# 21 Game

21 Game is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

21   is a two player game,   the game is played by choosing a number   (1,   2,   or   3)   to be added to the   running total.

The game is won by the player whose chosen number causes the   running total   to reach   exactly   21.
The   running total   starts at zero.

One player will be the computer.   Players alternate supplying a number to be added to the   running total.

Task

Write a computer program that will:

•   do the prompting   (or provide a button menu),
•   check for errors and display appropriate error messages,
•   do the additions   (add a chosen number to the   running total),
•   display the   running total,
•   provide a mechanism for the player to   quit/exit/halt/stop/close   the program,
•   issue a notification when there is a winner,   and
•   determine who goes first   (possibly a random choice, or it can be specified when the game begins).

## Go

To give the human player a reasonable chance whoever goes first, the computer always chooses randomly when the running total is below 18 but otherwise chooses the exact number needed to win the game.

`package main import (    "bufio"    "fmt"    "log"    "math/rand"    "os"    "strconv"    "time") var scanner = bufio.NewScanner(os.Stdin) var (    total = 0    quit  = false) func itob(i int) bool {    if i == 0 {        return false    }    return true} func getChoice() {    for {        fmt.Print("Your choice 1 to 3 : ")        scanner.Scan()        if scerr := scanner.Err(); scerr != nil {            log.Fatalln(scerr, "when choosing number")        }        text := scanner.Text()        if text == "q" || text == "Q" {            quit = true            return        }        input, err := strconv.Atoi(text)        if err != nil {            fmt.Println("Invalid number, try again")            continue        }        newTotal := total + input        switch {        case input < 1 || input > 3:            fmt.Println("Out of range, try again")        case newTotal > 21:            fmt.Println("Too big, try again")        default:            total = newTotal            fmt.Println("Running total is now", total)            return        }    }} func main() {    rand.Seed(time.Now().UnixNano())    computer := itob(rand.Intn(2))    fmt.Println("Enter q to quit at any time\n")    if computer {        fmt.Println("The computer will choose first")    } else {        fmt.Println("You will choose first")    }    fmt.Println("\nRunning total is now 0\n")    var choice int    for round := 1; ; round++ {        fmt.Printf("ROUND %d:\n\n", round)        for i := 0; i < 2; i++ {            if computer {                if total < 18 {                    choice = 1 + rand.Intn(3)                } else {                    choice = 21 - total                }                total += choice                fmt.Println("The computer chooses", choice)                fmt.Println("Running total is now", total)                if total == 21 {                    fmt.Println("\nSo, commiserations, the computer has won!")                    return                }            } else {                getChoice()                if quit {                    fmt.Println("OK, quitting the game")                    return                }                if total == 21 {                    fmt.Println("\nSo, congratulations, you've won!")                    return                }            }            fmt.Println()            computer = !computer        }    }}`
Output:

A sample game where the human player manages to win even though the computer (chosen randomly) goes first.

```Enter q to quit at any time

The computer will choose first

Running total is now 0

ROUND 1:

The computer chooses 1
Running total is now 1

Your choice 1 to 3 : 3
Running total is now 4

ROUND 2:

The computer chooses 2
Running total is now 6

Your choice 1 to 3 : 4
Out of range, try again
Your choice 1 to 3 : 3
Running total is now 9

ROUND 3:

The computer chooses 2
Running total is now 11

Your choice 1 to 3 : 2
Running total is now 13

ROUND 4:

The computer chooses 2
Running total is now 15

Your choice 1 to 3 : 2
Running total is now 17

ROUND 5:

The computer chooses 1
Running total is now 18

Your choice 1 to 3 : 3
Running total is now 21

So, congratulations, you've won!
```

