1 && m > 9 );

	    if( _field[m - 1] != None )
		cout << "Invalid move. Try again!" << endl;
	    else break;
	}

	_field[m - 1] = Human;
    }

    void getComputerMove()
    {
	int move = 0;

	do{ move = rand() % 9; }
	while( _field[move] != None );

	for( int i = 0; i < 8; i++ )
	{
	    int try1 = iWin[i][0], try2 = iWin[i][1], try3 = iWin[i][2];

	    if( _field[try1] != None && _field[try1] == _field[try2] && _field[try3] == None )
	    {
		move = try3;
		if( _field[try1] == Computer ) break;
	    }

	    if( _field[try1] != None && _field[try1] == _field[try3] && _field[try2] == None ) 
	    {			
		move = try2;
		if( _field[try1] == Computer ) break;
	    }

	    if( _field[try2] != None && _field[try2] == _field[try3] && _field[try1] == None )
	    {
		move = try1;
		if( _field[try2] == Computer ) break;
	    }
        }
	_field[move] = Computer;
		
    }


int _p;
int _field[9];
};
//--------------------------------------------------------------------------------------------------
int main( int argc, char* argv[] )
{
    srand( GetTickCount() );

    ttt tic;
    tic.play();

    return 0;
}
//--------------------------------------------------------------------------------------------------
Output:

Computer plays 'X' and human plays 'O'

 1 | 2 | X
---+---+---
 X | 5 | 6
---+---+---
 7 | O | 9

Enter your move ( 1 - 9 )

Common Lisp

(defun generate-board ()
  (loop repeat 9 collect nil))

(defparameter *straights* '((1 2 3) (4 5 6) (7 8 9) (1 4 7) (2 5 8) (3 6 9) (1 5 9) (3 5 7)))
(defparameter *current-player* 'x)

(defun get-board-elt (n board)
  (nth (1- n) board))

(defun legal-p (n board)
  (null (get-board-elt n board)))

(defun set-board-elt (n board symbol)
  (if (legal-p n board)
      (setf (nth (1- n) board) symbol)
      (progn (format t "Illegal move. Try again.~&")
	     (set-board-elt (read) board symbol))))

(defun list-legal-moves (board)
  (loop for i from 1 to (length board)
     when (legal-p i board)
     collect i))

(defun get-random-element (lst)
  (nth (random (length lst)) lst))

(defun multi-non-nil-eq (lst)
  (and (notany #'null lst)
       (notany #'null (mapcar #'(lambda (x) (eq (car lst) x)) lst))
       (car lst)))
	
(defun elements-of-straights (board)
  (loop for i in *straights*
     collect (loop for j from 0 to 2
	   collect (get-board-elt (nth j i) board))))

(defun find-winner (board)
  (car (remove-if #'null (mapcar #'multi-non-nil-eq (elements-of-straights board)))))

(defun set-player (mark)
  (format t "Shall a computer play as ~a? (y/n)~&" mark)
  (let ((response (read)))
    (cond ((equalp response 'y) t)
	  ((equalp response 'n) nil)
	  (t (format t "Come again?~&")
	     (set-player mark)))))

(defun player-move (board symbol)
  (format t "~%Player ~a, please input your move.~&" symbol)
  (set-board-elt (read) board symbol)
  (format t "~%"))

(defun computer-move (board symbol)
  (let ((move (get-random-element (list-legal-moves board))))
    (set-board-elt move board symbol)
    (format t "~%computer selects ~a~%~%" move)))

(defun computer-move-p (current-player autoplay-x-p autoplay-o-p)
  (if (eq current-player 'x)
      autoplay-x-p
      autoplay-o-p))

(defun perform-turn (current-player board autoplay-x-p autoplay-o-p)
  (if (computer-move-p current-player autoplay-x-p autoplay-o-p)
      (computer-move board current-player)
      (player-move board current-player)))

(defun switch-player ()
  (if (eq *current-player* 'x) 
      (setf *current-player* 'o)
      (setf *current-player* 'x)))

(defun display-board (board)
  (loop for i downfrom 2 to 0
     do (loop for j from 1 to 3
	   initially (format t "|")
	   do (format t "~a|" (or (get-board-elt (+ (* 3 i) j) board) (+ (* 3 i) j)))
	   finally (format t "~&"))))

(defun tic-tac-toe ()
  (setf *current-player* 'x)
  (let ((board (generate-board))
	(autoplay-x-p (set-player 'x))
	(autoplay-o-p (set-player 'o)))
    (format t "~%")
    (loop until (or (find-winner board) (null (list-legal-moves board)))
       do (display-board board)      
       do (perform-turn *current-player* board autoplay-x-p autoplay-o-p)
       do (switch-player)
       finally (if (find-winner board)
		   (format t "The winner is ~a!" (find-winner board))
		   (format t "It's a tie.")))))
Output:
CL-USER> (tic-tac-toe)
Shall a computer play as X? (y/n)
n
Shall a computer play as O? (y/n)
y

|7|8|9|
|4|5|6|
|1|2|3|

Player X, please input your move.
5

|7|8|9|
|4|X|6|
|1|2|3|

computer selects 8

|7|O|9|
|4|X|6|
|1|2|3|

Player X, please input your move.

D

import std.stdio, std.string, std.algorithm, std.conv, std.random,
       std.ascii, std.array, std.range, std.math;

struct GameBoard {
    dchar[9] board = "123456789";
    enum : dchar { human = 'X', computer = 'O' }
    enum Game { going, humanWins, computerWins, draw }

    const pure nothrow @safe @nogc invariant() {
        int nHuman = 0, nComputer = 0;
        foreach (immutable i, immutable c; board)
            if (c.isDigit)
                assert(i == c - '1'); // In correct position?
            else {
                assert(c == human || c == computer);
                (c == human ? nHuman : nComputer)++;
            }
        assert(abs(nHuman - nComputer) <= 1);
    }

    string toString() const pure {
        return format("%(%-(%s|%)\n-+-+-\n%)", board[].chunks(3));
    }

    bool isAvailable(in int i) const pure nothrow @safe @nogc {
        return i >= 0 && i < 9 && board[i].isDigit;
    }

    auto availablePositions() const pure nothrow @safe /*@nogc*/ {
        return 9.iota.filter!(i => isAvailable(i));
    }

    Game winner() const pure nothrow @safe /*@nogc*/ {
        static immutable wins = [[0, 1, 2], [3, 4, 5], [6, 7, 8],
                                 [0, 3, 6], [1, 4, 7], [2, 5, 8],
                                 [0, 4, 8], [2, 4, 6]];

        foreach (immutable win; wins) {
            immutable bw0 = board[win[0]];
            if (bw0.isDigit)
                continue; // Nobody wins on this one.

            if (bw0 == board[win[1]] && bw0 == board[win[2]])
                return bw0 == GameBoard.human ?
                              Game.humanWins :
                              Game.computerWins;
        }

        return availablePositions.empty ? Game.draw: Game.going;
    }

    bool isFinished() const pure nothrow @safe /*@nogc*/ {
        return winner != Game.going;
    }

    int computerMove() const // Random move.
    out(res) {
        assert(res >= 0 && res < 9 && isAvailable(res));
    } body {
        // return availablePositions.array.choice;
        return availablePositions.array[uniform(0, $)];
    }
}


GameBoard playGame() {
    GameBoard board;
    bool playsHuman = true;

    while (!board.isFinished) {
        board.writeln;

        int move;
        if (playsHuman) {
            do {
                writef("Your move (available moves: %s)? ",
                       board.availablePositions.map!q{ a + 1 });
                readf("%d\n", &move);
                move--; // Zero based indexing.
                if (move < 0)
                    return board;
            } while (!board.isAvailable(move));
        } else
            move = board.computerMove;

        assert(board.isAvailable(move));
        writefln("\n%s chose %d", playsHuman ? "You" : "I", move + 1);
        board.board[move] = playsHuman ? GameBoard.human :
                                         GameBoard.computer;
        playsHuman = !playsHuman; // Switch player.
    }

    return board;
}


void main() {
    "Tic-tac-toe game player.\n".writeln;
    immutable outcome = playGame.winner;

    final switch (outcome) {
        case GameBoard.Game.going:
            "Game stopped.".writeln;
            break;
        case GameBoard.Game.humanWins:
            "\nYou win!".writeln;
            break;
        case GameBoard.Game.computerWins:
            "\nI win.".writeln;
            break;
        case GameBoard.Game.draw:
            "\nDraw".writeln;
            break;
    }
}
Output:
Tic-tac-toe game player.

1|2|3
-+-+-
4|5|6
-+-+-
7|8|9
Your move (available moves: [1, 2, 3, 4, 5, 6, 7, 8, 9])? 1

You chose 1
X|2|3
-+-+-
4|5|6
-+-+-
7|8|9

I chose 2
X|O|3
-+-+-
4|5|6
-+-+-
7|8|9
Your move (available moves: [3, 4, 5, 6, 7, 8, 9])? 5

You chose 5
X|O|3
-+-+-
4|X|6
-+-+-
7|8|9

I chose 3
X|O|O
-+-+-
4|X|6
-+-+-
7|8|9
Your move (available moves: [4, 6, 7, 8, 9])? 9

You chose 9

You win!

Delphi

Works with: Delphi version 6.0

This is a GUI, event driven version of the game. The game board is a "TStringGrid" component, which has a grid that can hold and display characters. In this case, the grid displays Xs and Ox using a large font.

When the user clicks on the grid, this generates an event that is handled by the program. The mouse click coordinates are converted to a cell coordinates and a large X is placed in the box. At this point program tests if this resulted in a win. Next it calculate the computer's response and it checks to see if the computer won. The process is repeated until there is a winner or a draw.

{Array contain possiple winning lines}

type TWinLine = array [0..3-1] of TPoint;

var WinLines: array [0..8-1] of TWinLine = (
((X:0; Y:0), (X:1; Y:0), (X:2; Y:0)),
((X:0; Y:1), (X:1; Y:1), (X:2; Y:1)),
((X:0; Y:2), (X:1; Y:2), (X:2; Y:2)),
((X:0; Y:0), (X:0; Y:1), (X:0; Y:2)),
((X:1; Y:0), (X:1; Y:1), (X:1; Y:2)),
((X:2; Y:0), (X:2; Y:1), (X:2; Y:2)),
((X:0; Y:0), (X:1; Y:1), (X:2; Y:2)),
((X:2; Y:0), (X:1; Y:1), (X:0; Y:2))
);


{Array containing all characters in a line}

type TCellArray = array [0..3-1] of char;

var WinLineInx: integer;
var GameOver: boolean;

procedure ClearGrid;
{Clear TTT Grid by setting all cells to a space}
var X,Y: integer;
begin
with TicTacToeDlg do
 begin
 for Y:=0 to GameGrid.RowCount-1 do
  for X:=0 to GameGrid.ColCount-1 do GameGrid.Cells[X,Y]:=' ';
 WinLineInx:=-1;
 Status1Dis.Caption:='';
 GameOver:=False;
 end;

end;


function FirstEmptyCell(var P: TPoint): boolean;
{Find first empty grid i.e. the one containing a space}
{Returns false if there are no empty cells (a tie game)}
var X,Y: integer;
begin
Result:=True;
with TicTacToeDlg do
 begin
 {Iterate through all cells in array}
 for Y:=0 to GameGrid.RowCount-1 do
  for X:=0 to GameGrid.ColCount-1 do
   if GameGrid.Cells[X,Y]=' ' then
	begin
	P.X:=X; P.Y:=Y;
	Exit;
	end;
 end;
Result:=False;
end;



procedure GetLineChars(Inx: integer; var CA: TCellArray);
{Get all the characters in a specific win line}
var P1,P2,P3: TPoint;
begin
with TicTacToeDlg do
 begin
 {Get cell position of specific win line}
 P1:=WinLines[Inx,0];
 P2:=WinLines[Inx,1];
 P3:=WinLines[Inx,2];
 {Get the characters from each and put in array}
 CA[0]:=GameGrid.Cells[P1.X,P1.Y][1];
 CA[1]:=GameGrid.Cells[P2.X,P2.Y][1];
 CA[2]:=GameGrid.Cells[P3.X,P3.Y][1];
 end;
end;



function IsWinner(var Inx: integer; var C: char): boolean;
{Test if the specified line is a winner}
{Return index of line and the char of winner}
var I,J: integer;
var CA: TCellArray;
begin
with TicTacToeDlg do
 begin
 Result:=False;
 {Go through all winning patterns}
 for J:=0 to High(WinLines) do
	begin
	{Get one winning pattern}
	GetLineChars(J,CA);
	{Look for line that has the same char in all three places}
	if (CA[0]<>' ') and (CA[0]=CA[1]) and (CA[0]=CA[2]) then
		begin
		Result:=True;
		Inx:=J;
		C:=CA[0];
		end;
	end;

 end;
end;


procedure DrawWinLine(Inx: integer);
{Draw line through winning squares}
var Line: TWinLine;
var C1,C2: TPoint;
var P1,P2: TPoint;
var W2,H2: integer;
begin
with TicTacToeDlg do
 begin
 {Offset to center of cell}
 W2:=GameGrid.ColWidths[0] div 2;
 H2:=GameGrid.RowHeights[0] div 2;
 {Get winning pattern of lines}
 Line:=WinLines[Inx];
 {Get beginning and ending cell of win}
 C1:=Line[0]; C2:=Line[2];
 {Convert to screen coordinates}
 P1.X:=C1.X * GameGrid.ColWidths[0] + W2;
 P1.Y:=C1.Y * GameGrid.RowHeights[0] + H2;
 P2.X:=C2.X * GameGrid.ColWidths[0] + W2;
 P2.Y:=C2.Y * GameGrid.RowHeights[0] + H2;
 {Set line attributes}
 GameGrid.Canvas.Pen.Color:=clRed;
 GameGrid.Canvas.Pen.Width:=5;
 {Draw line}
 GameGrid.Canvas.MoveTo(P1.X,P1.Y);
 GameGrid.Canvas.LineTo(P2.X,P2.Y);
 end;
end;



