Middle three digits

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Task
Middle three digits
You are encouraged to solve this task according to the task description, using any language you may know.
Task

Write a function/procedure/subroutine that is called with an integer value and returns the middle three digits of the integer if possible or a clear indication of an error if this is not possible.

Note: The order of the middle digits should be preserved.

Your function should be tested with the following values; the first line should return valid answers, those of the second line should return clear indications of an error:

123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345
1, 2, -1, -10, 2002, -2002, 0

Show your output on this page.

11l

Translation of: Python

<lang 11l>F middle_three_digits(i)

  V s = String(abs(i))
  assert(s.len >= 3 & s.len % 2 == 1, ‘Need odd and >= 3 digits’)
  R s[s.len I/ 2 - 1 .+ 3]

V passing = [123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345] V failing = [1, 2, -1, -10, 2002, -2002, 0] L(x) passing [+] failing

  X.try
     V answer = middle_three_digits(x)
     print(‘middle_three_digits(#.) returned: #.’.format(x, answer))
  X.catch AssertionError error
     print(‘middle_three_digits(#.) returned error: ’.format(x)‘’String(error))</lang>
Output:
middle_three_digits(123) returned: 123
middle_three_digits(12345) returned: 234
middle_three_digits(1234567) returned: 345
middle_three_digits(987654321) returned: 654
middle_three_digits(10001) returned: 000
middle_three_digits(-10001) returned: 000
middle_three_digits(-123) returned: 123
middle_three_digits(-100) returned: 100
middle_three_digits(100) returned: 100
middle_three_digits(-12345) returned: 234
middle_three_digits(1) returned error: Need odd and >= 3 digits
middle_three_digits(2) returned error: Need odd and >= 3 digits
middle_three_digits(-1) returned error: Need odd and >= 3 digits
middle_three_digits(-10) returned error: Need odd and >= 3 digits
middle_three_digits(2002) returned error: Need odd and >= 3 digits
middle_three_digits(-2002) returned error: Need odd and >= 3 digits
middle_three_digits(0) returned error: Need odd and >= 3 digits

Ada

<lang Ada>with Ada.Text_IO;

procedure Middle_Three_Digits is

  Impossible: exception;
  function Middle_String(I: Integer; Middle_Size: Positive) return String is
     S: constant String := Integer'Image(I);
     First: Natural := S'First;
     Full_Size, Border: Natural;
  begin
     while S(First) not in '0' .. '9' loop -- skip leading blanks and minus
        First := First + 1;
     end loop;
     Full_Size := S'Last-First+1;
     if (Full_Size < Middle_Size) or (Full_Size mod 2 = 0) then
        raise Impossible;
     else
        Border := (Full_Size - Middle_Size)/2;
        return S(First+Border .. First+Border+Middle_Size-1);
     end if;
  end Middle_String;
  Inputs: array(Positive range <>) of Integer :=
    (123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345,
     1, 2, -1, -10, 2002, -2002, 0);
  Error_Message: constant String := "number of digits must be >= 3 and odd";
  package IIO is new Ada.Text_IO.Integer_IO(Integer);

begin

  for I in Inputs'Range loop
     IIO.Put(Inputs(I), Width => 9);
     Ada.Text_IO.Put(": ");
     begin
        Ada.Text_IO.Put(Middle_String(Inputs(I), 3));
     exception
        when Impossible => Ada.Text_IO.Put("****" & Error_Message & "****");
     end;
     Ada.Text_IO.New_Line;
  end loop;

end Middle_Three_Digits;</lang>

Output:
      123: 123
    12345: 234
  1234567: 345
987654321: 654
    10001: 000
   -10001: 000
     -123: 123
     -100: 100
      100: 100
   -12345: 234
        1: ****number of digits must be >= 3 and odd****
        2: ****number of digits must be >= 3 and odd****
       -1: ****number of digits must be >= 3 and odd****
      -10: ****number of digits must be >= 3 and odd****
     2002: ****number of digits must be >= 3 and odd****
    -2002: ****number of digits must be >= 3 and odd****
        0: ****number of digits must be >= 3 and odd****

Aime

<lang aime>void m3(integer i) {

   text s;
   s = itoa(i);
   if (s[0] == '-') {
       s = delete(s, 0);
   }
   if (~s < 3) {
       v_integer(i);
       v_text(" has not enough digits\n");
   } elif (~s & 1) {
       o_form("/w9/: ~\n", i, cut(s, ~s - 3 >> 1, 3));
   } else {
       v_integer(i);
       v_text(" has an even number of digits\n");
   }

}

void middle_3(...) {

   integer i;
   i = 0;
   while (i < count()) {
       m3($i);
       i += 1;
   }

}

integer main(void) {

   middle_3(123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100,
            -12345, 1, 2, -1, -10, 2002, -2002, 0);
   return 0;

}</lang>

Output:
      123: 123
    12345: 234
  1234567: 345
987654321: 654
    10001: 000
   -10001: 000
     -123: 123
     -100: 100
      100: 100
   -12345: 234
1 has not enough digits
2 has not enough digits
-1 has not enough digits
-10 has not enough digits
2002 has an even number of digits
-2002 has an even number of digits
0 has not enough digits

ALGOL 68

Works with: ALGOL 68G version Any - tested with release 2.6.win32

<lang algol68># we define a UNION MODE so that our middle 3 digits PROC can #

  1. return either an integer on success or a error message if #
  2. the middle 3 digits couldn't be extracted #

MODE EINT = UNION( INT # success value #, STRING # error message # );

  1. PROC to return the middle 3 digits of an integer. #
  2. if this is not possible, an error message is returned #
  3. instead #

PROC middle 3 digits = ( INT number ) EINT: BEGIN

   # convert the absolute value of the number to a string with the  #
   # minumum possible number characters                             #
   STRING digits     = whole( ABS number, 0 );
   INT    len        = UPB digits;
   IF   len < 3
   THEN
       # number has less than 3 digits #
       # return an error message       #
       "number must have at least three digits"
   ELIF ( len MOD 2 ) = 0
   THEN
       # the number has an even number of digits #
       # return an error message                 #
       "number must have an odd number of digits"
   ELSE
       # the number is suitable for extraction of the middle 3 digits #
       INT first digit pos = 1 + ( ( len - 3 ) OVER 2 );
       # the result is the integer value of the three digits          #
       ( ( ( ABS digits[ first digit pos     ] - ABS "0" ) * 100 )
       + ( ( ABS digits[ first digit pos + 1 ] - ABS "0" ) *  10 )
       + ( ( ABS digits[ first digit pos + 2 ] - ABS "0" )       )
       )
   FI

END; # middle 3 digits #

main: (

   # test the middle 3 digits PROC #
   []INT test values = (    123,  12345, 1234567, 987654321
                       ,  10001, -10001,    -123,      -100
                       ,    100, -12345
                         # the following values should fail #
                       , 1, 2, -1, -10, 2002, -2002, 0
                       );
   FOR test number FROM LWB test values TO UPB test values
   DO
       CASE middle 3 digits( test values[ test number ] )
       IN
       ( INT     success value ):    # got the middle 3 digits #
           printf( ( $ 11z-d, " : ", 3d $
                   , test values[ test number ]
                   , success value
                   )
                 )
           ,
       ( STRING  error message  ):    # got an error message   #
           printf( ( $ 11z-d, " : ", n( UPB error message )a $
                   , test values[ test number ]
                   , error message
                   )
                 )
       ESAC;
       print( ( newline ) )
   OD