A sample game where the human player plays sensibly but still loses when the computer goes first.

```Enter q to quit at any time

The computer will choose first

Running total is now 0

ROUND 1:

The computer chooses 3
Running total is now 3

Your choice 1 to 3 : 3
Running total is now 6

ROUND 2:

The computer chooses 3
Running total is now 9

Your choice 1 to 3 : 3
Running total is now 12

ROUND 3:

The computer chooses 1
Running total is now 13

Your choice 1 to 3 : 3
Running total is now 16

ROUND 4:

The computer chooses 1
Running total is now 17

Your choice 1 to 3 : 1
Running total is now 18

ROUND 5:

The computer chooses 3
Running total is now 21

So, commiserations, the computer has won!
```

## Julia

The computer or player can always win if they go first and choose a number that brings the total to one of the following: 1, 5, 9, 13, or 17. To make things vary more, there is a choice of computer play level at the start. The computer will randomly respond with level 1 and choose a random response 1/4 of the time at level 2.

` function trytowin(n)    if 21 - n < 4        println("Computer chooses \$(21 - n) and wins. GG!")        exit(0)    endend function choosewisely(n)    trytowin(n)    targets = [1, 5, 9, 13, 17, 21]    pos = findfirst(x -> x > n, targets)    bestmove = targets[pos] - n    if bestmove > 3        println("Looks like I could lose. Choosing a 1, total now \$(n + 1).")        return n + 1    end    println("On a roll, choosing a \$bestmove, total now \$(n + bestmove).")    n + bestmoveend function choosefoolishly(n)    trytowin(n)    move = rand([1, 2, 3])    println("Here goes, choosing \$move, total now \$(n + move).")    n + moveend function choosesemiwisely(n)    trytowin(n)    if rand() > 0.75        choosefoolishly(n)    else        choosewisely(n)    endend prompt(s) = (println(s, ": => "); return readline()) function playermove(n)    rang = (n > 19) ? "1 is all" : ((n > 18) ? "1 or 2" : "1, 2 or 3")    choice = 0    while true        nstr = prompt("Your choice (\$rang), 0 to exit")        if nstr == "0"            exit(0)        elseif nstr == "1"            return n + 1        elseif nstr == "2" && n < 20            return n + 2        elseif nstr == "3" && n < 19            return n + 3        end    endend  function play21game()    n = 0    level = prompt("Level of play (1=dumb, 3=smart)")    algo = choosewisely    if level == "1"        algo = choosefoolishly    elseif level == "2"        algo = choosesemiwisely    elseif level != "3"        println("Bad choice syntax--default to smart choice")    end    whofirst = prompt("Does computer go first? (y or n)")    if whofirst == 'y' || whofirst == 'Y'        n = algo(n)    end    while n < 21        n = playermove(n)        if n == 21            println("Player wins! Game over, gg!")            break        end        n = algo(n)    endend play21game() `