procedure DoBestComputerMove;
{Analyze game board and execute the best computer move}
var I,J,Inx: integer;
var CA: TCellArray;
var P: TPoint;


	function UrgentMove(CA: TCellArray; var EmptyInx: integer): boolean;
	{Test row, column or diagonal for  an urgent move}
	{This would be either an immediate win or immediate loss}
	{Returns True if there is an urgent move and the index of location to respond}
	var I: integer;
	var OCnt,XCnt,EmptyCnt: integer;
	begin
	Result:=False;
	OCnt:=0; XCnt:=0;
	EmptyCnt:=0; EmptyInx:=-1;
	{Count number of Xs, Os or Spaces in line}
	for I:=0 to High(CA) do
		begin
		case CA[I] of
		 'O': Inc(OCnt);
		 'X': Inc(XCnt);
		 ' ':
		 	begin
		 	Inc(EmptyCnt);
		 	if EmptyCnt=1 then EmptyInx:=I;
		 	end;
		 end;
		end;
	{Look for pattern of one empty and two Xs or two Os}
	{Which means it's one move away from a win}
	Result:=(EmptyCnt=1) and ((OCnt=2) or (XCnt=2));
	end;


begin
with TicTacToeDlg do
 begin
 {Look for urgent moves in all patterns of wins}
 for J:=0 to High(WinLines) do
	begin
	{Get a winning pattern of chars}
	GetLineChars(J,CA);
	if UrgentMove(CA,Inx) then
		begin
		{Urgent move found - take it}
		P:=WinLines[J,Inx];
                GameGrid.Cells[P.X,P.Y]:='O';
		exit;
		end;
	end;
 {No urgent moves, so use first empty}
 {If there is no empty, the game is stalemated}
 if FirstEmptyCell(P) then GameGrid.Cells[P.X,P.Y]:='O';
 end;
end;


function TestWin: boolean;
{Test if last move resulted in win/draw}
var Inx: integer; var C: char;
var P: TPoint;
var S: string;
begin
Result:=True;
{Test if somebody won}
if IsWinner(Inx,C) then
	begin
	WinLineInx:=Inx;
	TicTacToeDlg.GameGrid.Invalidate;
	if C='O' then S:=' Computer Won!!' else S:=' You Won!!';
        TicTacToeDlg.Status1Dis.Caption:=S;
	GameOver:=True;
	exit;
	end;
{Test if game is a draw}
if not FirstEmptyCell(P) then
	begin
        TicTacToeDlg.Status1Dis.Caption:=' Game is Draw.';
	GameOver:=True;
	exit;
	end;
Result:=False;
end;


procedure PlayTicTacToe;
{Show TicTacToe dialog box}
begin
ClearGrid;
TicTacToeDlg.ShowModal
end;



procedure TTicTacToeDlg.GameGridMouseDown(Sender: TObject;
  Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
{Handle user click on TicTacToe grid}
var Row,Col: integer;
begin
with TicTacToeDlg do
 begin
 if GameOver then exit;;
 {Convert Mouse X,Y to Grid row and column}
 GameGrid.MouseToCell(X,Y,Col,Row);
 {Mark user's selection by placing X in the cell}
 if GameGrid.Cells[Col,Row]=' 'then
    GameGrid.Cells[Col,Row]:='X';
 {Did this result in a win? }
 if TestWin then exit;
 {Get computer's response}
 DoBestComputerMove;
 {Did computer win}
 TestWin;
 end;
end;

procedure TTicTacToeDlg.ReplayBtnClick(Sender: TObject);
begin
ClearGrid;
end;



procedure TTicTacToeDlg.GameGridDrawCell(Sender: TObject; ACol,
  ARow: Integer; Rect: TRect; State: TGridDrawState);
{Draw winner line on top of Xs and Os}
begin
if WinLineInx>=0 then DrawWinLine(WinLineInx);
end;
Output:

Elapsed Time: 19.126 Sec.

EasyLang

It uses minimax with alpha-beta pruning. Therefore, the computer never loses.

Run it

len f[] 9
state = 0
textsize 14
#
proc init . .
   linewidth 2
   clear
   color 666
   move 34 96
   line 34 20
   move 62 96
   line 62 20
   move 10 72
   line 86 72
   move 10 44
   line 86 44
   linewidth 2.5
   for i = 1 to 9
      f[i] = 0
   .
   if state = 1
      timer 0.2
   .
.
proc draw ind . .
   c = (ind - 1) mod 3
   r = (ind - 1) div 3
   x = c * 28 + 20
   y = r * 28 + 30
   if f[ind] = 4
      color 900
      move x - 7 y - 7
      line x + 7 y + 7
      move x + 7 y - 7
      line x - 7 y + 7
   elif f[ind] = 1
      color 009
      move x y
      circle 10
      color -2
      circle 7.5
   .
.
proc sum3 a d . st .
   for i = 1 to 3
      s += f[a]
      a += d
   .
   if s = 3
      st = -1
   elif s = 12
      st = 1
   .
.
proc rate . res done .
   res = 0
   for i = 1 step 3 to 7
      sum3 i 1 res
   .
   for i = 1 to 3
      sum3 i 3 res
   .
   sum3 1 4 res
   sum3 3 2 res
   cnt = 1
   for i = 1 to 9
      if f[i] = 0
         cnt += 1
      .
   .
   res *= cnt
   done = 1
   if res = 0 and cnt > 1
      done = 0
   .
.
proc minmax player alpha beta . rval rmov .
   rate rval done
   if done = 1
      if player = 1
         rval = -rval
      .
   else
      rval = alpha
      start = randint 9
      mov = start
      repeat
         if f[mov] = 0
            f[mov] = player
            minmax (5 - player) (-beta) (-rval) val h
            val = -val
            f[mov] = 0
            if val > rval
               rval = val
               rmov = mov
            .
         .
         mov = mov mod 9 + 1
         until mov = start or rval >= beta
      .
   .
.
proc show_result val . .
   color 555
   move 16 4
   if val < 0
      # this never happens
      text "You won"
   elif val > 0
      text "You lost"
   else
      text "Tie"
   .
   state += 2
.
proc computer . .
   minmax 4 -11 11 val mov
   f[mov] = 4
   draw mov
   rate val done
   state = 0
   if done = 1
      show_result val
   .
.
proc human . .
   mov = floor ((mouse_x - 6) / 28) + 3 * floor ((mouse_y - 16) / 28) + 1
   if f[mov] = 0
      f[mov] = 1
      draw mov
      state = 1
      timer 0.5
   .
.
on timer
   rate val done
   if done = 1
      show_result val
   else
      computer
   .
.
on mouse_down
   if state = 0
      if mouse_x > 6 and mouse_x < 90 and mouse_y > 16
         human
      .
   elif state >= 2
      state -= 2
      init
   .
.
init

Erlang

The program will randomly chose if the computer ("X") or the user ("O") starts. The computer look ahead is only one level. Perhaps the computer might lose?

-module(tic_tac_toe).

-export( [task/0] ).

task() -> io:fwrite( "Result: ~p.~n", [turn(player(random:uniform()), board())] ).



board() -> [{X, erlang:integer_to_list(X)} || X <- lists:seq(1, 9)].

board_tuples( Selections, Board ) -> [lists:keyfind(X, 1, Board) || X <- Selections].

computer_move( Player, Board ) ->
	[N | _T] = lists:flatten( [X(Player, Board) || X <- [fun computer_move_win/2, fun computer_move_block/2, fun computer_move_middle/2, fun computer_move_random/2]] ),
	N.

computer_move_block( Player, Board ) ->	computer_move_two_same_player( player(false, Player), Board ).

computer_move_middle( _Player, Board ) ->
	{5, Y} = lists:keyfind( 5, 1, Board ),
	computer_move_middle( is_empty(Y) ).

computer_move_middle( true ) -> [5];
computer_move_middle( false ) -> [].

computer_move_random( _Player, Board ) ->
	Ns = [X || {X, Y} <- Board, is_empty(Y)],
	[lists:nth( random:uniform(erlang:length(Ns)), Ns )].

computer_move_two_same_player( Player, Board ) ->
        Selections = [X || X <- three_in_row_all(), is_two_same_player(Player, X, Board)],
	computer_move_two_same_player( Player, Board, Selections ).

computer_move_two_same_player( _Player, _Board, [] ) -> [];
computer_move_two_same_player( _Player, Board, [Selection | _T] ) -> [X || {X, Y} <- board_tuples(Selection, Board), is_empty(Y)].

computer_move_win( Player, Board ) -> computer_move_two_same_player( Player, Board ).

is_empty( Square ) -> Square =< "9". % Do not use < "10".

is_finished( Board ) -> is_full( Board ) orelse is_three_in_row( Board ).

is_full( Board ) -> [] =:= [X || {X, Y} <- Board, is_empty(Y)].

is_three_in_row( Board ) ->
	Fun = fun(Selections) -> is_three_in_row_same_player( board_tuples(Selections, Board) ) end,
	lists:any( Fun, three_in_row_all() ).

is_three_in_row_same_player( Selected ) -> three_in_row_player( Selected ) =/= no_player.

is_two_same_player( Player, Selections, Board ) -> is_two_same_player( Player, [{X, Y} || {X, Y} <- board_tuples(Selections, Board), not is_empty(Y)] ).

is_two_same_player( Player, [{_X, Player}, {_Y, Player}] ) -> true;
is_two_same_player( _Player, _Selected ) -> false.

player( Random ) when Random > 0.5 -> "O";
player( _Random ) -> "X".

player( true, _Player ) -> finished;
player( false, "X" ) -> "O";
player( false, "O" ) -> "X".

result( Board ) -> result( is_full(Board), Board ).

result( true, _Board ) -> draw;
result( false, Board ) ->
	[Winners] = [Selections || Selections <- three_in_row_all(), three_in_row_player(board_tuples(Selections, Board)) =/= no_player],
	"Winner is " ++ three_in_row_player( board_tuples(Winners, Board) ).

three_in_row_all() -> three_in_row_horisontal() ++ three_in_row_vertical() ++ three_in_row_diagonal().
three_in_row_diagonal() -> [[1,5,9], [3,5,7]].
three_in_row_horisontal() -> [[1,2,3], [4,5,6], [7,8,9]].
three_in_row_vertical() -> [[1,4,7], [2,5,8], [3,6,9]].

three_in_row_player( [{_X, Player}, {_Y, Player}, {_Z, Player}] ) -> three_in_row_player( not is_empty(Player), Player );
three_in_row_player( _Selected ) -> no_player.

three_in_row_player( true, Player ) -> Player;
three_in_row_player( false, _Player ) -> no_player.

turn( finished, Board ) -> result( Board );
turn( "X"=Player, Board ) ->
    N = computer_move( Player, Board ),
    io:fwrite( "Computer, ~p, selected ~p~n", [Player, N] ),
    New_board = [{N, Player} | lists:keydelete(N, 1, Board)],
    turn( player(is_finished(New_board), Player), New_board );
turn( "O"=Player, Board ) ->
    [turn_board_write_horisontal(X, Board) || X <- three_in_row_horisontal()], 
    Ns = [X || {X, Y} <- Board, is_empty(Y)],
    Prompt = lists:flatten( io_lib:format("Player, ~p, select one of ~p: ", [Player, Ns]) ),
    N = turn_next_move( Prompt, Ns ),
    New_board = [{N, Player} | lists:keydelete(N, 1, Board)], 
    turn( player(is_finished(New_board), Player), New_board ).

turn_board_write_horisontal( Selections, Board ) ->
	Tuples = [lists:keyfind(X, 1, Board) || X <- Selections],
	[io:fwrite( "~p ", [Y]) || {_X, Y} <- Tuples],
	io:fwrite( "~n" ).

turn_next_move( Prompt, Ns ) ->
	{ok,[N]} = io:fread( Prompt, "~d" ),
	turn_next_move_ok( lists:member(N, Ns), Prompt, Ns, N ).

turn_next_move_ok( true, _Prompt, _Ns, N ) -> N;
turn_next_move_ok( false, Prompt, Ns, _N ) -> turn_next_move( Prompt, Ns ).
Output:
96> tic_tac_toe:task().
"1" "2" "3" 
"4" "5" "6" 
"7" "8" "9" 
Player, "O", select one of [1,2,3,4,5,6,7,8,9]: 5
Computer, "X", selected 2
"1" "X" "3" 
"4" "O" "6" 
"7" "8" "9" 
Player, "O", select one of [1,3,4,6,7,8,9]: 1
Computer, "X", selected 9
"O" "X" "3" 
"4" "O" "6" 
"7" "8" "X" 
Player, "O", select one of [3,4,6,7,8]: 3
Computer, "X", selected 7
"O" "X" "O" 
"4" "O" "6" 
"X" "8" "X" 
Player, "O", select one of [4,6,8]: 8
Computer, "X", selected 6
"O" "X" "O" 
"4" "O" "X" 
"X" "O" "X" 
Player, "O", select one of [4]: 4
Result: draw.

ERRE

Taken from ERRE distribution disk: comments and messages are in Italian.