)</lang>

Output:
          123 : 123
        12345 : 234
      1234567 : 345
    987654321 : 654
        10001 : 000
       -10001 : 000
         -123 : 123
         -100 : 100
          100 : 100
       -12345 : 234
            1 : number must have at least three digits
            2 : number must have at least three digits
           -1 : number must have at least three digits
          -10 : number must have at least three digits
         2002 : number must have an odd number of digits
        -2002 : number must have an odd number of digits
            0 : number must have at least three digits

ALGOL W

<lang algolw>begin

   % record structure that will be used to return the middle 3 digits of a number   %
   % if the middle three digits can't be determined, isOk will be false and message %
   % will contain an error message                                                  %
   % if the middle 3 digts can be determined, middle3 will contain the middle 3     %
   % digits and isOk will be true                                                   %
   record MiddleThreeDigits ( integer middle3; logical isOk; string(80) message );
   % finds the middle3 digits of a number or describes why they can't be found      %
   reference(MiddleThreeDigits) procedure findMiddleThreeDigits ( integer value number ) ;
       begin
           integer n, digitCount, d;
           n          := abs( number );
           % count the number of digits the number has %
           digitCount := if n = 0 then 1 else 0;
           d          := n;
           while d > 0 do begin
               digitCount := digitCount + 1;
               d          := d div 10
           end while_d_gt_0 ;
           if      digitCount < 3        then MiddleThreeDigits( 0, false, "Number must have at least 3 digits"       )
           else if not odd( digitCount ) then MiddleThreeDigits( 0, false, "Number must have an odd number of digits" )
           else begin
               % can find the middle three digits %
               integer m3;
               m3 := n;
               for d := 1 until ( digitCount - 3 ) div 2 do m3 := m3 div 10;
               MiddleThreeDigits( m3 rem 1000, true, "" )
           end
       end findMiddleThreeDigits ;
   % test the findMiddleThreeDigits procedure %
   for n := 123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0 do begin
       reference(MiddleThreeDigits) m3;
       i_w := 10; s_w := 0; % set output formating %
       m3 := findMiddleThreeDigits( n );
       write( n, ": " );
       if not isOk(m3) then writeon( message(m3) )
       else begin
           % as we return the middle three digits as an integer, we must manually 0 pad %
           if middle3(m3) < 100 then writeon( "0" );
           if middle3(m3) <  10 then writeon( "0" );
           writeon( i_w := 1, middle3(m3) )
       end
   end for_n

end.</lang>

Output:
       123: 123
     12345: 234
   1234567: 345
 987654321: 654
     10001: 000
    -10001: 000
      -123: 123
      -100: 100
       100: 100
    -12345: 234
         1: Number must have at least 3 digits
         2: Number must have at least 3 digits
        -1: Number must have at least 3 digits
       -10: Number must have at least 3 digits
      2002: Number must have an odd number of digits
     -2002: Number must have an odd number of digits
         0: Number must have at least 3 digits

AppleScript

Procedural

987654321 is too large to be represented as an AppleScript integer, so "integer value" is taken here to refer to the numeric value rather than to the language class. AppleScript automatically coerces numeric text and single-item lists to appropriate number classes where necessary and possible, so these are acceptable as parameters too.

<lang applescript>on middle3Digits(n)

   try
       n as number -- Errors if n isn't a number or coercible thereto.
       set s to n as text -- Keep for the ouput string.
       if (n mod 1 is not 0) then error (s & " isn't an integer value.")
       if (n < 0) then set n to -n
       if (n < 100) then error (s & " has fewer than three digits.")
       -- Coercing large numbers to text may result in E notation, so extract the digit values individually.
       set theDigits to {}
       repeat until (n = 0)
           set beginning of theDigits to n mod 10 as integer
           set n to n div 10
       end repeat
       set c to (count theDigits)
       if (c mod 2 is 0) then error (s & " has an even number of digits.")
   on error errMsg
       return "middle3Digits handler got an error: " & errMsg
   end try
   set i to (c - 3) div 2 + 1
   set {x, y, z} to items i thru (i + 2) of theDigits
   
   return "The middle three digits of " & s & " are " & ((x as text) & y & z & ".")

end middle3Digits

-- Test code: set testNumbers to {123, 12345, 1234567, "987654321", "987654321" as number, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0} set output to {} repeat with thisNumber in testNumbers

   set end of output to middle3Digits(thisNumber)

end repeat set astid to AppleScript's text item delimiters set AppleScript's text item delimiters to linefeed set output to output as text set AppleScript's text item delimiters to astid return output</lang>

Output:

<lang applescript>"The middle three digits of 123 are 123. The middle three digits of 12345 are 234. The middle three digits of 1234567 are 345. The middle three digits of 987654321 are 654. The middle three digits of 9.87654321E+8 are 654. The middle three digits of 10001 are 000. The middle three digits of -10001 are 000. The middle three digits of -123 are 123. The middle three digits of -100 are 100. The middle three digits of 100 are 100. The middle three digits of -12345 are 234. middle3Digits handler got an error: 1 has fewer than three digits. middle3Digits handler got an error: 2 has fewer than three digits. middle3Digits handler got an error: -1 has fewer than three digits. middle3Digits handler got an error: -10 has fewer than three digits. middle3Digits handler got an error: 2002 has an even number of digits. middle3Digits handler got an error: -2002 has an even number of digits. middle3Digits handler got an error: 0 has fewer than three digits."</lang>

Functional

<lang applescript>-------------------- MID THREE DIGITS ---------------------

-- mid3digits :: Int -> Either String String on mid3digits(n)

   -- Either a message explaining why
   -- no "mid 3 digits" are defined for n,
   -- or the mid 3 digits themselves.
   
   set m to abs(n)
   if 100 > m then
       |Left|("Less than 3 digits")
       
   else if maxBound(1) < m then
       |Left|("Out of AppleScript integer range")
       
   else
       set s to m as string
       set intDigits to length of s
       
       if even(intDigits) then
           |Left|("Even digit count")
       else
           |Right|((items 1 thru 3 of ¬
               items (1 + ((intDigits - 3) div 2)) thru -1 of s) as string)
       end if
   end if

end mid3digits



TEST ---------------------------

on run

   set ints to map(readInt, splitOn(", ", ¬
       "123, 12345, 1234567, 987654321, 10001, -10001, " & ¬
       "-123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0"))
   
   
   script showResult
       on |λ|(x)
           either(my bracketed, my str, x)
       end |λ|
   end script
   
   fTable("Mid three digits:", str, showResult, mid3digits, ints)

end run



GENERICS -------------------------

-- Left :: a -> Either a b on |Left|(x)

   {type:"Either", |Left|:x, |Right|:missing value}

end |Left|


-- Right :: b -> Either a b on |Right|(x)

   {type:"Either", |Left|:missing value, |Right|:x}

end |Right|


-- abs :: Num -> Num on abs(x)

   -- Absolute value.
   if 0 > x then
       -x
   else
       x
   end if

end abs


-- even :: Int -> Bool on even(x)

   0 = x mod 2

end even


-- maxBound :: a -> a on maxBound(x)

   set c to class of x
   if text is c then
       character id 65535
   else if integer is c then
       (2 ^ 29 - 1)
   else if real is c then
       1.797693E+308
   else if boolean is c then
       true
   end if

end maxBound



GENERICS FOR TEST AND DISPLAY ---------------------

-- bracketed :: String -> String on bracketed(s)