## Perl

Translation of: Perl 6
`print <<'HERE';The 21 game. Each player chooses to add 1, 2, or 3 to a running total.The player whose turn it is when the total reaches 21 wins. Enter q to quit.HERE my \$total = 0; while () {    print "Running total is: \$total\n";    my (\$me,\$comp);    while () {        print 'What number do you play> ';        \$me = <>; chomp \$me;        last if \$me =~ /^\$/;        insult(\$me);    }    \$total += \$me;    win('Human') if \$total >= 21;    print "Computer plays: " . (\$comp = 1+int(rand(3))) . "\n";    \$total += \$comp;    win('Computer') if \$total >= 21;} sub win {    my(\$player) = @_;    print "\$player wins.\n";    exit;} sub insult {    my(\$g) = @_;    exit if \$g =~ /q/i;    my @insults = ('Yo mama', 'Jeez', 'Ummmm', 'Grow up');    my \$i = \$insults[1+int rand(\$#insults)];    print "\$i, \$g is not an integer between 1 and 3...\n"}`
Output:
```The 21 game. Each player chooses to add 1, 2, or 3 to a running total.
The player whose turn it is when the total reaches 21 wins. Enter q to quit.
Running total is: 0
What number do you play> 3
Computer plays: 3
Running total is: 6
What number do you play> 3
Computer plays: 3
Running total is: 12
What number do you play> 3
Computer plays: 2
Running total is: 17
What number do you play> 1
Computer plays: 1
Running total is: 19
What number do you play> 2
Human wins.```

## Perl 6

Works with: Rakudo version 2018.09

Since there is no requirement that the computer play sensibly, it always plays a random guess so the player has some chance to win.

`say qq :to 'HERE';    The 21 game. Each player chooses to add 1, 2, or 3 to a running total.    The player whose turn it is when the total reaches 21 wins. Enter q to quit.    HERE my \$total = 0;loop {    say "Running total is: \$total";    my (\$me,\$comp);    loop {        \$me = prompt 'What number do you play> ';        last if \$me ~~ /^<>\$/;        insult \$me;    }    \$total += \$me;    win('Human') if \$total >= 21;    say "Computer plays: { \$comp = (1,2,3).roll }\n";    \$total += \$comp;    win('Computer') if \$total >= 21;} sub win (\$player) {    say "\$player wins.";    exit;} sub insult (\$g) {    exit if \$g eq 'q';    print ('Yo mama,', 'Jeez,', 'Ummmm,', 'Grow up,', 'Did you even READ the instructions?').roll;    say " \$g is not an integer between 1 & 3..."}`
Sample game:
```The 21 game. Each player chooses to add 1, 2, or 3 to a running total.
The player whose turn it is when the total reaches 21 wins. Enter q to quit.

Running total is: 0
What number do you play> 5
Did you even READ the instructions? 5 is not an integer between 1 & 3...
What number do you play> g
Yo mama, g is not an integer between 1 & 3...
What number do you play> 12
Jeez, 12 is not an integer between 1 & 3...
What number do you play> 3
Computer plays: 2

Running total is: 5
What number do you play> 3
Computer plays: 3

Running total is: 11
What number do you play> 1
Computer plays: 1

Running total is: 13
What number do you play> 3
Computer plays: 2

Running total is: 18
What number do you play> 3
Human wins.```

## Phix

If the computer goes first you cannot win.
Once the computer stops displaying "no clear strategy" you cannot win.
The computer_first flag only applies to the first game. After winning, losing, or conceding, you go first.

`bool computer_first = falsebool show_spoiler = false integer total = 0 procedure computer_play()    integer move = 0    for i=1 to 3 do        if mod(total+i,4)=1 then            move = i            exit        end if    end for    if move=0 then        puts(1,"no clear strategy\n")        move = rand(min(3,21-total))    end if    printf(1,"Total is %d. I play %d.\n",{total,move})    total += move    if total=21 then        puts(1,"21! I win!\n")    end ifend procedure puts(1,"\n21 game\n\n")puts(1,"Press escape or q to quit the game, c to concede and start a new game from 0\n\n") if computer_first then    printf(1,"Total is %d.\n",{total})      computer_play()elsif show_spoiler then    -- The secret to winning!    puts(1,sq_sub("Uif!pomz!xbz!up!xjo!jt!qmbz!2!gjstu-!uifo!5.=dpnqvufs!npwf?!fwfsz!ujnf",1)&"\n\n")end if while 1 do    printf(1,"Total is %d. enter 1, 2, or 3: ",{total})    integer ch = wait_key()    puts(1,iff(ch=#1B?"esc":ch)&"\n")    if ch>='1' and ch<='3' then        ch -= '0'        if total+ch>21 then            puts(1,"Too big\n")        else            total += ch            if total=21 then                puts(1,"21! You win!\n")            else                computer_play()            end if        end if    elsif ch=#1B or lower(ch)='q' then        puts(1,"Quitting\n")        exit    end if    if lower(ch)='c' or total=21 then        total = 0    end ifend while`
Output:
```21 game

Press escape or q to quit the game, c to concede and start a new game from 0

Total is 0. enter 1, 2, or 3: 1
no clear strategy
Total is 1. I play 3.
Total is 4. enter 1, 2, or 3: 1
no clear strategy
Total is 5. I play 1.
Total is 6. enter 1, 2, or 3: 3
no clear strategy
Total is 9. I play 1.
Total is 10. enter 1, 2, or 3: 1
Total is 11. I play 2.
Total is 13. enter 1, 2, or 3: 3
Total is 16. I play 1.
Total is 17. enter 1, 2, or 3: 2
Total is 19. I play 2.
21! I win!
Total is 0. enter 1, 2, or 3: q
Quitting
```