!--------------------------------------------
! TRIS.R : gioca a tris contro l'operatore
!--------------------------------------------

PROGRAM TRIS

DIM TRIS%[9],T1%[9],PIECES$[3]

!$SEGMENT=$B800

!$INCLUDE="PC.LIB"

PROCEDURE DELAY(COUNT%)
  FOR Z%=1 TO COUNT DO
  END FOR
END PROCEDURE

PROCEDURE SET_BOARD
!
! Disegna lo schema del gioco
!
  CLS
  BLOAD("TRIS.BLD",0)
!$KEY
END PROCEDURE

PROCEDURE PUT_PIECES
!
! Pone i pezzi sulla scacchiera
!
  Z%=0
  FOR ROW%=6 TO 12 STEP 3 DO     ! posizioni assolute sullo schermo
    FOR COL%=32 TO 48 STEP 8 DO
      LOCATE(ROW%+1,COL%+1)
      Z%=Z%+1
      PRINT(PIECES$[TRIS%[Z%]])
    END FOR
  END FOR
END PROCEDURE

PROCEDURE COMPUTE_MOVE(A%)
  CASE A% OF
    2-> C1%=C1%+1            END ->
    4-> C2%=C2%+1            END ->
    8-> S1%=TRUE  S2%=TRUE   END ->
    3-> N1%=N1%+1            END ->
    9-> N2%=N2%+1            END ->
   27-> S1%=FALSE S2%=FALSE  END ->
 END CASE
END PROCEDURE

PROCEDURE PREPAREMOVE(T1%[],I%->M%)
!
! Prepara la mossa del calcolatore
!
   T1%[I%]=2
   C1%=0
   C2%=0
   N1%=0
   N2%=0
   FOR K%=0 TO 2 DO
     COMPUTE_MOVE(T1%[3*K%+1]*T1%[3*K%+2]*T1%[3*K%+3])
     COMPUTE_MOVE(T1%[K%+1]*T1%[K%+4]*T1%[K%+7])
   END FOR
   COMPUTE_MOVE(T1%[1]*T1%[5]*T1%[9])
   COMPUTE_MOVE(T1%[3]*T1%[5]*T1%[7])
   M%=-63*N2%+31*C2%-15*N1%+7*C1%
END PROCEDURE

PROCEDURE COMPUTER_MOVE
!
! Coordina le mosse del calcolatore
!
  MAXSCORE%=-1000
  FOR I%=1 TO 9 DO
    IF TRIS%[I%]=1
      THEN
       PREPAREMOVE(TRIS%[],I%->MV%)
       EXIT IF S2% AND NOT S1%
       IF S1% AND S2%
         THEN
          TRIS%[I%]=2
          DIARY$=DIARY$+"c"+MID$(STR$(I%),2)+"*"
          PUT_PIECES
          EXIT
       END IF
       IF MV%=0
         THEN
          MOVE%=I%
          EXIT
       END IF
       IF MV%>MAXSCORE%
         THEN
          MOVE%=I%
          MAXSCORE%=MV%
       END IF
    END IF
  END FOR
  IF NOT S2%
    THEN
     TRIS%[MOVE%]=2
     DIARY$=DIARY$+"c"+MID$(STR$(MOVE%),2)+";"
     PUT_PIECES
     NMOVE%=NMOVE%-1
     S1%=(NMOVE%=0)
  END IF
END PROCEDURE

PROCEDURE PLAYER_MOVE
!
! Gioca l'avversario umano usando i tasti cursore per lo spostamento
!
  LOCATE(19,13)
  PRINT("Tocca a te ....                  ")
  REPEAT
    ROW%=7
    COL%=32
    LOCATE(ROW%+1,COL%+1)
    PRINT("Ü")
    REPEAT
      GET(B$)
      IF LEN(B$)=2 THEN
        CASE ASC(RIGHT$(B$,1)+CHR$(0)) OF
          77-> ! codice tastiera per CRSR =>
             LOCATE(ROW%+1,COL%+1)
             PRINT(" ")
             COL%=-(COL%+8)*(COL%<=40)-32*(COL%>40)
             LOCATE(ROW%+1,COL%+1)
             PRINT("Ü")
          END ->
          75-> ! codice tastiera per CRSR <=
             LOCATE(ROW%+1,COL%+1)
             PRINT(" ")
             COL%=-(COL%-8)*(COL%>=40)-48*(COL%<40)
             LOCATE(ROW%+1,COL%+1)
             PRINT("Ü")
          END ->
          80-> ! codice tastiera per CRSR DOWN
             LOCATE(ROW%+1,COL%+1)
             PRINT(" ")
             ROW%=-(ROW%+3)*(ROW%<=10)-7*(ROW%>10)
             LOCATE(ROW%+1,COL%+1)
             PRINT("Ü")
          END ->
          72-> ! codice tastiera per CRSR UP
             LOCATE(ROW%+1,COL%+1)
             PRINT(" ")
             ROW%=-(ROW%-3)*(ROW%>=10)-13*(ROW%<10)
             LOCATE(ROW%+1,COL%+1)
             PRINT("Ü")
          END ->
       END CASE
      END IF
     UNTIL B$=CHR$(13)
     MM%=ROW%+COL%/8-10 ! da coordinate schermo a coordinate scacchiera
   UNTIL TRIS%[MM%]=1
  TRIS%[MM%]=3
  LOCATE(ROW%+1,COL%+1)
  PRINT(" ")
  DIARY$=DIARY$+"p"+MID$(STR$(MM%),2)+";"
  PUT_PIECES
  NMOVE%=NMOVE%-1
  S1%=(NMOVE%=0)
  LOCATE(19,13)
  PRINT(STRING$(45," "))
END PROCEDURE

BEGIN
  DATA(" ","+","o")
  SET_BOARD
  REPEAT
    S1%=FALSE    S2%=FALSE   ! determinano lo stato della partita
    NMOVE%=9
    FOR Z%=1 TO 3 DO
       READ(PIECES$[Z%])
    END FOR
    FOR Z%=1 TO 9 DO
        TRIS%[Z%]=1
    END FOR
    LOCATE(19,13)
    PRINT("Giochi per primo ?")
    REPEAT
      GET(A$)
    UNTIL A$="S" OR A$="s" OR A$="N" OR A$="n"
    PUT_PIECES
    FOR INDICE%=1 TO 9 DO
      IF A$="s" OR A$="S"
        THEN
          PLAYER_MOVE
          EXIT IF S1% OR S2%
          COMPUTER_MOVE
          EXIT IF S1% OR S2%
        ELSE
          COMPUTER_MOVE
          EXIT IF S1% OR S2%
          PLAYER_MOVE
          EXIT IF S1% OR S2%
      END IF
   END FOR
   LOCATE(19,13)
   CASE TRUE OF
     (S1% AND NOT S2%)->
        PRINT("E' finita pari !!!     ")
     END ->
     (S2% AND NOT S1%)->
        PRINT("HAI VINTO !!!          ")
     END ->
     (S1% AND S2%)->
        PRINT("HO VINTO IO !!!        ")
     END ->
   END CASE
   DELAY(500)
   LOCATE(19,13)
   PRINT(DIARY$)
   DELAY(500)
   LOCATE(19,13)
   PRINT("Vuoi giocare ancora ?       ")
   REPEAT
     GET(A$)
   UNTIL A$="S" OR A$="s" OR A$="N" OR A$="n"
 UNTIL A$="N" OR A$="n"
END PROGRAM
Output:

A game example

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 ░░▒▒▓▓                                                                  ▓▓▒▒░░
 ░░▒▒▓▓ ┌───────────────┐   ╔═══════╤═══════╤═══════╗   ┌────────────┐   ▓▓▒▒░░
 ░░▒▒▓▓ │───── TRIS ────│   ║   +   │   o   │   +   ║   │Il calcola- │   ▓▓▒▒░░
 ░░▒▒▓▓ │               │   ║       │       │       ║   │tore non può│   ▓▓▒▒░░
 ░░▒▒▓▓ │Si gioca contro│   ╟───────┼───────┼───────╢   │perdere e   │   ▓▓▒▒░░
 ░░▒▒▓▓ │il calcolatore.│   ║   +   │   o   │   o   ║   │perciò il   │   ▓▓▒▒░░
 ░░▒▒▓▓ │Per muoversi   │   ║       │       │       ║   │giocatore   │   ▓▓▒▒░░
 ░░▒▒▓▓ │usare i tasti  │   ╟───────┼───────┼───────╢   │può al mas- │   ▓▓▒▒░░
 ░░▒▒▓▓ │cursore e ◄──┘ │   ║   o   │   +   │   o   ║   │simo pareg- │   ▓▓▒▒░░
 ░░▒▒▓▓ │per confermare.│   ║       │       │       ║   │giare.      │   ▓▓▒▒░░
 ░░▒▒▓▓ └───────────────┘   ╚═══════╧═══════╧═══════╝   └────────────┘   ▓▓▒▒░░
 ░░▒▒▓▓                                                                  ▓▓▒▒░░
 ░░▒▒▓▓                                                                  ▓▓▒▒░░
 ░░▒▒▓▓  ┌────────────────────────────────────────────────────────────┐  ▓▓▒▒░░
 ░░▒▒▓▓  │  Vuoi giocare ancora ?                                     │  ▓▓▒▒░░
 ░░▒▒▓▓  └────────────────────────────────────────────────────────────┘  ▓▓▒▒░░
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Euphoria

Works with: OpenEuphoria

No computer AI

include std/console.e
include std/text.e
include std/search.e
include std/sequence.e

sequence board 
sequence players = {"X","O"}

function DisplayBoard()
	for i = 1 to 3 do
		for j = 1 to 3 do
			printf(1,"%s",board[i][j])
			if j < 3 then
				printf(1,"%s","|")
			end if
		end for
		if i < 3 then
			puts(1,"\n-----\n")
		else
			puts(1,"\n\n")
		end if
	end for
	
	return 1
end function

function CheckWinner()
sequence temp = board
	for a = 1 to 2 do
		for i = 1 to 3 do
			if equal({"X","X","X"},temp[i]) then
				puts(1,"X wins\n\n")
				return 1
			elsif equal({"O","O","O"},temp[i]) then
				puts(1,"O wins\n\n")
				return 1
			end if
		end for
		temp = columnize(board)
	end for
	if equal({"X","X","X"},{board[1][1],board[2][2],board[3][3]}) or
	   equal({"X","X","X"},{board[1][3],board[2][2],board[3][1]}) then
		puts(1,"X wins\n")
		return 1
	elsif equal({"O","O","O"},{board[1][1],board[2][2],board[3][3]}) or
	   equal({"O","O","O"},{board[1][3],board[2][2],board[3][1]}) then
		puts(1,"O wins\n")
		return 1
	end if	
	
	if moves = 9 then
		puts(1,"Draw\n\n")
		return 1
	end if
	
	return 0
end function

integer turn, row, column, moves
sequence replay
while 1 do
	board = repeat(repeat(" ",3),3)
	DisplayBoard()
	turn = rand(2)
	moves = 0
	
	while 1 do
		while 1 do
			printf(1,"%s's turn\n",players[turn])
			row = prompt_number("Enter row: ",{})
			column = prompt_number("Enter column: ",{})
			if match(board[row][column]," ") then
				board[row][column] = players[turn]
				moves += 1
				exit
			else
				puts(1,"Space already taken - pick again\n")
			end if
		end while
		
		DisplayBoard()
		
		if CheckWinner() then
			exit
		end if
		
		if turn = 1 then
			turn = 2
		else
			turn = 1
		end if
	end while

	replay = lower(prompt_string("Play again (y/n)?\n\n"))
	
	if match(replay,"n") then
		exit
	end if

end while
Output:
 | |
-----
 | |
-----
 | |

O's turn
Enter row: 1
Enter column: 1
O| |
-----
 | |
-----
 | |

X's turn
Enter row: 3
Enter column: 3
O| |
-----
 | |
-----
 | |X

O's turn
Enter row: 3
Enter column: 1
O| |
-----
 | |
-----
O| |X

X's turn
Enter row: 2
Enter column: 1
O| |
-----
X| |
-----
O| |X

O's turn
Enter row: 2
Enter column: 2
O| |
-----
X|O|
-----
O| |X

X's turn
Enter row: 1
Enter column: 3
O| |X
-----
X|O|
-----
O| |X

O's turn
Enter row: 1
Enter column: 2
O|O|X
-----
X|O|
-----
O| |X

X's turn
Enter row: 3
Enter column: 2
O|O|X
-----
X|O|
-----
O|X|X

O's turn
Enter row: 2
Enter column: 3
O|O|X
-----
X|O|O
-----
O|X|X

Draw

Play again (y/n)?