   "(" & s & ")"

end bracketed


-- compose (<<<) :: (b -> c) -> (a -> b) -> a -> c on compose(f, g)

   script
       property mf : mReturn(f)
       property mg : mReturn(g)
       on |λ|(x)
           mf's |λ|(mg's |λ|(x))
       end |λ|
   end script

end compose


-- either :: (a -> c) -> (b -> c) -> Either a b -> c on either(lf, rf, e)

   if missing value is |Left| of e then
       tell mReturn(rf) to |λ|(|Right| of e)
   else
       tell mReturn(lf) to |λ|(|Left| of e)
   end if

end either


-- foldl :: (a -> b -> a) -> a -> [b] -> a on foldl(f, startValue, xs)

   tell mReturn(f)
       set v to startValue
       set lng to length of xs
       repeat with i from 1 to lng
           set v to |λ|(v, item i of xs, i, xs)
       end repeat
       return v
   end tell

end foldl


-- fTable :: String -> (a -> String) -> (b -> String) -> (a -> b) -> [a] -> String on fTable(s, xShow, fxShow, f, xs)

   set ys to map(xShow, xs)
   set w to maximum(map(my |length|, ys))
   script arrowed
       on |λ|(a, b)
           justifyRight(w, space, a) & " -> " & b
       end |λ|
   end script
   s & linefeed & unlines(zipWith(arrowed, ¬
       ys, map(compose(fxShow, f), xs)))

end fTable


-- justifyRight :: Int -> Char -> String -> String on justifyRight(n, cFiller, strText)

   if n > length of strText then
       text -n thru -1 of ((replicate(n, cFiller) as text) & strText)
   else
       strText
   end if

end justifyRight


-- length :: [a] -> Int on |length|(xs)

   set c to class of xs
   if list is c or string is c then
       length of xs
   else
       (2 ^ 29 - 1) -- (maxInt - simple proxy for non-finite)
   end if

end |length|


-- map :: (a -> b) -> [a] -> [b] on map(f, xs)

   -- The list obtained by applying f
   -- to each element of xs.
   tell mReturn(f)
       set lng to length of xs
       set lst to {}
       repeat with i from 1 to lng
           set end of lst to |λ|(item i of xs, i, xs)
       end repeat
       return lst
   end tell

end map


-- maximum :: Ord a => [a] -> a on maximum(xs)

   script
       on |λ|(a, b)
           if a is missing value or b > a then
               b
           else
               a
           end if
       end |λ|
   end script
   
   foldl(result, missing value, xs)

end maximum


-- min :: Ord a => a -> a -> a on min(x, y)

   if y < x then
       y
   else
       x
   end if

end min


-- mReturn :: First-class m => (a -> b) -> m (a -> b) on mReturn(f)

   -- 2nd class handler function lifted into 1st class script wrapper. 
   if script is class of f then
       f
   else
       script
           property |λ| : f
       end script
   end if

end mReturn


-- readInt :: String -> Int on readInt(s)

   s as integer

end readInt


-- Egyptian multiplication - progressively doubling a list, appending -- stages of doubling to an accumulator where needed for binary -- assembly of a target length -- replicate :: Int -> a -> [a] on replicate(n, a)

   set out to {}
   if 1 > n then return out
   set dbl to {a}
   
   repeat while (1 < n)
       if 0 < (n mod 2) then set out to out & dbl
       set n to (n div 2)
       set dbl to (dbl & dbl)
   end repeat
   return out & dbl

end replicate


-- splitOn :: String -> String -> [String] on splitOn(pat, src)

   set {dlm, my text item delimiters} to ¬
       {my text item delimiters, pat}
   set xs to text items of src
   set my text item delimiters to dlm
   return xs

end splitOn


-- str :: a -> String on str(x)

   x as string

end str


-- unlines :: [String] -> String on unlines(xs)

   -- A single string formed by the intercalation
   -- of a list of strings with the newline character.
   set {dlm, my text item delimiters} to ¬
       {my text item delimiters, linefeed}
   set s to xs as text
   set my text item delimiters to dlm
   s

end unlines


-- zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] on zipWith(f, xs, ys)

   set lng to min(length of xs, length of ys)
   set lst to {}
   if 1 > lng then
       return {}
   else
       tell mReturn(f)
           repeat with i from 1 to lng
               set end of lst to |λ|(item i of xs, item i of ys)
           end repeat
           return lst
       end tell
   end if

end zipWith</lang>

Output:
Mid three digits:
          123 -> 123
        12345 -> 234
      1234567 -> 345
9.87654321E+8 -> (Out of AppleScript integer range)
        10001 -> 000
       -10001 -> 000
         -123 -> 123
         -100 -> 100
          100 -> 100
       -12345 -> 234
            1 -> (Less than 3 digits)
            2 -> (Less than 3 digits)
           -1 -> (Less than 3 digits)
          -10 -> (Less than 3 digits)
         2002 -> (Even digit count)
        -2002 -> (Even digit count)
            0 -> (Less than 3 digits)

ATS

<lang ATS> (* ****** ****** *) //

  1. include

"share/atspre_staload.hats"

  1. include

"share/HATS/atspre_staload_libats_ML.hats" // (* ****** ****** *) // extern fun int2digits(x: int): list0(int) // (* ****** ****** *)

implement int2digits(x) = loop(x, list0_nil) where { // fun loop (

x: int, res: list0(int)

) : list0(int) =

 if x > 0 then loop(x/10, list0_cons(x%10, res)) else res

// } (* end of [int2digits] *)

(* ****** ****** *)

extern fun Middle_three_digits(x: int): void

(* ****** ****** *)

implement Middle_three_digits

 (x0) = let

// val x1 = ( if x0 >= 0 then x0 else ~x0 ) : int // fun skip ( ds: list0(int), k: int ) : list0(int) =

 if k > 0 then skip(ds.tail(), k-1) else ds

// val ds =

 int2digits(x1)

// val n0 = length(ds) // in // if (n0 <= 2) then ( println! ("Middle-three-digits(", x0, "): Too small!") ) else ( if (n0 % 2 = 0) then ( println! ( "Middle-three-digits(", x0, "): Even number of digits!" ) ) else let

 val ds =
   skip(ds, (n0-3)/2)
 val-list0_cons(d1, ds) = ds
 val-list0_cons(d2, ds) = ds
 val-list0_cons(d3, ds) = ds

in

 println! ("Middle-three-digits(", x0, "): ", d1, d2, d3) 

end // end of [else] ) // end // end of [Middle_three_digits]

(* ****** ****** *)

implement main0() = { // val thePassing = g0ofg1 ( $list{int} (

 123

, 12345 , 1234567 , 987654321 , 10001, ~10001 , ~123, ~100, 100, ~12345 ) ) val theFailing = g0ofg1($list{int}(1, 2, ~1, ~10, 2002, ~2002, 0)) // val () = thePassing.foreach()(lam x => Middle_three_digits(x)) val () = theFailing.foreach()(lam x => Middle_three_digits(x)) // } (* end of [main0] *)

(* ****** ****** *) </lang>

Output:
Middle-three-digits(123): 123
Middle-three-digits(12345): 234
Middle-three-digits(1234567): 345
Middle-three-digits(987654321): 654
Middle-three-digits(10001): 000
Middle-three-digits(-10001): 000
Middle-three-digits(-123): 123
Middle-three-digits(-100): 100
Middle-three-digits(100): 100
Middle-three-digits(-12345): 234
Middle-three-digits(1): Too small!
Middle-three-digits(2): Too small!
Middle-three-digits(-1): Too small!
Middle-three-digits(-10): Too small!
Middle-three-digits(2002): Even number of digits!
Middle-three-digits(-2002): Even number of digits!
Middle-three-digits(0): Too small!