## REXX

Around half of the REXX program deals with incorrect or missing input   (of the required integer).

`/*REXX program plays the  21  game with a human,  each player chooses 1, 2, or 3  which *//*──────────── is added to the current sum, the first player to reach  21  exactly wins.*/sep= copies('─', 8);  sep2= " "copies('═', 8)" " /*construct an eye─catching msg fences.*/say sep 'Playing the  21  game.'                 /*tell what's happening here at the zoo*/high=  3                                         /*the highest integer that can be used.*/game= 21                                         /*the game target  (winning total/sum).*/\$= 0                                             /*the sum [or running total]  (so far).*/    do j=1  while \$<game;     bad= 0             /*obtain optional move from ARG or ask.*/    low = (j \== 1)                              /*allow user to have computer go first.*/    say;     say sep  'Please enter a number from ' low " ───► 3               (or Quit):"    if j==1  then say sep '[A value of 0 (zero) means you want the computer to go first.]'    pull x _ . 1 ax                              /*obtain an uppercased answer & others.*/    if   x=''             then call ser "Nothing entered."    if _\==''             then call ser "Too many arguments entered: "       ax    if abbrev('QUIT', x, 1)  then do;   say;      say sep  "quitting.";      exit 1                                  end    if \datatype(x, 'N')  then call ser "Argument isn't numeric: "            x    if \datatype(x, 'W')  then call ser "Number isn't an integer: "           x    if x<0                then call ser "Number can't be negative: "          x    if x=0  &  j>1        then call ser "Number can't be zero: "              x    if x>high             then call ser "Number is too large  (>"high'): '    x    if bad                then iterate           /*Had an error? Then get another number*/    x= x / 1                                     /*normalize the  X  number;  +2 001 3. */    if \$+x > game         then call ser "Number will cause the sum to exceed " g': '   x    if x\==0              then call tot x, 1     /*Not 0?   The user wants to go first. */    if \$==game            then leave             /*the user won the game with the last #*/    y=.                                          /*indicate that no choice has been made*/         do c=1  for high  until y\==.           /*find a # that yields the best choice.*/         if (c+\$) // (1+high) == 1  then y= c    /*a bit of a highfalutin calculation.  */         end   /*c*/    if y==.  then y= random(1, high)             /*get random choice (maybe a lost game)*/    say sep 'The computer chooses '     y     " as it's choice."        /*inform player.*/    call tot y, 0                                /*call subroutine to show the total.   */    end   /*j*/sayif who  then say sep  'Congratulations!   You have won the  21  game.'        else say sep  'The computer has won the  21  game.'exit 0                                           /*stick a fork in it,  we're all done. *//*──────────────────────────────────────────────────────────────────────────────────────*/ser: if bad  then return;  bad=1;  say;  say;  say sep '***error***' arg(1);  say;  returntot: arg q,who; \$=\$+q; say sep 'The game total is now' sep2 \$ sep2; return /*add; show \$*/`
output:
```──────── Playing the  21  game.

──────── Please enter a number from  0 ───► 3               (or Quit):
──────── [A value of 0 (zero) means you want the computer to go first.]
3                                                                         ◄■■■■■■■■■■ user input
──────── The game total is now  ════════  3  ════════
──────── The computer chooses  1  as it's choice.
──────── The game total is now  ════════  4  ════════

──────── Please enter a number from  1 ───► 3               (or Quit):
3                                                                          ◄■■■■■■■■■■ user input
──────── The game total is now  ════════  7  ════════
──────── The computer chooses  1  as it's choice.
──────── The game total is now  ════════  8  ════════

──────── Please enter a number from  1 ───► 3               (or Quit):
3                                                                          ◄■■■■■■■■■■ user input
──────── The game total is now  ════════  11  ════════
──────── The computer chooses  1  as it's choice.
──────── The game total is now  ════════  12  ════════

──────── Please enter a number from  1 ───► 3               (or Quit):
3                                                                          ◄■■■■■■■■■■ user input
──────── The game total is now  ════════  15  ════════
──────── The computer chooses  1  as it's choice.
──────── The game total is now  ════════  16  ════════

──────── Please enter a number from  1 ───► 3               (or Quit):
1                                                                          ◄■■■■■■■■■■ user input
──────── The game total is now  ════════  17  ════════
──────── The computer chooses  1  as it's choice.
──────── The game total is now  ════════  18  ════════

──────── Please enter a number from  1 ───► 3               (or Quit):
3                                                                          ◄■■■■■■■■■■ user input
──────── The game total is now  ════════  21  ════════

──────── Congratulations!   You have won the  21  game.
```