F#

A purely-functional solution with a naive (but perfect) computer player implementation. The first move is played randomly by the computer.

type Brick =
 | Empty
 | Computer
 | User

let brickToString = function
 | Empty -> ' '
 | Computer -> 'X'
 | User -> 'O'

// y -> x -> Brick
type Board = Map<int, Map<int, Brick> >

let emptyBoard =
  let emptyRow = Map.ofList [0,Empty; 1,Empty; 2,Empty]
  Map.ofList [0,emptyRow; 1,emptyRow; 2,emptyRow]

let get (b:Board) (x,y) = b.[y].[x]

let set player (b:Board) (x,y) : Board =
  let row = b.[y].Add(x, player)
  b.Add(y, row)

let winningPositions = 
  [for x in [0..2] -> x,x] // first diagonal
  ::[for x in [0..2] -> 2-x,x] // second diagonal
  ::[for y in [0..2] do
     yield! [[for x in [0..2]->(y,x)]; // columns
             [for x in [0..2] -> (x,y)]]] // rows
  
let hasWon player board = 
  List.exists
    (fun ps -> List.forall (fun pos -> get board pos = player) ps)
    winningPositions

let freeSpace board =
  [for x in 0..2 do
     for y in 0..2 do
       if get board (x,y) = Empty then yield x,y]

type Evaluation =
 | Win
 | Draw
 | Lose

let rec evaluate board move =
  let b2 = set Computer board move
  if hasWon Computer b2 then Win
  else
    match freeSpace b2 with
    | [] -> Draw
    | userChoices -> 
       let b3s = List.map (set User b2) userChoices
       if List.exists (hasWon User) b3s then Lose
       elif List.exists (fun b3 -> bestOutcome b3 = Lose) b3s
       then Lose
       elif List.exists (fun b3 -> bestOutcome b3 = Draw) b3s
       then Draw
       else Win
        
and findBestChoice b =
  match freeSpace b with
  | [] -> ((-1,-1), Draw)
  | choices -> 
    match List.tryFind (fun c -> evaluate b c = Win) choices with
    | Some c -> (c, Win)
    | None -> match List.tryFind (fun c -> evaluate b c = Draw) choices with
              | Some c -> (c, Draw)
              | None -> (List.head choices, Lose)

and bestOutcome b = snd (findBestChoice b)

let bestChoice b = fst (findBestChoice b)

let computerPlay b = set Computer b (bestChoice b)
       
let printBoard b =
  printfn "   | A | B | C |"
  printfn "---+---+---+---+"
  for y in 0..2 do
   printfn " %d | %c | %c | %c |"
    (3-y)
    (get b (0,y) |> brickToString)
    (get b (1,y) |> brickToString)
    (get b (2,y) |> brickToString)
   printfn "---+---+---+---+"

let rec userPlay b =
  printfn "Which field do you play? (format: a1)"
  let input = System.Console.ReadLine()
  if input.Length <> 2
     || input.[0] < 'a' || input.[0] > 'c'
     || input.[1] < '1' || input.[1] > '3' then
     printfn "illegal input"
     userPlay b
  else
     let x = int(input.[0]) - int('a')
     let y = 2 - int(input.[1]) + int('1')
     if get b (x,y) <> Empty then
       printfn "Field is not free."
       userPlay b
     else
       set User b (x,y)

let rec gameLoop b player =
  if freeSpace b = [] then
    printfn "Game over. Draw."
  elif player = Computer then
    printfn "Computer plays..."
    let b2 = computerPlay b
    printBoard b2
    if hasWon Computer b2 then
      printfn "Game over. I have won."
    else
      gameLoop b2 User
  elif player = User then
    let b2 = userPlay b
    printBoard b2
    if hasWon User b2 then
      printfn "Game over. You have won."
    else
      gameLoop b2 Computer

// randomly choose an element of a list
let choose =
  let rnd = new System.Random()
  fun (xs:_ list) -> xs.[rnd.Next(xs.Length)]

// play first brick randomly
printfn "Computer starts."
let b = set Computer emptyBoard (choose (freeSpace emptyBoard))
printBoard b
gameLoop b User

Example game:

Computer starts.
   | A | B | C |
---+---+---+---+
 3 |   |   | X |
---+---+---+---+
 2 |   |   |   |
---+---+---+---+
 1 |   |   |   |
---+---+---+---+
Which field do you play? (format: a1)
a1
   | A | B | C |
---+---+---+---+
 3 |   |   | X |
---+---+---+---+
 2 |   |   |   |
---+---+---+---+
 1 | O |   |   |
---+---+---+---+
Computer plays...
   | A | B | C |
---+---+---+---+
 3 | X |   | X |
---+---+---+---+
 2 |   |   |   |
---+---+---+---+
 1 | O |   |   |
---+---+---+---+
Which field do you play? (format: a1)
b3
   | A | B | C |
---+---+---+---+
 3 | X | O | X |
---+---+---+---+
 2 |   |   |   |
---+---+---+---+
 1 | O |   |   |
---+---+---+---+
Computer plays...
   | A | B | C |
---+---+---+---+
 3 | X | O | X |
---+---+---+---+
 2 |   |   |   |
---+---+---+---+
 1 | O |   | X |
---+---+---+---+
Which field do you play? (format: a1)
c2
   | A | B | C |
---+---+---+---+
 3 | X | O | X |
---+---+---+---+
 2 |   |   | O |
---+---+---+---+
 1 | O |   | X |
---+---+---+---+
Computer plays...
   | A | B | C |
---+---+---+---+
 3 | X | O | X |
---+---+---+---+
 2 |   | X | O |
---+---+---+---+
 1 | O |   | X |
---+---+---+---+
Game over. I have won.


Forth

Works with: gforth version 0.7.3

Game between two humans.

create board 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ,

\ board: 0=empty, 1=player X, 2=player O
: player. ( player -- ) C"  XO" 1+ + @ emit ;
: spot ( n -- addr ) cells board + ;
: clean-board ( -- ) 9 0 do 0 i spot ! loop ;
  
: show-board
  CR ." +---+---+---+  +---+---+---+" CR
  3 0 do
    ." | "
    3 0 do
      i j 3 * + spot @ player. ."  | "
    loop
    ."  | "
    3 0 do
      i j 3 * + . ." | "
    loop
    CR ." +---+---+---+  +---+---+---+" CR
  loop ;

: spots-equal ( n1 n2 n3 -- f )
  over   spot @ swap spot @   = >r   spot @ swap spot @   =   r>   and ;
: spots-win ( n1 n2 n3 -- f )
  dup >r spots-equal r> spot @ 0<> and ;

: winner-check ( -- player )
  0 1 2 spots-win if 0 spot @ exit then
  3 4 5 spots-win if 3 spot @ exit then
  6 7 8 spots-win if 6 spot @ exit then
  0 3 6 spots-win if 0 spot @ exit then
  1 4 7 spots-win if 1 spot @ exit then
  2 5 8 spots-win if 2 spot @ exit then
  0 4 8 spots-win if 0 spot @ exit then
  2 4 6 spots-win if 2 spot @ exit then
  0 ;

: player-move ( player -- )
  begin
    key dup emit [char] 0 - dup
    spot @ 0= if spot ! exit else drop then
  again ;

: game
  clean-board show-board
  9 0 do
    i 2 mod 1+ dup ." Player " player. ." : "
    player-move show-board
    winner-check dup 0<> if player. ."  wins !" unloop exit else drop then
  loop
  ." Draw!" ;

game
Output:
+---+---+---+  +---+---+---+
|   |   |   |  | 0 | 1 | 2 | 
+---+---+---+  +---+---+---+
|   |   |   |  | 3 | 4 | 5 | 
+---+---+---+  +---+---+---+
|   |   |   |  | 6 | 7 | 8 | 
+---+---+---+  +---+---+---+
Player X: 0
+---+---+---+  +---+---+---+
| X |   |   |  | 0 | 1 | 2 | 
+---+---+---+  +---+---+---+
|   |   |   |  | 3 | 4 | 5 | 
+---+---+---+  +---+---+---+
|   |   |   |  | 6 | 7 | 8 | 
+---+---+---+  +---+---+---+
Player O: 3
+---+---+---+  +---+---+---+
| X |   |   |  | 0 | 1 | 2 | 
+---+---+---+  +---+---+---+
| O |   |   |  | 3 | 4 | 5 | 
+---+---+---+  +---+---+---+
|   |   |   |  | 6 | 7 | 8 | 
+---+---+---+  +---+---+---+
Player X: 1
+---+---+---+  +---+---+---+
| X | X |   |  | 0 | 1 | 2 | 
+---+---+---+  +---+---+---+
| O |   |   |  | 3 | 4 | 5 | 
+---+---+---+  +---+---+---+
|   |   |   |  | 6 | 7 | 8 | 
+---+---+---+  +---+---+---+
Player O: 4
+---+---+---+  +---+---+---+
| X | X |   |  | 0 | 1 | 2 | 
+---+---+---+  +---+---+---+
| O | O |   |  | 3 | 4 | 5 | 
+---+---+---+  +---+---+---+
|   |   |   |  | 6 | 7 | 8 | 
+---+---+---+  +---+---+---+
Player X: 2
+---+---+---+  +---+---+---+
| X | X | X |  | 0 | 1 | 2 | 
+---+---+---+  +---+---+---+
| O | O |   |  | 3 | 4 | 5 | 
+---+---+---+  +---+---+---+
|   |   |   |  | 6 | 7 | 8 | 
+---+---+---+  +---+---+---+
X wins ! ok



Fortran

Objective: write program in less than 100 lines, not using semicolons. Computer never loses, but plays as random as possible. Player gets first move of first game. Afterwards, first move alternates between computer and player.

! This is a fortran95 implementation of the game of tic-tac-toe.
! - Objective was to use less than 100 lines.
! - No attention has been devoted to efficiency.
! - Indentation by findent: https://sourceforge.net/projects/findent/
! - This is free software, use as you like at own risk.
! - Compile: gfortran -o tictactoe tictactoe.f90
! - Run: ./tictactoe
! Comments to: wvermin at gmail dot com
module tic
   implicit none
   integer :: b(9)
contains
   logical function iswin(p)
      integer,intent(in) :: p
      iswin = &
         all(b([1,2,3])==p).or.all(b([4,5,6])==p).or.all(b([7,8,9])==p).or.&
         all(b([1,4,7])==p).or.all(b([2,5,8])==p).or.all(b([3,6,9])==p).or.&
         all(b([1,5,9])==p).or.all(b([3,5,7])==p)
   end function iswin
   subroutine printb(mes)
      character(len=*) :: mes
      integer          :: i,j
      character        :: s(0:2) = ['.','X','O']
      print "(3a3,'   ',3i3)",(s(b(3*i+1:3*i+3)),(j,j=3*i+1,3*i+3),i=0,2)
      if(mes /= ' ') print "(/,a)",mes
   end subroutine printb
   integer recursive function minmax(player,bestm) result(bestv)
      integer :: player,bestm,move,v,bm,win=1000,inf=100000
      real    :: x
      if (all(b .ne. 0)) then
         bestv = 0
      else
         bestv = -inf
         do move=1,9
            if (b(move) == 0) then
               b(move) = player
               if (iswin(player)) then
                  v = win
               else
                  call random_number(x)
                  v = -minmax(3-player,bm) - int(10*x)
               endif
               if (v > bestv) then
                  bestv = v
                  bestm = move
               endif
               b(move) = 0
               if (v == win) exit
            endif
         enddo
      endif
   end function minmax
end module tic
program tictactoe
   ! computer: player=1, user: player=2
   use tic
   implicit none 
   integer :: move,ios,v,bestmove,ply,player=2,k,values(8)
   integer,allocatable :: seed(:)
   call date_and_time(values=values)
   call random_seed(size=k)
   allocate(seed(k))
   seed = values(8)+1000*values(7)+60*1000*values(6)+60*60*1000*values(5)
   call random_seed(put=seed)
   mainloop: do
      b = 0
      call printb('You have O, I have X. You enter 0: game ends.')
      plyloop: do ply=0,4
         if (player == 2 .or. ply >0 ) then  ! user move
            write(*,"(/,a)",advance='no'),'Your move? (0..9) '
            getloop: do
               readloop: do
                  read (*,*,iostat=ios),move
                  if (ios == 0 .and. move  >= 0 .and. move <= 9) exit readloop
                  write(*,"(a)",advance='no'),'huh? Try again (0..9): '
               enddo readloop
               if (  move  == 0) exit mainloop
               if (b(move) == 0) exit getloop
               write(*,"(a)",advance='no'),'Already occupied, again (0..9): '
            enddo getloop
            b(move) = 2
            if(iswin(2)) then   ! this should not happen
               call printb('***** You win *****')
               exit plyloop
            endif
         endif
         v = minmax(1,bestmove)   ! computer move
         b(bestmove) = 1
         if(iswin(1)) then
            call printb('***** I win *****')
            exit plyloop
         endif
         write(*,"(/,a,i3)"), 'My move: ',bestmove
         call printb(' ')
      enddo plyloop
      if(ply == 5) write(*,"('***** Draw *****',/)")
      player = 3-player
   enddo mainloop
end program

Go

Intermediate, like Python's "Better skilled player." Computer wins and blocks where it can, but otherwise plays randomly. Plays multiple games and keeps score. Player gets first move of first game. Afterwards, loser gets to go first, or after cat games, first move alternates.

package main

import (
    "bufio"
    "fmt"
    "math/rand"
    "os"
    "strings"
)

var b []byte

func printBoard() {
    fmt.Printf("%s\n%s\n%s\n", b[0:3], b[3:6], b[6:9])
}

var pScore, cScore int
var pMark, cMark byte = 'X', 'O'
var in = bufio.NewReader(os.Stdin)

func main() {
    b = make([]byte, 9)
    fmt.Println("Play by entering a digit.")
    for {
        // start of game
        for i := range b {
            b[i] = '1' + byte(i)
        }
        computerStart := cMark == 'X'
        if computerStart {
            fmt.Println("I go first, playing X's")
        } else {
            fmt.Println("You go first, playing X's")
        }
    TakeTurns:
        for {
            if !computerStart {
                if !playerTurn() {
                    return
                }
                if gameOver() {
                    break TakeTurns
                }