AutoHotkey

<lang AutoHotkey>Numbers:="123,12345,1234567,987654321,10001,-10001,-123,-100,100,-12345,1,2,-1,-10,2002,-2002,0" Loop, parse, Numbers, `, { if A_LoopField is not number log := log . A_LoopField . "`t: Not a valid number`n" else if((d:=StrLen(n:=RegExReplace(A_LoopField,"\D")))<3) log := log . A_LoopField . "`t: Too short`n" else if(!Mod(d,2)) log := log . A_LoopField . "`t: Not an odd number of digits`n" else log := log . A_LoopField . "`t: " . SubStr(n,((d-3)//2)+1,3) . "`n" } MsgBox % log</lang>

Output:
123	: 123
12345	: 234
1234567	: 345
987654321	: 654
10001	: 000
-10001	: 000
-123	: 123
-100	: 100
100	: 100
-12345	: 234
1	: Too short
2	: Too short
-1	: Too short
-10	: Too short
2002	: Not an odd number of digits
-2002	: Not an odd number of digits
0	: Too short

AWK

<lang AWK>#!/bin/awk -f

  1. use as: awk -f middle_three_digits.awk

BEGIN { n = split("123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345 1 2 -1 -10 2002 -2002 0", arr)

for (i=1; i<=n; i++) { if (arr[i] !~ /^-?[0-9]+$/) { printf("%10s : invalid input: not a number\n", arr[i]) continue }

num = arr[i]<0 ? -arr[i]:arr[i] len = length(num)

if (len < 3) { printf("%10s : invalid input: too few digits\n", arr[i]) continue }

if (len % 2 == 0) { printf("%10s : invalid input: even number of digits\n", arr[i]) continue }

printf("%10s : %s\n", arr[i], substr(num, len/2, 3)) } } </lang>

Output:
       123 : 123
     12345 : 234
   1234567 : 345
 987654321 : 654
     10001 : 000
    -10001 : 000
      -123 : 123
      -100 : 100
       100 : 100
    -12345 : 234
         1 : invalid input: too few digits
         2 : invalid input: too few digits
        -1 : invalid input: too few digits
       -10 : invalid input: too few digits
      2002 : invalid input: even number of digits
     -2002 : invalid input: even number of digits
         0 : invalid input: too few digits

BASIC

Applesoft BASIC

<lang ApplesoftBasic>100 DEF FN L(N) = LEN(STR$(INT(ABS(N)))) 110 DEF FN N(N) = VAL(MID$(STR$(INT(ABS(N))),(FN L(N)-1)/2,3)) 120 DEF FN EVEN(N) = INT(N/2) = N/2 130 FOR I = 1 TO 20 140 READ N 150 PRINT N":", 160 GOSUB 100"MIDDLE THREE DIGITS 170 PRINT R$ 180 NEXT 190 END 200 R$ = "" 210 IF FN EVEN(FN L(N)) THEN R$ = "?EVEN," 220 IF FN L(N) < 3 THEN R$ = R$ + "ONLY " + STR$(FN L(N)) + " DIGIT" + MID$("S",FN L(N) - 1, 1) 230 IF RIGHT$(R$, 1) = "," THEN R$ = LEFT$(R$, LEN(R$) - 1) : RETURN 240 IF LEFT$(R$, 1) = "?" THEN RETURN 250 IF R$ <> "" THEN R$ = "?" + R$ : RETURN 260 R$ = STR$(FN N(N)) 270 IF LEN(R$) = 1 THEN R$ = "00" + R$ 280 IF LEN(R$) = 2 THEN R$ = "0" + R$ 290 RETURN 300 DATA123,12345,1234567,987654321,10001,-10001,-123,-100,100,-12345 310 DATA1,2,-1,-10,2002,-2002,0 </lang>

Output:
123:            123
12345:          234
1234567:        345
987654321:      654
10001:          000
-10001:         000
-123:           123
-100:           100
100:            100
-12345:         234
1:              ?ONLY 1 DIGIT
2:              ?ONLY 1 DIGIT
-1:             ?ONLY 1 DIGIT
-10:            ?EVEN,ONLY 2 DIGITS
2002:           ?EVEN
-2002:          ?EVEN
0:              ?ONLY 1 DIGIT

BBC BASIC

<lang bbcbasic>REM >midthree FOR i% = 1 TO 17

 READ test%
 PRINT test%; " -> "; FN_middle_three(test%)

NEXT END

DATA 123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345 DATA 1, 2, -1, -10, 2002, -2002, 0

DEF FN_middle_three(n%) LOCAL n$ n$ = STR$ ABS n% CASE TRUE OF WHEN LEN n$ < 3

 = "Not enough digits"

WHEN LEN n$ MOD 2 = 0

 = "Even number of digits"

OTHERWISE

 = MID$(n$, LEN n$ / 2, 3)

ENDCASE</lang>

Output:
       123 -> 123
     12345 -> 234
   1234567 -> 345
 987654321 -> 654
     10001 -> 000
    -10001 -> 000
      -123 -> 123
      -100 -> 100
       100 -> 100
    -12345 -> 234
         1 -> Not enough digits
         2 -> Not enough digits
        -1 -> Not enough digits
       -10 -> Not enough digits
      2002 -> Even number of digits
     -2002 -> Even number of digits
         0 -> Not enough digits

FBSL

<lang qbasic>#APPTYPE CONSOLE

DIM numbers AS STRING = "123,12345,1234567,987654321,10001,-10001,-123,-100,100,-12345,1,2,-1,-10,2002,-2002,0" DIM dict[] = Split(numbers, ",") DIM num AS INTEGER DIM num2 AS INTEGER DIM powered AS INTEGER

FOR DIM i = 0 TO COUNT(dict) - 1

   num2 = dict[i]
   num = ABS(num2)
   IF num < 100 THEN
       display(num2, "is too small")
   ELSE
       FOR DIM j = 9 DOWNTO 1
           powered = 10 ^ j
           IF num >= powered THEN
               IF j MOD 2 = 1 THEN
                   display(num2, "has even number of digits")
               ELSE
                   display(num2, middle3(num, j))
               END IF
               EXIT FOR
           END IF
       NEXT
   END IF

NEXT

PAUSE

FUNCTION display(num, msg)

   PRINT LPAD(num, 11, " "), " --> ", msg

END FUNCTION

FUNCTION middle3(n, pwr)

   DIM power AS INTEGER = (pwr \ 2) - 1
   DIM m AS INTEGER = n
   m = m \ (10 ^ power)
   m = m MOD 1000
   IF m = 0 THEN
       RETURN "000"
   ELSE
       RETURN m
   END IF

END FUNCTION</lang> Output

        123 --> 123
      12345 --> 234
    1234567 --> 345
  987654321 --> 654
      10001 --> 000
     -10001 --> 000
       -123 --> 123
       -100 --> 100
        100 --> 100
     -12345 --> 234
          1 --> is too small
          2 --> is too small
         -1 --> is too small
        -10 --> is too small
       2002 --> has even number of digits
      -2002 --> has even number of digits
          0 --> is too small

Press any key to continue...