## Ring

` # Project : 21 Game load "guilib.ring" limit = 21posold = 0button = list(limit)mynum = list(3)yournum = list(3) new qapp         {        win1 = new qwidget() {                  setwindowtitle("21 Game")                  setgeometry(100,100,1000,600)                  label1 = new qlabel(win1) {                              setgeometry(10,10,1000,600)                              settext("")                  }                   label2 = new qlabel(win1) {                              setgeometry(240,50,120,40)                              setAlignment(Qt_AlignHCenter)                              setFont(new qFont("Verdana",12,100,0))                              settext("my number:")                  }                   label3 = new qlabel(win1) {                              setgeometry(640,50,120,40)                              setAlignment(Qt_AlignHCenter)                              setFont(new qFont("Verdana",12,100,0))                              settext("your number:")                  }                   for p = 1 to 3                       mynum[p] = new qpushbutton(win1) {                                          setgeometry(200+p*40,100,40,40)                                          setstylesheet("background-color:orange")                                          settext(string(p))                                          setclickevent("choose(" + string(p) + ",1)")                                          }                   next                    for p = 1 to 3                        yournum[p] = new qpushbutton(win1) {                                             setgeometry(600+p*40,100,40,40)                                             setstylesheet("background-color:white")                                             settext(string(p))                                             setclickevent("choose(" + string(p) + ",2)")                                             }                   next                    for n = 1 to limit                        button[n] = new qpushbutton(win1) {                                          setgeometry(40+n*40,190,40,40)                                          settext(string(n))                                          }                    next                    show()        }        exec()        } func choose(ch,ym)        pos = posold + ch        if pos > limit           msg = "You must choose number from 1 to " + string(limit - posold)           msgBox(msg)           for n = 1 to 3                mynum[n].setenabled(false)                yournum[n].setenabled(false)           next           return        ok        for n = posold+1 to pos             if ym = 1                button[n] { setstylesheet("background-color:orange") }             else                button[n] { setstylesheet("background-color:white") }             ok        next        posold = pos        if ym = 1           for n = 1 to 3                mynum[n].setenabled(false)                yournum[n].setenabled(true)           next         else           for n = 1 to 3                mynum[n].setenabled(true)                yournum[n].setenabled(false)           next         ok         if pos = 21            if ym = 1               msgBox("I won!")            else               msgBox("You won!")            ok         ok func msgBox(text) {	m = new qMessageBox(win1) {	       setWindowTitle("21 Game")	       setText(text)	       show()	       }        } `

Output:
21 Game