            }
            computerStart = false
            computerTurn()
            if gameOver() {
                break TakeTurns
            }
        }
        fmt.Println("Score: you", pScore, "me", cScore)
        fmt.Println("\nLet's play again.")
    }
}

func playerTurn() bool {
    var pm string
    var err error
    for i := 0; i < 3; i++ { // retry loop
        printBoard()
        fmt.Printf("%c's move? ", pMark)
        if pm, err = in.ReadString('\n'); err != nil {
            fmt.Println(err)
            return false
        }
        pm = strings.TrimSpace(pm)
        if pm >= "1" && pm <= "9" && b[pm[0]-'1'] == pm[0] {
            x := pm[0] - '1'
            b[x] = pMark
            return true
        }
    }
    fmt.Println("You're not playing right.")
    return false
}

var choices = make([]int, 9)

func computerTurn() {
    printBoard()
    var x int
    defer func() {
        fmt.Println("My move:", x+1)
        b[x] = cMark
    }()
    // look for two in a row
    block := -1
    for _, l := range lines {
        var mine, yours int
        x = -1
        for _, sq := range l {
            switch b[sq] {
            case cMark:
                mine++
            case pMark:
                yours++
            default:
                x = sq
            }
        }
        if mine == 2 && x >= 0 {
            return // strategy 1: make winning move
        }
        if yours == 2 && x >= 0 {
            block = x
        } 
    }
    if block >= 0 {
        x = block // strategy 2: make blocking move
        return
    }
    // default strategy: random move
    choices = choices[:0]
    for i, sq := range b { 
        if sq == '1'+byte(i) {
            choices = append(choices, i)
        }
    }
    x = choices[rand.Intn(len(choices))]
}   
    
func gameOver() bool {
    // check for win
    for _, l := range lines {
        if b[l[0]] == b[l[1]] && b[l[1]] == b[l[2]] {
            printBoard()
            if b[l[0]] == cMark {
                fmt.Println("I win!")
                cScore++
                pMark, cMark = 'X', 'O'
            } else {
                fmt.Println("You win!")
                pScore++
                pMark, cMark = 'O', 'X'
            }
            return true 
        } 
    }
    // check for empty squares
    for i, sq := range b {
        if sq == '1'+byte(i) {
            return false
        }
    }
    fmt.Println("Cat game.")
    pMark, cMark = cMark, pMark
    return true
}

var lines = [][]int{
    {0, 1, 2}, // rows
    {3, 4, 5},
    {6, 7, 8},
    {0, 3, 6}, // columns
    {1, 4, 7},
    {2, 5, 8},
    {0, 4, 8}, // diagonals
    {2, 4, 6},
}

Groovy

Simplified version of Tic Tac Toe for player vs. player (no AI computer-controlled option).

class Main {

	def input = new Scanner(System.in)
	
	static main(args) {
		Main main = new Main();
		main.play();
	}

	public void play() {

		TicTackToe game = new TicTackToe();
		game.init()
		def gameOver = false		
		def player = game.player1
		
		println "Players take turns marking a square. Only squares \n"+
				"not already marked can be picked. Once a player has \n"+
    			"marked three squares in a row, column or diagonal, they win! If all squares \n"+
    			"are marked and no three squares are the same, a tied game is declared.\n"+
				"Player 1 is O and Player 2 is X \n"+
    			"Have Fun! \n\n"
		println "${game.drawBoard()}"

		while (!gameOver && game.plays < 9) {
			
			player = game.currentPlayer == 1 ? game.player1 :game.player2
			def validPick = false;
			while (!validPick) {
				
				def square
				println "Next $player, enter move by selecting square's number :"	
				try {
					square = input.nextLine();
				} catch (Exception ex) { }					
				 			
				if (square.length() == 1 && Character.isDigit(square.toCharArray()[0])) {	validPick = game.placeMarker(square)	}
				if (!validPick) {	println "Select another Square"	}
				
			}
			
			(game.checkWinner(player))?	gameOver = true	: game.switchPlayers()			
			println(game.drawBoard());	
				
		}		
		println "Game Over, " + ((gameOver == true)? "$player Wins" : "Draw")
	}

}

public class TicTackToe {
	
    def board = new Object[3][3]
	def final player1 = "player 1"
	def final player2 = "player 2"
	def final marker1 = 'X'
	def final marker2 = 'O'
	
    int currentPlayer
	int plays
    
	public TicTacToe(){
		
	}

 
    def init() {
        int counter = 0;
       (0..2).each { row ->
           (0..2).each { col ->
                board[row][col] = (++counter).toString();
            }
        }
	   plays = 0
	   currentPlayer =1
    }

    def switchPlayers() {
        currentPlayer = (currentPlayer == 1) ? 2:1
        plays++
    }

    def placeMarker(play) {
		def result = false
        (0..2).each { row ->
            (0..2).each { col ->
                if (board[row][col].toString()==play.toString()){
                    board[row][col] = (currentPlayer == 1) ? marker2 : marker1;
                    result =  true;
                }
            }
        }
        return result;
    }

    def checkWinner(player) {
    	char current = (player == player1)? marker2:  marker1
        //Checking 
        return checkRows(current) || checkColumns(current) ||checkDiagonals(current);
    }
    
    def checkRows(char current){
		(0..2).any{ line ->
			  board[line].every { it == current}
		}
    }
    
    
    def checkColumns(char current){				
		(0..2).any{i ->
			(0..2).every{j ->
				 board[j][i]==current }		
		}
    }

    def checkDiagonals(char current){
		def rightDiag = [board[0][0],board[1][1],board[2][2]]
		def leftDiag =  [board[0][2],board[1][1],board[2][0]]
		return rightDiag.every{it == current} || leftDiag.every{it == current}
    }
    

    def drawBoard() {
        StringBuilder builder = new StringBuilder("Game board: \n");
        (0..2).each { row->
            (0..2).each {col ->
                builder.append("[" + board[row][col] + "]");
            }
            builder.append("\n");
        }
        builder.append("\n");
        return builder.toString();
    }
}

Haskell

Computer player has three strategies: 1. Try to block the opponent first, 2. Try to guess a good position for the next move, 3. Place a piece randomly. There are lots of comments throughout the code.

module Main where

import System.Random
import Data.List (intercalate, find, minimumBy)
import System.Environment (getArgs)
import Data.Char (digitToInt)
import Data.Maybe (listToMaybe, mapMaybe)
import Control.Monad (guard)
import Data.Ord (comparing)

-- check if there is a horizontal, vertical or diagonal line of
-- X or O
tictactoe :: String -> Bool
tictactoe a = tictactoeFor 'X' a /= tictactoeFor 'O' a

-- check if there is a horizontal, vertical or diagonal line
-- for the given player "n"
tictactoeFor :: Char -> String -> Bool
tictactoeFor n [a,b,c,d,e,f,g,h,i] =
    [n,n,n] `elem` [[a,b,c],[d,e,f],[g,h,i],[a,d,g],
                    [b,e,h],[c,f,i],[a,e,i],[c,e,g]]

-- empty game board
start :: String
start = "         "

-- check if there is an X or an O at the given position
isPossible :: Int -> String -> Bool
isPossible n game = (game !! n) `notElem` "XO"

-- try to place an X or an O at a given position.
-- "Right" + modified board means success, "Left" + unmodified board
-- means failure
place :: Int -> Char -> String -> Either String String
place i c game =
    if isPossible i game
    then Right $ take i game ++ [c] ++ drop (i + 1) game
    else Left game

-- COMPUTER AI
-- get the number of movements, starting from a given non-empty board
-- and a position for the next movement, until the specified player
-- wins or no movement is possible
-- the positions are chosen sequentially, so there's not much
-- intelligence here anyway
developGame :: Bool -> Int -> Int -> Char -> String -> (Int, Char, String)
developGame iterateMore moves i player game
    | i > 8 = 
        -- if i arrives to the last position, iterate again from 0
        -- but do it only once
        if iterateMore
        then developGame False moves 0 player game
        -- draw game (after one iteration, still no winning moves)
        else (moves, player, game)
        -- draw game (game board full) or a win for the player
    | moves == 9 || tictactoeFor player game = (moves, player, game)
        -- make a move, if possible, and continue playing
    | otherwise = case place i otherPlayer game of
        -- position i is not empty. try with the next position
        Left _ -> developGame iterateMore moves (i + 1)
                    otherPlayer game
        -- position i was empty, so it was a valid move.
        -- change the player and make a new move, starting at pos 0
        Right newGame -> developGame iterateMore (moves + 1) 0
                    otherPlayer newGame
        where
            otherPlayer = changePlayer player

-- COMPUTER AI
-- starting from a given non-empty board, try to guess which position
-- could lead the player to the fastest victory.
bestMoveFor :: Char -> String -> Int
bestMoveFor player game = bestMove
    where
        -- drive the game to its end for each starting position
        continuations = [ (x, developGame True 0 x player game) |
            x <- [0..8] ]
        -- compare the number of moves of the game and take the
        -- shortest one
        move (_, (m, _, _)) = m
        (bestMove, _) = minimumBy (comparing move) continuations

-- canBlock checks if the opponent has two pieces in a row and the
-- other cell in the row is empty, and places the player's piece there,
-- blocking the opponent
canBlock :: Char -> String -> Maybe Int
canBlock p [a,b,c,d,e,f,g,h,i] =
    listToMaybe $ mapMaybe blockable [[a,b,c],[d,e,f],[g,h,i],[a,d,g],
                                      [b,e,h],[c,f,i],[a,e,i],[c,e,g]]
    where
        blockable xs = do          
          guard $ length (filter (== otherPlayer) xs) == 2
          x <- find (`elem` "123456789") xs
          return $ digitToInt x
        otherPlayer = changePlayer p

-- format a game board for on-screen printing
showGame :: String -> String
showGame [a,b,c,d,e,f,g,h,i] =
    topBottom ++
    "|    | 1 | 2 | 3 |\n" ++
    topBottom ++
    row "0" [[a],[b],[c]] ++
    row "3" [[d],[e],[f]] ++
    row "6" [[g],[h],[i]]
    where
        topBottom = "+----+---+---+---+\n"
        row n x = "| " ++ n ++ "+ | " ++
            intercalate " | " x ++ " |\n" ++ topBottom

-- ask the user to press a numeric key and convert it to an int
enterNumber :: IO Int
enterNumber = do
    c <- getChar
    if c `elem` "123456789"
    then do
        putStrLn ""
        return $ digitToInt c
    else do
        putStrLn "\nPlease enter a digit!"
        enterNumber

-- a human player's turn: get the number of pieces put on the board,
-- the next piece to be put (X or O) and a game board, and return
-- a new game state, checking if the piece can be placed on the board.
-- if it can't, make the user try again.
turn :: (Int, Char, String) -> IO (Int, Char, String)
turn (count, player, game) = do
    putStr $ "Please tell me where you want to put an " ++
        [player] ++ ": "
    pos <- enterNumber
    case place (pos - 1) player game of
        Left oldGame -> do
            putStrLn "That place is already taken!\n"
            turn (count, player, oldGame)
        Right newGame ->
            return (count + 1, changePlayer player, newGame)

-- alternate between X and O players
changePlayer :: Char -> Char
changePlayer 'O' = 'X'
changePlayer 'X' = 'O'

-- COMPUTER AI
-- make an automatic turn, placing an X or an O game board.
-- the first movement is always random.
-- first, the computer looks for two pieces of his opponent in a row
-- and tries to block.
-- otherwise, it tries to guess the best position for the next movement.
-- as a last resort, it places a piece randomly.
autoTurn :: Bool -> (Int, Char, String) -> IO (Int, Char, String)
autoTurn forceRandom (count, player, game) = do
    -- try a random position 'cause everything else failed
    -- count == 0 overrides the value of forceRandom
    i <- if count == 0 || forceRandom
            then randomRIO (0,8)
            else return $
                case canBlock player game of
                    -- opponent can't be blocked. try to guess
                    -- the best movement
                    Nothing -> bestMoveFor player game
                    -- opponent can be blocked, so just do it!
                    Just blockPos -> blockPos
    -- if trying to place a piece at a calculated position doesn't work,
    -- just try again with a random value
    case place i player game of
        Left oldGame -> autoTurn True (count, player, oldGame)
        Right newGame -> do
            putStrLn $ "It's player " ++ [player] ++ "'s turn."
            return (count + 1, changePlayer player, newGame)

-- play a game until someone wins or the board becomes full.
-- depending on the value of the variable "auto", ask the user(s) to
-- put some pieces on the board or do it automatically
play :: Int -> (Int, Char, String) -> IO ()
play auto cpg@(_, player, game) = do
    newcpg@(newCount, newPlayer, newGame) <- case auto of
        -- if both players are human, always ask them
        0 -> turn cpg
        -- if both players are computer, always play auto
        1 -> autoTurn False cpg
        -- X is computer, O is human
        2 -> if player == 'X' then autoTurn False cpg else turn cpg
        -- X is human, O is computer
        3 -> if player == 'O' then autoTurn False cpg else turn cpg
    putStrLn $ "\n" ++ showGame newGame
    if tictactoe newGame
    then putStrLn $ "Player " ++ [changePlayer newPlayer] ++ " wins!\n"
    else
        if newCount == 9
        then putStrLn "Draw!\n"
        else play auto newcpg

-- main program: greet the user, ask for a game type, ask for the
-- player that'll start the game, and play the game beginning with an
-- empty board
main :: IO ()
main = do
    a <- getArgs
    if null a
    then usage
    else do
        let option = head a
        if option `elem` ["0","1","2","3"]
        then do
            putStrLn $ "\n" ++ showGame start
            let m = read option :: Int
            play m (0, 'X', start)
        else usage

usage :: IO ()
usage = do
    putStrLn "TIC-TAC-TOE GAME\n================\n"
    putStrLn "How do you want to play?"
    putStrLn "Run the program with one of the following options."
    putStrLn "0 : both players are human"
    putStrLn "1 : both players are computer"
    putStrLn "2 : player X is computer and player O is human"
    putStrLn "3 : player X is human and player O is computer"
    putStrLn "Player X always begins."
Output:

Player X is computer, O is human.