IS-BASIC

<lang IS-BASIC>100 INPUT PROMPT "Number: ":N 120 PRINT MIDDLE$(N) 130 DEF MIDDLE$(N) 140 LET N$=STR$(ABS(N)) 150 IF LEN(N$)<3 THEN LET MIDDLE$="Not enough digits":EXIT DEF 160 IF MOD(LEN(N$),2)=0 THEN LET MIDDLE$="Even number of digits":EXIT DEF 170 LET P=(LEN(N$)-3)/2 180 LET MIDDLE$=N$(P+1:P+3) 190 END DEF</lang>


PureBasic

<lang purebasic>Procedure.s middleThreeDigits(x.q)

 Protected x$, digitCount
 If x < 0: x = -x: EndIf
 x$ = Str(x)
 digitCount = Len(x$)
 If digitCount < 3
   ProcedureReturn "invalid input: too few digits"
 ElseIf digitCount % 2 = 0
   ProcedureReturn "invalid input: even number of digits"
 EndIf
 ProcedureReturn Mid(x$,digitCount / 2, 3)

EndProcedure

If OpenConsole()

 Define testValues$ = "123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345 1 2 -1 -10 2002 -2002 0"
 
 Define i, value.q, numTests = CountString(testValues$, " ") + 1
 For i = 1 To numTests
   value = Val(StringField(testValues$, i, " "))
   PrintN(RSet(Str(value), 12, " ") + " : " + middleThreeDigits(value))
 Next
 
 Print(#crlf$ + #crlf$ + "Press ENTER to exit"): Input()
 CloseConsole()

EndIf</lang> Sample output:

         123 : 123
       12345 : 234
     1234567 : 345
   987654321 : 654
       10001 : 000
      -10001 : 000
        -123 : 123
        -100 : 100
         100 : 100
      -12345 : 234
           1 : invalid input: too few digits
           2 : invalid input: too few digits
          -1 : invalid input: too few digits
         -10 : invalid input: too few digits
        2002 : invalid input: even number of digits
       -2002 : invalid input: even number of digits
           0 : invalid input: too few digits

Run BASIC

<lang runbasic>x$ = "123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0"

while word$(x$,i+1,",") <> ""

i	= i + 1
a1$	= trim$(word$(x$,i,","))
if left$(a1$,1) = "-" then a$ = mid$(a1$,2) else a$ = a1$
if (len(a$) and 1) = 0 or len(a$) < 3 then 
  print a1$;chr$(9);" length < 3 or is even"
 else
  print mid$(a$,((len(a$)-3)/2)+1,3);" ";a1$
end if

wend end</lang>

123 123
234 12345
345 1234567
654 987654321
000 10001
000 -10001
123 -123
100 -100
100 100
234 -12345
1	 length < 3 or is even
2	 length < 3 or is even
-1	 length < 3 or is even
-10	 length < 3 or is even
2002	 length < 3 or is even
-2002	 length < 3 or is even
0	 length < 3 or is even

Batch File

<lang dos>@echo off setlocal enabledelayedexpansion

%== Initialization ==% set "numbers=123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0"

%== The Main Thing ==% for %%N in (%numbers%) do ( call :middle3 %%N ) echo. pause exit /b 0 %==/The Main Thing ==%

%== The Procedure ==%

middle3

set str=%1 %== Making sure that str is positive ==% if !str! lss 0 set /a str*=-1

%== Alternative for finding the string length ==% %== But this has a limit of 1000 characters ==% set leng=0&if not "!str!"=="" for /l %%. in (0,1,1000) do if not "!str:~%%.,1!"=="" set /a leng+=1

if !leng! lss 3 ( echo.%~1: [ERROR] Input too small. goto :EOF )

set /a "test2=leng %% 2,trimmer=(leng - 3) / 2"

if !test2! equ 0 ( echo.%~1: [ERROR] Even number of digits. goto :EOF )

%== Passed the tests. Now, really find the middle 3 digits... ==% if !trimmer! equ 0 ( echo.%~1: !str! ) else ( echo.%~1: !str:~%trimmer%,-%trimmer%! ) goto :EOF %==/The Procedure ==%</lang>

Output:
123:            123
12345:          234
1234567:                345
987654321:              654
10001:          000
-10001:         000
-123:           123
-100:           100
100:            100
-12345:         234
1:              [ERROR] Input too small.
2:              [ERROR] Input too small.
-1:             [ERROR] Input too small.
-10:            [ERROR] Input too small.
2002:           [ERROR] Even number of digits.
-2002:          [ERROR] Even number of digits.
0:              [ERROR] Input too small.

Press any key to continue . . .

Befunge

Reads the integer value from stdin and writes the middle three digits (or an error message) to stdout.

<lang befunge>>&>:0`2*1-*0>v v+*86%+55:p00< >\55+/:00g1+\| v3_v#*%2\`2::< ->@>0".rorrE"v 2^,+55_,#!>#:< >/>\#<$#-:#1_v >_@#<,+55,,,$<</lang>

Output:
(multiple runs)
123
123
12345
234
1234567
345
987654321
654
10001
000
-10001
000
-123
123
-100
100
100
100
-12345
234
1
Error.
2
Error.
-1
Error.
-10
Error.
2002
Error.
-2002
Error.
0
Error.

Bracmat

<lang bracmat>( ( middle3

 =   x p
   .     @(!arg:? [?p:? [(1/2*!p+-3/2) %?x [(1/2*!p+3/2) ?)
       & !x
     |   !arg
         ( !p:<3&"is too small"
         | "has even number of digits"
         )
 )

& 123 12345 1234567 987654321 10001 -10001 -123 -100 100

     -12345 1 2 -1 -10 2002 -2002 0
 : ?L

& whl'(!L:%?e ?L&out$(middle3$!e)) & ); </lang> Output:

123
234
345
654
000
000
123
100
100
234
1 is too small
2 is too small
-1 is too small
-10 is too small
2002 has even number of digits
-2002 has even number of digits
0 is too small

Burlesque

<lang blsq> blsq ) {123 12345 1234567 987654321 -10001 -123}{XX{~-}{L[3.>}w!m]\[}m[uN 123 234 345 654 000 123 </lang>

m]\[ and uN are just for displaying it nicely.

C

This code is followed by its output. <lang c>

  1. include <stdio.h>
  2. include <stdlib.h>
  3. include <string.h>

// we return a static buffer; caller wants it, caller copies it char * mid3(int n) { static char buf[32]; int l; sprintf(buf, "%d", n > 0 ? n : -n); l = strlen(buf); if (l < 3 || !(l & 1)) return 0; l = l / 2 - 1; buf[l + 3] = 0; return buf + l; }

int main(void) { int x[] = {123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0, 1234567890};

int i; char *m; for (i = 0; i < sizeof(x)/sizeof(x[0]); i++) { if (!(m = mid3(x[i]))) m = "error"; printf("%d: %s\n", x[i], m); } return 0; }</lang>

123: 123
12345: 234
1234567: 345
987654321: 654
10001: 000
-10001: 000
-123: 123
-100: 100
100: 100
-12345: 234
1: error
2: error
-1: error
-10: error
2002: error
-2002: error
0: error
1234567890: error

Alternative Version

This code has been extensively rewritten. The original was purely interactive and had to be invoked each time from the console. It also did not produce the correct answer. <lang c>

  1. include <stdio.h>
  2. include <stdlib.h>
  3. include <string.h>

void midThree(char arg[]) {

   char output[4];
   int midPoint;
   arg[0]=='-'?midPoint = ((strlen(arg) + 1) / 2):midPoint = ((strlen(arg) + 1) / 2) - 1;
   
   if(strlen(arg) < 3)
       {
           printf("Error, %d is too short.\n",atoi(arg));
           return ;
       }
       else if(strlen(arg)  == 4 || strlen(arg) == 3)
       {
           printf("Error, %d has %d digits, no 3 middle digits.\n",atoi(arg),arg[0]=='-'?strlen(arg)-1:strlen(arg));
           return ;
       }
   else{
   for(int i=0; i<3; i++)
   {
       output[i] = arg[(midPoint-1) + i];
   }
   output[3] = '\0';
   printf("The middle three digits of %s are %s.\n",arg,output);

}}

int main(int argc, char * argv[]) {

   char input[50];
   int x[] = {123, 12345, 1234567, 987654321, 10001, -10001,

-123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0, 1234567890},i;

   if(argc < 2)
   {
       printf("Usage: %s <integer>\n",argv[0]);
       printf("Examples with preloaded data shown below :\n");
       
       for(i=0;i<18;i++)
       {

midThree(itoa(x[i],argv[0],10)); }

       return 1;
   }
   else
   {
       sprintf(input,"%d",atoi(argv[1]));
           midThree(argv[1]);
           return 0;
       

   }

}</lang>

Output:
Usage: C:\TurboC++\Disk\TurboC3\BIN\rosmid3_2.exe <integer>
Examples with preloaded data shown below :
Error, 123 has 3 digits, no 3 middle digits.
The middle three digits of 12345 are 234.
The middle three digits of 1234567 are 345.
The middle three digits of 987654321 are 654.
The middle three digits of 10001 are 000.
The middle three digits of -10001 are 000.
Error, -123 has 3 digits, no 3 middle digits.
Error, -100 has 3 digits, no 3 middle digits.
Error, 100 has 3 digits, no 3 middle digits.
The middle three digits of -12345 are 234.
Error, 1 is too short.
Error, 2 is too short.
Error, -1 is too short.
Error, -10 has 2 digits, no 3 middle digits.
Error, 2002 has 4 digits, no 3 middle digits.
Error, -2002 has 4 digits, no 3 middle digits.
Error, 0 is too short.
The middle three digits of 1234567890 are 456.

C++

<lang cpp>#include <iostream>

std::string middleThreeDigits(int n) {

   auto number = std::to_string(std::abs(n));
   auto length = number.size();
   if (length < 3) {
       return "less than three digits";
   } else if (length % 2 == 0) {
       return "even number of digits";
   } else {
       return number.substr(length / 2 - 1, 3);
   }

}

int main() {

   auto values {123, 12345, 1234567, 987654321, 10001,
                -10001, -123, -100, 100, -12345,
                1, 2, -1, -10, 2002, -2002, 0};
   for (auto&& v : values) {
       std::cout << "middleThreeDigits(" << v << "): " <<
                    middleThreeDigits(v) << "\n";
   }

} </lang>

Output:
middleThreeDigits(123): 123
middleThreeDigits(12345): 234
middleThreeDigits(1234567): 345
middleThreeDigits(987654321): 654
middleThreeDigits(10001): 000
middleThreeDigits(-10001): 000
middleThreeDigits(-123): 123
middleThreeDigits(-100): 100
middleThreeDigits(100): 100
middleThreeDigits(-12345): 234
middleThreeDigits(1): less than three digits
middleThreeDigits(2): less than three digits
middleThreeDigits(-1): less than three digits
middleThreeDigits(-10): less than three digits
middleThreeDigits(2002): even number of digits
middleThreeDigits(-2002): even number of digits
middleThreeDigits(0): less than three digits

C_sharp

<lang csharp>using System;

namespace RosettaCode {

   class Program
   {
       static void Main(string[] args)
       {
           string text = Math.Abs(int.Parse(Console.ReadLine())).ToString();
           Console.WriteLine(text.Length < 2 || text.Length % 2 == 0 ? "Error" : text.Substring((text.Length - 3) / 2, 3));
       }
   }

}</lang>

Output:
123:123
12345:234
1234567:345
987654321:654
10001:000
-10001:000
-123:123
-100:100
100:100
-12345:234

1:Error
2:Error
-1:Error
-10:Error
2002:Error
-2002:Error
0:Error

Clojure

<lang Clojure> (defn middle3 [v]

 (let [no (Math/abs v)
       digits (str no)
       len (count digits)]
   (cond
     (< len 3) :too_short
     (even? len) :no_middle_in_even_no_of_digits
     :else (let [mid (/ len 2)
                 start (- mid 2)]
             (apply str
                    (take 3
                          (nthnext digits start)))))))

(def passes '(123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345)) (def fails '(1 2 -1 -10 2002 -2002 0))

</lang>

Output:
user=> (map middle3 passes)
("123" "234" "345" "654" "000" "000" "123" "100" "100" "234")
user=> (map middle3 fails)
(:too_short :too_short :too_short :too_short :no_middle_in_even_no_of_digits :no_middle_in_even_no_of_digits :too_short)

COBOL

<lang COBOL>identification division. program-id. middle3. environment division. data division. working-storage section. 01 num pic 9(9).

   88 num-too-small    values are -99 thru 99.

01 num-disp pic ---------9.

01 div pic 9(9). 01 mod pic 9(9). 01 mod-disp pic 9(3).

01 digit-counter pic 999. 01 digit-div pic 9(9).

   88  no-more-digits  value 0.

01 digit-mod pic 9(9).

   88  is-even         value 0.

01 multiplier pic 9(9).

01 value-items.

   05  filler  pic s9(9) value 123.
   05  filler  pic s9(9) value 12345.
   05  filler  pic s9(9) value 1234567.
   05  filler  pic s9(9) value 987654321.
   05  filler  pic s9(9) value 10001.
   05  filler  pic s9(9) value -10001.
   05  filler  pic s9(9) value -123.
   05  filler  pic s9(9) value -100.
   05  filler  pic s9(9) value 100.
   05  filler  pic s9(9) value -12345.
   05  filler  pic s9(9) value 1.
   05  filler  pic s9(9) value 2.
   05  filler  pic s9(9) value -1.
   05  filler  pic s9(9) value -10.
   05  filler  pic s9(9) value 2002.
   05  filler  pic s9(9) value -2002.
   05  filler  pic s9(9) value 0.
   

01 value-array redefines value-items.

   05  items   pic s9(9)  occurs 17 times indexed by item.

01 result pic x(20).

procedure division. 10-main.

   perform with test after varying item from 1 by 1 until items(item) = 0
       move items(item) to num
       move items(item) to num-disp
       perform 20-check
       display num-disp " --> " result
   end-perform.
   stop run.
   

20-check.

   if num-too-small
       move "Number too small" to result
       exit paragraph
   end-if.
   perform 30-count-digits.
   divide digit-counter by 2 giving digit-div remainder digit-mod.
   if is-even
       move "Even number of digits" to result
       exit paragraph
   end-if.
   
   *> if digit-counter is 5, mul by 10
   *> if digit-counter is 7, mul by 100
   *> if digit-counter is 9, mul by 1000
       
   if digit-counter > 3
       compute multiplier rounded = 10 ** (((digit-counter - 5) / 2) + 1) 
       divide num by multiplier giving num
       divide num by 1000 giving div remainder mod
       move mod to mod-disp
   else
       move num to mod-disp
   end-if.
   move mod-disp to result.
   exit paragraph.
   

30-count-digits.

   move zeroes to digit-counter.
   move num to digit-div.
   perform with test before until no-more-digits
       divide digit-div by 10 giving digit-div remainder digit-mod
       add 1 to digit-counter
   end-perform.
   exit paragraph.</lang>

Output

       123 --> 123
     12345 --> 234
   1234567 --> 345
 987654321 --> 654
     10001 --> 000
    -10001 --> 000
      -123 --> 123
      -100 --> 100
       100 --> 100
    -12345 --> 234
         1 --> Number too small
         2 --> Number too small
        -1 --> Number too small
       -10 --> Number too small
      2002 --> Even number of digit
     -2002 --> Even number of digit
         0 --> Number too small

Optimised version <lang cobol>identification division. program-id. middle3. environment division. data division. working-storage section. 01 value-items.