+----+---+---+---+
|    | 1 | 2 | 3 |
+----+---+---+---+
| 0+ |   |   |   |
+----+---+---+---+
| 3+ |   |   |   |
+----+---+---+---+
| 6+ |   |   |   |
+----+---+---+---+

It's player X's turn.

+----+---+---+---+
|    | 1 | 2 | 3 |
+----+---+---+---+
| 0+ |   |   |   |
+----+---+---+---+
| 3+ |   | X |   |
+----+---+---+---+
| 6+ |   |   |   |
+----+---+---+---+

Please tell me where you want to put an O: 1

+----+---+---+---+
|    | 1 | 2 | 3 |
+----+---+---+---+
| 0+ | O |   |   |
+----+---+---+---+
| 3+ |   | X |   |
+----+---+---+---+
| 6+ |   |   |   |
+----+---+---+---+

It's player X's turn.

+----+---+---+---+
|    | 1 | 2 | 3 |
+----+---+---+---+
| 0+ | O |   | X |
+----+---+---+---+
| 3+ |   | X |   |
+----+---+---+---+
| 6+ |   |   |   |
+----+---+---+---+

Please tell me where you want to put an O: 7

+----+---+---+---+
|    | 1 | 2 | 3 |
+----+---+---+---+
| 0+ | O |   | X |
+----+---+---+---+
| 3+ |   | X |   |
+----+---+---+---+
| 6+ | O |   |   |
+----+---+---+---+

It's player X's turn.

+----+---+---+---+
|    | 1 | 2 | 3 |
+----+---+---+---+
| 0+ | O |   | X |
+----+---+---+---+
| 3+ | X | X |   |
+----+---+---+---+
| 6+ | O |   |   |
+----+---+---+---+

Please tell me where you want to put an O: 6

+----+---+---+---+
|    | 1 | 2 | 3 |
+----+---+---+---+
| 0+ | O |   | X |
+----+---+---+---+
| 3+ | X | X | O |
+----+---+---+---+
| 6+ | O |   |   |
+----+---+---+---+

It's player X's turn.

+----+---+---+---+
|    | 1 | 2 | 3 |
+----+---+---+---+
| 0+ | O |   | X |
+----+---+---+---+
| 3+ | X | X | O |
+----+---+---+---+
| 6+ | O | X |   |
+----+---+---+---+

Please tell me where you want to put an O: 2

+----+---+---+---+
|    | 1 | 2 | 3 |
+----+---+---+---+
| 0+ | O | O | X |
+----+---+---+---+
| 3+ | X | X | O |
+----+---+---+---+
| 6+ | O | X |   |
+----+---+---+---+

It's player X's turn.

+----+---+---+---+
|    | 1 | 2 | 3 |
+----+---+---+---+
| 0+ | O | O | X |
+----+---+---+---+
| 3+ | X | X | O |
+----+---+---+---+
| 6+ | O | X | X |
+----+---+---+---+

Draw!

Icon and Unicon

The following works in both Icon and Unicon. The computer plays randomly against a human player, with legal moves enforced and wins/draws notified.

# Play TicTacToe

$define E " " # empty square
$define X "X" # X piece
$define O "O" # O piece

# -- define a board 
record Board(a, b, c, d, e, f, g, h, i)

procedure display_board (board, player)
  write ("\n===============")
  write (board.a || " | " || board.b || " | " || board.c)
  write ("---------")
  write (board.d || " | " || board.e || " | " || board.f)
  write ("---------")
  write (board.g || " | " || board.h || " | " || board.i)
end

# return a set of valid moves (empty positions) in given board
procedure empty_fields (board)
  fields := set()
  every i := !fieldnames(board) do 
    if (board[i] == E) then insert (fields, i)
  return fields
end

procedure game_start ()
  return Board (E, E, E, E, E, E, E, E, E)
end

procedure game_is_drawn (board)
  return *empty_fields(board) = 0
end

procedure game_won_by (board, player)
  return (board.a == board.b == board.c == player) |
         (board.d == board.e == board.f == player) |
         (board.g == board.h == board.i == player) |
         (board.a == board.d == board.g == player) | 
         (board.b == board.e == board.h == player) |
         (board.c == board.f == board.i == player) |
         (board.a == board.e == board.i == player) |
         (board.g == board.e == board.c == player)
end

procedure game_over (board)
  return game_is_drawn (board) | game_won_by (board, O) | game_won_by (board, X)
end

# -- players make their move on the board
#    assume there is at least one empty square

procedure human_move (board, player)
  choice := "z"
  options := empty_fields (board)
  # keep prompting until player selects a valid square
  until member (options, choice) do {
    writes ("Choose one of: ")
    every writes (!options || " ")
    writes ("\n> ") 
    choice := read ()
  }
  board[choice] := player
end

# pick and make a move at random from empty positions
procedure random_move (board, player)
  board[?empty_fields(board)] := player
end

# -- manage the game play
procedure play_game ()
  # hold procedures for players' move in variables
  player_O := random_move
  player_X := human_move

  # randomly determine if human or computer moves first
  if (?2 = 0) 
    then {
      write ("Human plays first as O")
      player_O := human_move
      player_X := random_move
    }
    else write ("Computer plays first, human is X")

  # set up the game to start
  board := game_start ()
  player := O
  display_board (board, player)
  # loop until the game is over, getting each player to move in turn
  until game_over (board) do { 
    write (player || " to play next")
    # based on player, prompt for the next move
    if (player == O)
      then (player_O (board, player))
      else (player_X (board, player))
    # change player to move
    player := if (player == O) then X else O
    display_board (board, player)
  }
  # finish by writing out result
  if game_won_by (board, O) 
    then write ("O won") 
    else if game_won_by (board, X) 
      then write ("X won")
      else write ("draw") # neither player won, so must be a draw
end

# -- get things started
procedure main ()
  play_game ()
end

J

To subsequent j poster: replacing this entry is fine by me.

Note 'ttt adjudicates or plays'

   use:  markers ttt characters

   characters represent the cell names.

   markers is a length 3 character vector of the
   characters to use for first and second player
   followed by the opponent's mark.
   'XOX' means X plays 1st, O is the other mark,
   and the first strategy plays 1st.
   'XOO' means X plays 1st, O is the other mark,
   and the second strategy moves first.

   The game  is set  up for  the computer as the
   first strategy (random), and human as second.

   A standard use:
      'XOX'ttt'abcdefghijkl'

   Example game reformatted w/ emacs artist-mode
   to fit your display:

      '#-#'ttt'wersdfxcv'
   w│e│r                     w│e│r        ....    -│e│r           .    -│e│#
   ─┼─┼─                 .   ─┼─┼─       ..       ─┼─┼─         ..     ─┼─┼─
   s│d│f                 .   s│#│f      ..        s│#│f        ..      -│#│f
   ─┼─┼─                ..   ─┼─┼─      .         ─┼─┼─      ...       ─┼─┼─
   x│c│v               ..    -│c│v      .         -│c│#     ..         -│c│#
   d                  ..     v         ..         r         .          VICTORY
   w│e│r             ..      w│e│r     ..         -│e│#     .
   ─┼─┼─           ...       ─┼─┼─     ..         ─┼─┼─    .
   s│#│f         ...         s│#│f     ..         s│#│f    .
   ─┼─┼─        ..           ─┼─┼─   ...          ─┼─┼─  ...
   x│c│v                     -│c│#                -│c│#
   -->cell for -?            -->cell for -?       -->cell for -?
   x                         w                    s
)

while=: conjunction def 'u ^: v ^:_' NB. j assumes while is a verb and needs to know while is a conjunction.

ttt=: outcome@:((display@:move) while undecided)@:display@:prepare

blindfolded_variant=: outcome@:display@:(move while undecided)@:display@:prepare

outcome=: {&(>;:'kitty VICTORY')@:won   NB. (outcome does not pass along the state)
move=: post locate
undecided=: won nor full
prepare=: , board@:]                    NB. form the state vector

Note 'locate'
  is a monadic verb.  y is the state vector.
  returns the character of the chosen cell.
  Generally:
  locate=: second_strategy`first_strategy@.(first = mark)
  Simplified:
  locate=: human_locate NB. human versus human
)
locate=: human_locate`computer_locate@.(first = mark)

display=: show [: (1 1,:5 5)&(];.0)@:": [: <"0 fold

computer_locate=: [: show@{. board -. marks NB. strategy: first available
computer_locate=: [: show@({~ ?@:#) board -. marks NB. strategy: random

human_locate=: monad define
  state=. y
  m=. mark state
  b=. board state
  cells=. b -. marks state
  show '-->cell for ' , m , '?'
  whilst. cell -.@:e. cells do. cell =. {. (1!:1]1) , m end.
)

post=: 2&A.@:(3&{.)@:[ prepare mark@:[`((i.~ board)~)`(board@:[)}

mark=: {.                    NB. mark of the current player from state
marks=: 2&{.                 NB. extract both markers from state
board=: _9&{.                NB. extract board from state
first=: 2&{                  NB. extract first player from state

show=: [ smoutput

full=: 2 = #@:~.
won=: test@:fold
fold=: 3 3 $ board
test=: [: any [: all [: infix_pairs_agree |:@:lines

lines=: , diagonal , diagonal@:|. , |:
diagonal=: (<0 1)&|:
all=: *./
any=: +./
nor=: 8 b.
infix_pairs_agree=: 2&(=/\)

Java

This version works in the terminal itself, and uses the numpad for data entry. The computer is unbeatable, but some lines can be removed to avoid that. There's also an override that thrown in, just for fun.

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Hashtable;

public class TicTacToe
{
	public static void main(String[] args)
	{
		TicTacToe now=new TicTacToe();
		now.startMatch();
	}
	
	private int[][] marks;
	private int[][] wins;
	private int[] weights;
	private char[][] grid;
	private final int knotcount=3;
	private final int crosscount=4;
	private final int totalcount=5;
	private final int playerid=0;
	private final int compid=1;
	private final int truceid=2;
	private final int playingid=3;
	private String movesPlayer;
	private byte override;
	private char[][] overridegrid={{'o','o','o'},{'o','o','o'},{'o','o','o'}};
	private char[][] numpad={{'7','8','9'},{'4','5','6'},{'1','2','3'}};
	private Hashtable<Integer,Integer> crossbank;
	private Hashtable<Integer,Integer> knotbank;
	
	public void startMatch()
	{
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		System.out.print("Start?(y/n):");
		char choice='y';
		try
		{
			choice=br.readLine().charAt(0);
		}
		catch(Exception e)
		{
			System.out.println(e.getMessage());
		}
		if(choice=='n'||choice=='N')
		{
			return;
		}
		
		System.out.println("Use a standard numpad as an entry grid, as so:\n ");
		display(numpad);
		System.out.println("Begin");
		int playerscore=0;
		int compscore=0;
		do
		{
			int result=startGame();
			if(result==playerid)
				playerscore++;
			else if(result==compid)
				compscore++;
			System.out.println("Score: Player-"+playerscore+" AI-"+compscore);
			System.out.print("Another?(y/n):");
			try
			{
				choice=br.readLine().charAt(0);
			}
			catch(Exception e)
			{
				System.out.println(e.getMessage());
			}
			
		}while(choice!='n'||choice=='N');
		
		System.out.println("Game over.");
	}
	private void put(int cell,int player)
	{
		int i=-1,j=-1;;
		switch(cell)
		{
		case 1:i=2;j=0;break;
		case 2:i=2;j=1;break;
		case 3:i=2;j=2;break;
		case 4:i=1;j=0;break;
		case 5:i=1;j=1;break;
		case 6:i=1;j=2;break;
		case 7:i=0;j=0;break;
		case 8:i=0;j=1;break;
		case 9:i=0;j=2;break;
		default:display(overridegrid);return;
		}
		char mark='x';
		if(player==0)
			mark='o';
		grid[i][j]=mark;
		display(grid);
	}
	private int startGame()
	{
		init();
		display(grid);
		int status=playingid;
		while(status==playingid)
		{
			put(playerMove(),0);
			if(override==1)
			{
				System.out.println("O wins.");
				return playerid;
			}
			status=checkForWin();
			if(status!=playingid)
				break;
			try{Thread.sleep(1000);}catch(Exception e){System.out.print(e.getMessage());}
			put(compMove(),1);
			status=checkForWin();
		}
		return status;
	}
	private void init()
	{
		movesPlayer="";
		override=0;
		marks=new int[8][6];
		wins=new int[][]	//new int[8][3];
		{	
				{7,8,9},
				{4,5,6},
				{1,2,3},
				{7,4,1},
				{8,5,2},
				{9,6,3},
				{7,5,3},
				{9,5,1}
		};
		weights=new int[]{3,2,3,2,4,2,3,2,3};
		grid=new char[][]{{' ',' ',' '},{' ',' ',' '},{' ',' ',' '}};
		crossbank=new Hashtable<Integer,Integer>();
		knotbank=new Hashtable<Integer,Integer>();
	}
	private void mark(int m,int player)
	{
		for(int i=0;i<wins.length;i++)
			for(int j=0;j<wins[i].length;j++)
				if(wins[i][j]==m)
				{
					marks[i][j]=1;
					if(player==playerid)
						marks[i][knotcount]++;
					else
						marks[i][crosscount]++;
					marks[i][totalcount]++;
				}
	}
	private void fixWeights()
	{
		for(int i=0;i<3;i++)
			for(int j=0;j<3;j++)
				if(marks[i][j]==1)
					if(weights[wins[i][j]-1]!=Integer.MIN_VALUE)
						weights[wins[i][j]-1]=Integer.MIN_VALUE;
		
		for(int i=0;i<8;i++)
		{
			if(marks[i][totalcount]!=2)
				continue;
			if(marks[i][crosscount]==2)
			{
				int p=i,q=-1;
				if(marks[i][0]==0)
					q=0;
				else if(marks[i][1]==0)
					q=1;
				else if(marks[i][2]==0)
					q=2;
				
				if(weights[wins[p][q]-1]!=Integer.MIN_VALUE)
				{
					weights[wins[p][q]-1]=6;
				}
			}
			if(marks[i][knotcount]==2)
			{
				int p=i,q=-1;
				if(marks[i][0]==0)
					q=0;
				else if(marks[i][1]==0)
					q=1;
				else if(marks[i][2]==0)
					q=2;
				
				if(weights[wins[p][q]-1]!=Integer.MIN_VALUE)
				{
					weights[wins[p][q]-1]=5;
				}
			}
		}
	}
	private int compMove()
	{
		int cell=move();
		System.out.println("Computer plays: "+cell);
		//weights[cell-1]=Integer.MIN_VALUE;
		return cell;
	}
	private int move()
	{
		int max=Integer.MIN_VALUE;
		int cell=0;
		for(int i=0;i<weights.length;i++)
			if(weights[i]>max)
			{
				max=weights[i];
				cell=i+1;
			}
		