       05  filler  pic s9(9) value 123.
       05  filler  pic s9(9) value 12345.
       05  filler  pic s9(9) value 1234567.
       05  filler  pic s9(9) value 987654321.
       05  filler  pic s9(9) value 10001.
       05  filler  pic s9(9) value -10001.
       05  filler  pic s9(9) value -123.
       05  filler  pic s9(9) value -100.
       05  filler  pic s9(9) value 100.
       05  filler  pic s9(9) value -12345.
       05  filler  pic s9(9) value 1.
       05  filler  pic s9(9) value 2.
       05  filler  pic s9(9) value -1.
       05  filler  pic s9(9) value -10.
       05  filler  pic s9(9) value 2002.
       05  filler  pic s9(9) value -2002.
       05  filler  pic s9(9) value 0.

01 value-array redefines value-items.

       05  items   pic s9(9)  occurs 17 times indexed by item.

01 num pic 9(9). 01 num-disp pic ---------9. 01 num2 pic 9(9).

01 power pic 9. 01 power10 pic 9(16).

01 three-digits pic 999.

01 result pic X(20).

01 flag pic 9.

   88 done value 1.

procedure division. 01-setup.

   perform 02-outer with test after varying item from 1 by 1 until items(item) = 0.
   stop run.

02-outer.

   move items(item) to num.
   move items(item) to num-disp.
   if num less than 100
       move "too small" to result
   else
       perform 03-inner with test after varying power from 9 by -1 until power = 1 or done
   end-if.
   display num-disp " --> " result.
   exit paragraph.

03-inner.

   move 0 to flag.
   compute power10 = 10 ** power.
   if num >= power10
       move 1 to flag
       if function mod(power,2) = 1
           move "even number digits" to result
       else 
           move num to num2
           compute num2 = num2 / ( 10 ** (( power / 2 ) - 1 ))
           move function mod(num2,1000) to three-digits
           move three-digits to result
       end-if
   end-if.

</lang> Output

       123 --> 123
     12345 --> 234
   1234567 --> 345
 987654321 --> 654
     10001 --> 000
    -10001 --> 000
      -123 --> 123
      -100 --> 100
       100 --> 100
    -12345 --> 234
         1 --> too small
         2 --> too small
        -1 --> too small
       -10 --> too small
      2002 --> even number digits
     -2002 --> even number digits
         0 --> too small

Common Lisp

<lang lisp> (defun mid3 (n)

 (let ((a (abs n))
       (hmd)) ; how many digits
   (labels ((give (fmt &optional x y) (return-from mid3 (format nil fmt x y)))
            (need (x) (give "Need ~a digits, not ~d." x hmd))
            (nbr (n) (give "~3,'0d" n)))
     (when (zerop n) (give "Zero is 1 digit"))
     (setq hmd (truncate (1+ (log a 10))))
     (cond ((< hmd 3) (need "3+"))
           ((= hmd 3) (nbr a))
           ((evenp hmd) (need "odd number of"))
           (t (nbr (mod (truncate a (expt 10 (/ (- hmd 3) 2))) 1000)))))))

</lang>

Test code:

<lang lisp> (loop as n in '(123 12345 1234567 987654321

                   10001 -10001 -123 -100 100 -12345
                   1 2 -1 -10 2002 -2002 0)
     do (format t "~d:~12t~a~%" n (mid3 n)))

</lang>

Output:
123:        123
12345:      234
1234567:    345
987654321:  654
10001:      000
-10001:     000
-123:       123
-100:       100
100:        100
-12345:     234
1:          Need 3+ digits, not 1.
2:          Need 3+ digits, not 1.
-1:         Need 3+ digits, not 1.
-10:        Need 3+ digits, not 2.
2002:       Need odd number of digits, not 4.
-2002:      Need odd number of digits, not 4.
0:          Zero is 1 digit

D

<lang d>import std.stdio, std.traits, std.conv;

string middleThreeDigits(T)(in T n) pure nothrow if (isIntegral!T) {

   auto s = n < 0 ? n.text[1 .. $] : n.text;
   auto len = s.length;
   if (len < 3 || len % 2 == 0)
       return "Need odd and >= 3 digits";
   auto mid = len / 2;
   return s[mid - 1 .. mid + 2];

}

void main() {

   immutable passing = [123, 12345, 1234567, 987654321, 10001, -10001,
           -123, -100, 100, -12345, long.min, long.max];
   foreach (immutable n; passing)
       writefln("middleThreeDigits(%s): %s", n, middleThreeDigits(n));
   immutable failing = [1, 2, -1, -10, 2002, -2002, 0,int.min,int.max];
   foreach (immutable n; failing)
       writefln("middleThreeDigits(%s): %s", n, middleThreeDigits(n));

}</lang>

Output:
middleThreeDigits(123): 123
middleThreeDigits(12345): 234
middleThreeDigits(1234567): 345
middleThreeDigits(987654321): 654
middleThreeDigits(10001): 000
middleThreeDigits(-10001): 000
middleThreeDigits(-123): 123
middleThreeDigits(-100): 100
middleThreeDigits(100): 100
middleThreeDigits(-12345): 234
middleThreeDigits(-9223372036854775808): 368
middleThreeDigits(9223372036854775807): 368
middleThreeDigits(1): Need odd and >= 3 digits
middleThreeDigits(2): Need odd and >= 3 digits
middleThreeDigits(-1): Need odd and >= 3 digits
middleThreeDigits(-10): Need odd and >= 3 digits
middleThreeDigits(2002): Need odd and >= 3 digits
middleThreeDigits(-2002): Need odd and >= 3 digits
middleThreeDigits(0): Need odd and >= 3 digits
middleThreeDigits(-2147483648): Need odd and >= 3 digits
middleThreeDigits(2147483647): Need odd and >= 3 digits

Alternative Version

This longer version gives a stronger typed output, and it tries to be faster avoiding conversions to string. <lang d>import std.stdio, std.traits, std.math, std.variant;

/// Returns a string with the error, or the three digits. Algebraic!(string, char[3]) middleThreeDigits(T)(in T n) if (isIntegral!T) {

   // Awkward code to face abs(T.min) when T is signed.
   ulong ln;
   static if (isSigned!T) {
       if (n >= 0) {
           ln = n;
       } else {
           if (n == T.min) {
               ln = -(n + 1);
               ln++;
           } else {
               ln = -n;
           }
       }
   } else {
       ln = n;
   }
   if (ln < 100)
       return typeof(return)("n is too short.");
   immutable uint digits = 1 + cast(uint)log10(ln);
   if (digits % 2 == 0)
       return typeof(return)("n must have an odd number of digits.");
   // From the Reddit answer by "millstone".
   int drop = (digits - 3) / 2;
   while (drop-- > 0)
       ln /= 10;
   char[3] result = void;
   result[2] = ln % 10 + '0';
   ln /= 10;
   result[1] = ln % 10 + '0';
   ln /= 10;
   result[0] = ln % 10 + '0';
   return typeof(return)(result);