		//This section ensures the computer never loses
		//Remove it for a fair match
		//Dirty kluge
		if(movesPlayer.equals("76")||movesPlayer.equals("67"))
			cell=9;
		else if(movesPlayer.equals("92")||movesPlayer.equals("29"))
			cell=3;
		else if (movesPlayer.equals("18")||movesPlayer.equals("81"))
			cell=7;
		else if(movesPlayer.equals("73")||movesPlayer.equals("37"))
			cell=4*((int)(Math.random()*2)+1);
		else if(movesPlayer.equals("19")||movesPlayer.equals("91"))
			cell=4+2*(int)(Math.pow(-1, (int)(Math.random()*2)));
		
		mark(cell,1);
		fixWeights();
		crossbank.put(cell, 0);
		return cell;
	}
	private int playerMove()
	{
		System.out.print("What's your move?: ");
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		int cell=0;
		int okay=0;
		while(okay==0)
		{
			try
			{
				cell=Integer.parseInt(br.readLine());
			}
			catch(Exception e)
			{
				System.out.println(e.getMessage());
			}
			if(cell==7494)
			{
				override=1;
				return -1;
			}
			if((cell<1||cell>9)||weights[cell-1]==Integer.MIN_VALUE)
				System.out.print("Invalid move. Try again:");
			else
				okay=1;
		}
		playerMoved(cell);
		System.out.println();
		return cell;
	}
	private void playerMoved(int cell)
	{
		movesPlayer+=cell;
		mark(cell,0);
		fixWeights();
		knotbank.put(cell, 0);
	}
	private int checkForWin()
	{
		int crossflag=0,knotflag=0;
		for(int i=0;i<wins.length;i++)
		{
			if(crossbank.containsKey(wins[i][0]))
				if(crossbank.containsKey(wins[i][1]))
					if(crossbank.containsKey(wins[i][2]))
					{
						crossflag=1;
						break;
					}
			if(knotbank.containsKey(wins[i][0]))
				if(knotbank.containsKey(wins[i][1]))
					if(knotbank.containsKey(wins[i][2]))
					{
						knotflag=1;
						break;
					}
		}
		if(knotflag==1)
		{
			display(grid);
			System.out.println("O wins.");
			return playerid;
		}
		else if(crossflag==1)
		{
			display(grid);
			System.out.println("X wins.");
			return compid;
		}
		
		for(int i=0;i<weights.length;i++)
			if(weights[i]!=Integer.MIN_VALUE)
				return playingid;
		System.out.println("Truce");
		
		return truceid;
	}
	private void display(char[][] grid)
	{
		for(int i=0;i<3;i++)
		{
			System.out.println("\n-------");
			System.out.print("|");
			for(int j=0;j<3;j++)
				System.out.print(grid[i][j]+"|");
		}
		System.out.println("\n-------");
	}
}
Start?(y/n):y
Use a standard numpad as an entry grid, as so:
-------
|7|8|9|
-------
|4|5|6|
-------
|1|2|3|
-------
Begin

-------
| | | |
-------
| | | |
-------
| | | |
-------
What's your move?: 4

-------
| | | |
-------
|o| | |
-------
| | | |
-------

(...)

Computer plays: 7
-------
|x| |o|
-------
|o|x|o|
-------
|x|o|x|
-------
X wins.

Score: Player-0 AI-1
Another?(y/n):n
Game over.


This version uses javax.swing.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.logging.Logger;
/**

* TicTacToe Application
* @author Steve Robinson
* @version 1.0
*/
class TicTacToeFrame extends JFrame
{
 JButton [][] buttons= new JButton[3][3];
 JTextField statusBar;
 GamePanel panel;
 Integer turn;
 GameListener listener=new GameListener();
 Integer count;
 public TicTacToeFrame()
 {
setLayout(new BorderLayout());
  panel=new GamePanel();
  add(panel,BorderLayout.CENTER);
  statusBar=new JTextField("Player1's Turn");
  statusBar.setEditable(false);
  add(statusBar,BorderLayout.SOUTH);
  setTitle("Tic Tac Toe!");
  setVisible(true);
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  setBounds(400,400,300,300);
 }
 class GamePanel extends JPanel
 {
  public GamePanel()
  {
   setLayout(new GridLayout(3,3));
   turn =1;
   count=0;
   for(int i=0;i<3;i++)
    for(int j=0;j<3;j++)   {
     buttons[i][j]=new JButton();
     buttons[i][j].putClientProperty("INDEX", new Integer[]{i,j});
     buttons[i][j].putClientProperty("OWNER", null);
     buttons[i][j].addActionListener(listener);
     add(buttons[i][j]);
    }
  }
 }
 class GameListener implements ActionListener
 {
  public void actionPerformed(ActionEvent e)
  {
   count++;
   JButton b=(JButton)e.getSource();
   Integer[]index=(Integer[]) b.getClientProperty("INDEX");
   //System.out.println(turn); //turn                  //   //System.out.println("["+index[0]+"]"+"["+index[1]+"]");         //
   b.putClientProperty("OWNER", turn);
   Icon ico=new ImageIcon(turn.toString()+".gif");
   b.setIcon(ico);
   b.setEnabled(false);
   boolean result=checkVictoryCondition(index);
   if(result)
   {
    JOptionPane.showMessageDialog(null, "Player "+turn.toString()+" Wins");
    initComponents();
   }
   else
   {
    if(turn==1)
    {
     turn=2;
     statusBar.setText("Player2's Turn");
    }
    else
    {
     turn=1;
     statusBar.setText("Player1's Turn");
    }
   }
   if(count==9)
   {
    JOptionPane.showMessageDialog(null, "Match is a draw!");
    initComponents();
   }
  }
  Integer getOwner(JButton b)
  {
   return (Integer)b.getClientProperty("OWNER");
  }
  //PrintButtonMap for Diagnostics
  void printbuttonMap(Integer [][]bMap)
  {
   for(int i=0;i    for(int j=0;j     System.out.print(bMap[i][j]+" ");
    System.out.println("");
   }
  }
  boolean checkVictoryCondition(Integer [] index)
  {
   /*Integer[][]buttonMap=new Integer[][] {

     { getOwner(buttons[0][0]),getOwner(buttons[0][1]),getOwner(buttons[0][2])},

     { getOwner(buttons[1][0]),getOwner(buttons[1][1]),getOwner(buttons[1][2])},

     { getOwner(buttons[2][0]),getOwner(buttons[2][1]),getOwner(buttons[2][2])}
   };
   printbuttonMap(buttonMap); */
   Integer a=index[0];
                Integer b=index[1];
   int i;
   //check row
   for(i=0;i<3;i++)  {
    if(getOwner(buttons[a][i])!=getOwner(buttons[a][b]))
     break;
   }
   if(i==3)
    return true;
   //check column
   for(i=0;i<3;i++)  {
    if(getOwner(buttons[i][b])!=getOwner(buttons[a][b]))
     break;
   }
   if(i==3)
    return true;
   //check diagonal
   if((a==2&&b==2)||(a==0&&b==0)||(a==1&&b==1)||(a==0&&b==2)||(a==2&&b==0))
   {
    //left diagonal
    for(i=0;i     if(getOwner(buttons[i][i])!=getOwner(buttons[a][b]))
      break;
    if(i==3)
     return true;
    //right diagonal
    if((getOwner(buttons[0][2])==getOwner(buttons[a][b]))&&(getOwner(buttons[1][1])==getOwner(buttons[a][b]))&&(getOwner(buttons[2][0])==getOwner(buttons[a][b])))
     return true;
    }
   return false;
  }
 }
 void initComponents()
 {
  for(int i=0;i<3;i++)  
   for(int j=0;j<3;j++)  {
    buttons[i][j].putClientProperty("INDEX", new Integer[]{i,j});
    buttons[i][j].putClientProperty("OWNER",null);
    buttons[i][j].setIcon(null);
    buttons[i][j].setEnabled(true);
    turn=1;
    count=0;
    statusBar.setText("Player1's Turn");
   }
 }
}
class TicTacToe {
 public static void main(String[] args) {
  EventQueue.invokeLater(new Runnable(){
   public void run()
   {
    TicTacToeFrame frame=new TicTacToeFrame();
   }
  });
 }
}

Graphical Java Example

import javax.swing.*;
import java.awt.event.*;
import java.awt.*;


//Make sure the name of the class is the same as the .java file name.
//If you change the class name you should change the class object name in runGUI method
public class ticTacToeCallum implements ActionListener {
 
  static JFrame frame;          
  static JPanel contentPane;    
  static JLabel lblEnterFirstPlayerName, lblEnterSecondPlayerName, lblFirstPlayerScore, lblSecondPlayerScore;    
  static JButton btnButton1, btnButton2, btnButton3, btnButton4, btnButton5, btnButton6, btnButton7, btnButton8, btnButton9, btnClearBoard, btnClearAll, btnCloseGame;     
  static JTextField txtEnterFirstPlayerName, txtEnterSecondPlayerName;  
  static Icon imgicon = new ImageIcon("saveIcon.JPG");

  Font buttonFont = new Font("Arial", Font.PLAIN, 20);
  
  
  //to adjust the frame size change the values in pixels
  static int width = 600;
  static int length = 400;
  static int firstPlayerScore = 0;
  static int secondPlayerScore = 0;
  static int playerTurn = 1;
  static int roundComplete = 0;
  static int button1 = 1, button2 = 1, button3 = 1, button4 = 1, button5 = 1, button6 = 1, button7 = 1, button8 = 1, button9 = 1; // 1 is true, 0 is false
  

  public ticTacToeCallum(){
	  
    frame = new JFrame("Tic Tac Toe ^_^");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    
    contentPane = new JPanel();
    contentPane.setLayout(new GridLayout(6, 3, 10, 10));
    contentPane.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
   
    btnButton1 = new JButton("");
    btnButton1.setFont(buttonFont);
    btnButton1.setAlignmentX(JButton.CENTER_ALIGNMENT);
    btnButton1.setIcon(imgicon);
    btnButton1.setActionCommand("CLICK1");    
    btnButton1.addActionListener(this);  
    contentPane.add(btnButton1);
    
    btnButton2 = new JButton("");
    btnButton2.setFont(buttonFont);
    btnButton2.setAlignmentX(JButton.CENTER_ALIGNMENT);
    btnButton2.setIcon(imgicon);
    btnButton2.setActionCommand("CLICK2");    
    btnButton2.addActionListener(this);      
    contentPane.add(btnButton2);
    
    btnButton3 = new JButton(""); 
    btnButton3.setFont(buttonFont);
    btnButton3.setAlignmentX(JButton.CENTER_ALIGNMENT);
    btnButton3.setIcon(imgicon);
    btnButton3.setActionCommand("CLICK3");    
    btnButton3.addActionListener(this);      
    contentPane.add(btnButton3);
    
    btnButton4 = new JButton("");
    btnButton4.setFont(buttonFont);
    btnButton4.setAlignmentX(JButton.CENTER_ALIGNMENT);
    btnButton4.setIcon(imgicon);
    btnButton4.setActionCommand("CLICK4");    
    btnButton4.addActionListener(this);      
    contentPane.add(btnButton4);
    
    btnButton5 = new JButton(""); 
    btnButton5.setFont(buttonFont);
    btnButton5.setAlignmentX(JButton.CENTER_ALIGNMENT);
    btnButton5.setIcon(imgicon);
    btnButton5.setActionCommand("CLICK5");    
    btnButton5.addActionListener(this);      
    contentPane.add(btnButton5);
    
    btnButton6 = new JButton(""); 
    btnButton6.setFont(buttonFont);
    btnButton6.setAlignmentX(JButton.CENTER_ALIGNMENT);
    btnButton6.setIcon(imgicon);
    btnButton6.setActionCommand("CLICK6");    
    btnButton6.addActionListener(this);      
    contentPane.add(btnButton6);
    
    btnButton7 = new JButton(""); 
    btnButton7.setFont(buttonFont);
    btnButton7.setAlignmentX(JButton.CENTER_ALIGNMENT);
    btnButton7.setIcon(imgicon);
    btnButton7.setActionCommand("CLICK7");    
    btnButton7.addActionListener(this);      
    contentPane.add(btnButton7);
    
    btnButton8 = new JButton(""); 
    btnButton8.setFont(buttonFont);
    btnButton8.setAlignmentX(JButton.CENTER_ALIGNMENT);
    btnButton8.setIcon(imgicon);
    btnButton8.setActionCommand("CLICK8");    
    btnButton8.addActionListener(this);      
    contentPane.add(btnButton8);
    
    btnButton9 = new JButton("");
    btnButton9.setFont(buttonFont);
    btnButton9.setAlignmentX(JButton.CENTER_ALIGNMENT);
    btnButton9.setIcon(imgicon);
    btnButton9.setActionCommand("CLICK9");    
    btnButton9.addActionListener(this);      
    contentPane.add(btnButton9);
    
    lblEnterFirstPlayerName = new JLabel("Enter First Player's Name");
    contentPane.add(lblEnterFirstPlayerName);
    
    txtEnterFirstPlayerName = new JTextField("");
    contentPane.add(txtEnterFirstPlayerName);
    
    lblFirstPlayerScore = new JLabel("Score: " + firstPlayerScore);
    contentPane.add(lblFirstPlayerScore);
    
    lblEnterSecondPlayerName = new JLabel("Enter Second Player's Name");
    contentPane.add(lblEnterSecondPlayerName);
    
    txtEnterSecondPlayerName = new JTextField("");
    contentPane.add(txtEnterSecondPlayerName);
    
    lblSecondPlayerScore = new JLabel("Score: " + secondPlayerScore);
    contentPane.add(lblSecondPlayerScore);
    
    btnClearBoard = new JButton("Clear Board");  
    btnClearBoard.setAlignmentX(JButton.CENTER_ALIGNMENT);
    btnClearBoard.setIcon(imgicon);
    btnClearBoard.setActionCommand("CLICKClearBoard");    
    btnClearBoard.addActionListener(this);      
    contentPane.add(btnClearBoard);
    
    btnClearAll = new JButton("Clear All");  
    btnClearAll.setAlignmentX(JButton.CENTER_ALIGNMENT);
    btnClearAll.setIcon(imgicon);
    btnClearAll.setActionCommand("CLICKClearAll");    
    btnClearAll.addActionListener(this);      
    contentPane.add(btnClearAll);
    
    btnCloseGame = new JButton("Close Game"); 
    btnCloseGame.setAlignmentX(JButton.CENTER_ALIGNMENT);
    btnCloseGame.setIcon(imgicon);
    btnCloseGame.setActionCommand("CLICKCloseGame");    
    btnCloseGame.addActionListener(this);      
    contentPane.add(btnCloseGame);
    
    frame.setContentPane(contentPane);
    frame.pack();
    frame.setSize(width,length);
    frame.setVisible(true);

  }

  public void actionPerformed(ActionEvent event) {
    String eventName = event.getActionCommand();
     if (eventName.equals("CLICK1")) {
    	 if (button1 == 1){
    		 if (playerTurn == 1){
    			 btnButton1.setForeground(Color.RED);
    			 btnButton1.setText("X");
   	  			 playerTurn = 2;
    			 button1 = 0;
    		 } else if (playerTurn == 2) {
    			 btnButton1.setForeground(Color.GREEN);
    			 btnButton1.setText("O");
    			 playerTurn = 1;
    			 button1 = 0;
    		 }
    	 }
      } else if (eventName.equals ("CLICK2")) {
    	  if (button2 == 1){	
    	  	if (playerTurn == 1){
    	  		btnButton2.setForeground(Color.RED);
    	  		btnButton2.setText("X");
  	  			playerTurn = 2;
    	  		button2 = 0;
    	  	} else if (playerTurn == 2) {
    	  		btnButton2.setForeground(Color.GREEN);
    	  		btnButton2.setText("O");
    	  		playerTurn = 1;
    	  		button2 = 0;
    	  	}
    	  }	
      }	else if (eventName.equals ("CLICK3")) {
    	  if (button3 == 1){	
      	  	if (playerTurn == 1){
      	  		btnButton3.setForeground(Color.RED);
      	  		btnButton3.setText("X");
  	  			playerTurn = 2;
      	  		button3 = 0;
      	  	} else if (playerTurn == 2) {
      	  		btnButton3.setForeground(Color.GREEN);
      	  		btnButton3.setText("O");
      	  		playerTurn = 1;
      	  		button3 = 0;
      	  	}
      	  }
      }	else if (eventName.equals ("CLICK4")) {
    	  if (button4 == 1){	
      	  	if (playerTurn == 1){
      	  		btnButton4.setForeground(Color.RED);
      	  		btnButton4.setText("X");
  	  			playerTurn = 2;
      	  		button4 = 0;
      	  	} else if (playerTurn == 2) {
      	  		btnButton4.setForeground(Color.GREEN);
      	  		btnButton4.setText("O");
      	  		playerTurn = 1;
      	  		button4 = 0;
      	  	}
      	  }
      }	else if (eventName.equals ("CLICK5")) {
    	  if (button5 == 1){	
      	  	if (playerTurn == 1){
      	  		btnButton5.setForeground(Color.RED);
  	  			btnButton5.setText("X");
  	  			playerTurn = 2;
  	  			button5 = 0;
      	  	} else if (playerTurn == 2) {
      	  		btnButton5.setForeground(Color.GREEN);
  	  			btnButton5.setText("O");
  	  			playerTurn = 1;
  	  			button5 = 0;
      	  	}
      	  }
      } else if (eventName.equals ("CLICK6")) {
    	  if (button6 == 1){	
      	  	if (playerTurn == 1){
      	  		btnButton6.setForeground(Color.RED);
  	  			btnButton6.setText("X");
  	  			playerTurn = 2;
  	  			button6 = 0;
      	  	} else if (playerTurn == 2) {
      	  		btnButton6.setForeground(Color.GREEN);
  	  			btnButton6.setText("O");
  	  			playerTurn = 1;
  	  			button6 = 0;
      	  	}
      	  }
      } else if (eventName.equals ("CLICK7")) {
    	  if (button7 == 1){	
      	  	if (playerTurn == 1){
      	  		btnButton7.setForeground(Color.RED);
  	  			btnButton7.setText("X");
  	  			playerTurn = 2;
  	  			button7 = 0;
      	  	} else if (playerTurn == 2) {
      	  		btnButton7.setForeground(Color.GREEN);
  	  			btnButton7.setText("O");
  	  			playerTurn = 1;
  	  			button7 = 0;
      	  	}
      	  }
      } else if (eventName.equals ("CLICK8")) {
    	  if (button8 == 1){	
      	  	if (playerTurn == 1){
      	  		btnButton8.setForeground(Color.RED);
  	  			btnButton8.setText("X");
  	  			playerTurn = 2;
  	  			button8 = 0;
      	  	} else if (playerTurn == 2) {
      	  		btnButton8.setForeground(Color.GREEN);
  	  			btnButton8.setText("O");
  	  			playerTurn = 1;
  	  			button8 = 0;
      	  	}
      	  }
      } else if (eventName.equals ("CLICK9")) {
    	  if (button9 == 1){	
      	  	if (playerTurn == 1){
      	  		btnButton9.setForeground(Color.RED);
  	  			btnButton9.setText("X");
  	  			playerTurn = 2;
  	  			button9 = 0;
      	  	} else if (playerTurn == 2) {
      	  		btnButton9.setForeground(Color.GREEN);
  	  			btnButton9.setText("O");
  	  			playerTurn = 1;
  	  			button9 = 0;
      	  	}
      	  }
      } else if (eventName.equals ("CLICKClearBoard")) {
          
    	  btnButton1.setText("");
          btnButton2.setText("");
          btnButton3.setText("");
          btnButton4.setText("");
          btnButton5.setText("");
          btnButton6.setText("");
          btnButton7.setText("");
          btnButton8.setText("");
          btnButton9.setText("");
          
          button1 = 1;
          button2 = 1;
          button3 = 1;
          button4 = 1;
          button5 = 1;
          button6 = 1;
          button7 = 1;
          button8 = 1;
          button9 = 1;
          
          playerTurn = 1;
          
          roundComplete = 0;
          
      } else if (eventName.equals ("CLICKClearAll")) {
    	  
    	  btnButton1.setText("");
          btnButton2.setText("");
          btnButton3.setText("");
          btnButton4.setText("");
          btnButton5.setText("");
          btnButton6.setText("");
          btnButton7.setText("");
          btnButton8.setText("");
          btnButton9.setText("");
          
          firstPlayerScore = 0;
          lblFirstPlayerScore.setText("Score: " + firstPlayerScore);
          secondPlayerScore = 0;
          lblSecondPlayerScore.setText("Score: " + secondPlayerScore);
          
          txtEnterFirstPlayerName.setText("");
          txtEnterSecondPlayerName.setText("");
          
          button1 = 1;
          button2 = 1;
          button3 = 1;
          button4 = 1;
          button5 = 1;
          button6 = 1;
          button7 = 1;
          button8 = 1;
          button9 = 1;
         
          playerTurn = 1;
          
          roundComplete = 0;
          
      } else if (eventName.equals ("CLICKCloseGame")) {
    	  System.exit(0);
      }  
     score();
    }
  
  
  public static void score(){
	  if (roundComplete == 0){
	  if (btnButton1.getText().equals(btnButton2.getText())  && btnButton1.getText().equals(btnButton3.getText())){
	    	if (btnButton1.getText().equals("X")){
	    		firstPlayerScore += 1;
	    		lblFirstPlayerScore.setText("Score: " + firstPlayerScore);
	    		roundComplete = 1;
	    	} else if (btnButton1.getText().equals("O")){
	    		secondPlayerScore += 1;
	    		lblSecondPlayerScore.setText("Score: " + secondPlayerScore);
	    		roundComplete = 1;
	    	}
	    }
	    if (btnButton1.getText().equals(btnButton4.getText())  && btnButton1.getText().equals(btnButton7.getText())){
	    	if (btnButton1.getText().equals("X")){
	    		firstPlayerScore += 1;
	    		lblFirstPlayerScore.setText("Score: " + firstPlayerScore);
	    		roundComplete = 1;
	    	} else if (btnButton1.getText().equals("O")){
	    		secondPlayerScore += 1;
	    		lblSecondPlayerScore.setText("Score: " + secondPlayerScore);
	    		roundComplete = 1;
	    	}
	    }
	    if (btnButton1.getText().equals(btnButton5.getText())  && btnButton1.getText().equals(btnButton9.getText())){
	    	if (btnButton1.getText().equals("X")){
	    		firstPlayerScore += 1;
	    		lblFirstPlayerScore.setText("Score: " + firstPlayerScore);
	    		roundComplete = 1;
	    	} else if (btnButton1.getText().equals("O")){
	    		secondPlayerScore += 1;
	    		lblSecondPlayerScore.setText("Score: " + secondPlayerScore);
	    		roundComplete = 1;
	    	}
	    }
	    if (btnButton7.getText().equals(btnButton8.getText())  && btnButton7.getText().equals(btnButton9.getText())){
	    	if (btnButton7.getText().equals("X")){
	    		firstPlayerScore += 1;
	    		lblFirstPlayerScore.setText("Score: " + firstPlayerScore);
	    		roundComplete = 1;
	    	} else if (btnButton7.getText().equals("O")){
	    		secondPlayerScore += 1;
	    		lblSecondPlayerScore.setText("Score: " + secondPlayerScore);
	    		roundComplete = 1;
	    	}
	    }
	    if (btnButton7.getText().equals(btnButton5.getText())  && btnButton7.getText().equals(btnButton3.getText())){
	    	if (btnButton7.getText().equals("X")){
	    		firstPlayerScore += 1;
	    		lblFirstPlayerScore.setText("Score: " + firstPlayerScore);
	    		roundComplete = 1;
	    	} else if (btnButton7.getText().equals("O")){
	    		secondPlayerScore += 1;
	    		lblSecondPlayerScore.setText("Score: " + secondPlayerScore);
	    		roundComplete = 1;
	    	}
	    }
	    if (btnButton3.getText().equals(btnButton6.getText())  && btnButton3.getText().equals(btnButton9.getText())){
	    	if (btnButton3.getText().equals("X")){
	    		firstPlayerScore += 1;
	    		lblFirstPlayerScore.setText("Score: " + firstPlayerScore);
	    		roundComplete = 1;
	    	} else if (btnButton3.getText().equals("O")){
	    		secondPlayerScore += 1;
	    		lblSecondPlayerScore.setText("Score: " + secondPlayerScore);
	    		roundComplete = 1;
	    	}
	    }
	    if (btnButton4.getText().equals(btnButton5.getText())  && btnButton4.getText().equals(btnButton6.getText())){
	    	if (btnButton4.getText().equals("X")){
	    		firstPlayerScore += 1;
	    		lblFirstPlayerScore.setText("Score: " + firstPlayerScore);
	    		roundComplete = 1;
	    	} else if (btnButton4.getText().equals("O")){
	    		secondPlayerScore += 1;
	    		lblSecondPlayerScore.setText("Score: " + secondPlayerScore);
	    		roundComplete = 1;
	    	}
	    }
	    if (btnButton2.getText().equals(btnButton5.getText())  && btnButton2.getText().equals(btnButton8.getText())){
	    	if (btnButton2.getText().equals("X")){
	    		firstPlayerScore += 1;
	    		lblFirstPlayerScore.setText("Score: " + firstPlayerScore);
	    		roundComplete = 1;
	    	} else if (btnButton2.getText().equals("O")){
	    		secondPlayerScore += 1;
	    		lblSecondPlayerScore.setText("Score: " + secondPlayerScore);
	    		roundComplete = 1;
	    	}
	    }