}

void main() {

   immutable passing = [123, 12345, 1234567, 987654321, 10001,
                        -10001, -123, -100, 100, -12345, -8765432];
   foreach (n; passing) {
       auto mtd = middleThreeDigits(n);
       // A string result means it didn't pass.
       assert(!mtd.peek!string);
       writefln("middleThreeDigits(%d): %s", n, mtd);
   }
   writeln();
   immutable failing = [1, 2, -1, -10, 2002, -2002, 0,
                        15, int.min, int.max];
   foreach (n; failing) {
       auto mtd = middleThreeDigits(n);
       assert(mtd.peek!string);
       writefln("middleThreeDigits(%d): %s", n, mtd);
   }
   writeln();
   immutable long[] passingL = [123, 12345, 1234567, 987654321, 10001,
                                -10001, -123, -100, 100, -12345,
                                -8765432, long.min, long.max];
   foreach (n; passingL) {
       auto mtd = middleThreeDigits(n);
       assert(!mtd.peek!string);
       writefln("middleThreeDigits(%d): %s", n, mtd);
   }
   writeln();
   immutable long[] failingL = [1, 2, -1, -10, 2002, -2002, 0, 15];
   foreach (n; failingL) {
       auto mtd = middleThreeDigits(n);
       assert(mtd.peek!string);
       writefln("middleThreeDigits(%d): %s", n, mtd);
   }
   writeln();
   {
       immutable n = short.min;
       auto mtd = middleThreeDigits(n);
       assert(!mtd.peek!string);
       writefln("middleThreeDigits(cast(short)%d): %s", n, mtd);
   }

}</lang>

Output:
middleThreeDigits(123): 123
middleThreeDigits(12345): 234
middleThreeDigits(1234567): 345
middleThreeDigits(987654321): 654
middleThreeDigits(10001): 000
middleThreeDigits(-10001): 000
middleThreeDigits(-123): 123
middleThreeDigits(-100): 100
middleThreeDigits(100): 100
middleThreeDigits(-12345): 234
middleThreeDigits(-8765432): 654

middleThreeDigits(1): n is too short.
middleThreeDigits(2): n is too short.
middleThreeDigits(-1): n is too short.
middleThreeDigits(-10): n is too short.
middleThreeDigits(2002): n must have an odd number of digits.
middleThreeDigits(-2002): n must have an odd number of digits.
middleThreeDigits(0): n is too short.
middleThreeDigits(15): n is too short.
middleThreeDigits(-2147483648): n must have an odd number of digits.
middleThreeDigits(2147483647): n must have an odd number of digits.

middleThreeDigits(123): 123
middleThreeDigits(12345): 234
middleThreeDigits(1234567): 345
middleThreeDigits(987654321): 654
middleThreeDigits(10001): 000
middleThreeDigits(-10001): 000
middleThreeDigits(-123): 123
middleThreeDigits(-100): 100
middleThreeDigits(100): 100
middleThreeDigits(-12345): 234
middleThreeDigits(-8765432): 654
middleThreeDigits(-9223372036854775808): 368
middleThreeDigits(9223372036854775807): 368

middleThreeDigits(1): n is too short.
middleThreeDigits(2): n is too short.
middleThreeDigits(-1): n is too short.
middleThreeDigits(-10): n is too short.
middleThreeDigits(2002): n must have an odd number of digits.
middleThreeDigits(-2002): n must have an odd number of digits.
middleThreeDigits(0): n is too short.
middleThreeDigits(15): n is too short.

middleThreeDigits(cast(short)-32768): 276

Dart

<lang> import'dart:math';

 int length(int x)
 {
   int i,y;
 for(i=0;;i++)
 {
   y=pow(10,i);
   if(x%y==x)
     break;
 }
   return i;
 }
int middle(int x,int l)
 {
int a=(x/10)-((x%10)/10);
 int b=a%(pow(10,l-2));
 int l2=length(b);
     if(l2==3)
     {
       return b;
     }
   if(l2!=3)
     {
       return middle(b,l2);
     }
 return 0;
 }
  

main() {

 int x=-100,y;
 if(x<0)
x=-x;
 int l=length(x);
 if(l.isEven||x<100)
 {print('error');}
   if(l==3)
 {print('$x');}

 if(l.isOdd&& x>100)
 {
  y=middle(x,l);
 print('$y');
 }

} </lang>

DCL

<lang>$ list = "123,12345,1234567,987654321,10001,-10001,-123,-100,100,-12345,1,2,-1,-10,2002,-2002,0" $ i = 0 $ loop: $ number = f$element( i, ",", list ) $ if number .eqs. "," then $ exit $ abs_number = number - "-" $ len = f$length( abs_number ) $ if len .lt. 3 .or. .not. len $ then $ write sys$output f$fao( "!9SL: ", f$integer( number )), "has no middle three" $ else $ write sys$output f$fao( "!9SL: ", f$integer( number )), f$extract( ( len - 3 ) / 2, 3, abs_number ) $ endif $ i = i + 1 $ goto loop</lang>

Output:
$ @middle_three_digits
      123: 123
    12345: 234
  1234567: 345
987654321: 654
    10001: 000
   -10001: 000
     -123: 123
     -100: 100
      100: 100
   -12345: 234
        1: has no middle three
        2: has no middle three
       -1: has no middle three
      -10: has no middle three
     2002: has no middle three
    -2002: has no middle three
        0: has no middle three

Eiffel

<lang Eiffel> class APPLICATION

create make

feature

make -- Test of middle_three_digits. local test_1, test_2: ARRAY [INTEGER] do test_1 := <<123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345>> test_2 := <<1, 2, -1, -10, 2002, -2002, 0>> across test_1 as t loop io.put_string ("The middle three digits of " + t.item.out + " are: %T ") io.put_string (middle_three_digits (t.item) + "%N") end across test_2 as t loop io.put_string ("The middle three digits of " + t.item.out + " are: %T") io.put_string (middle_three_digits (t.item) + "%N") end end

middle_three_digits (n: INTEGER): STRING -- The middle three digits of 'n'. local k, i: INTEGER in: STRING do create in.make_empty in := n.out if n < 0 then in.prune ('-') end create Result.make_empty if in.count < 3 then io.put_string (" Not enough digits. ") elseif in.count \\ 2 = 0 then io.put_string (" Even number of digits. ") else i := (in.count - 3) // 2 from k := i + 1 until k > i + 3 loop Result.extend (in.at (k)) k := k + 1 end end ensure length_is_three: Result.count = 3 or Result.count = 0 end

end </lang>

Output:
The middle three digits of 123 are:    123
The middle three digits of 12345 are:  234
The middle three digits of 1234567 are:    345
The middle three digits of 987654321 are:  654
The middle three digits of 10001 are:  000
The middle three digits of -10001 are: 000
The middle three digits of -123 are:   123
The middle three digits of -100 are:   100
The middle three digits of 100 are:    100
The middle three digits of -12345 are: 234
The middle three digits of 1 are:      Not enough digits.
The middle three digits of 2 are:      Not enough digits.
The middle three digits of -1 are:     Not enough digits.
The middle three digits of -10 are:    Not enough digits.
The middle three digits of 2002 are:   Even number of digits.
The middle three digits of -2002 are:  Even number of digits.
The middle three digits of 0 are:      Not enough digits.

Elena

ELENA 5.0 : <lang elena>import system'routines; import extensions;

middleThreeDigits(int n) {

   string s := n.Absolute.toString();
   int len := s.Length;
   if(len<3)
   {
       InvalidArgumentException.new:"n must have 3 digits or more".raise()
   }
   else if(len.isEven())
   {
       InvalidArgumentException.new:"n must have an odd number of digits".raise()
   };

   int mid := len / 2;

   ^ s.Substring(mid-1,3)

}

public program() {

   new int[]{123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0}
       .forEach:(n)
       {
           console.printLine("middleThreeDigits(",n,"):",middleThreeDigits(n) | on:(e => e.Message))
       }

}</lang>

Output:
middleThreeDigits(123):123
middleThreeDigits(12345):234
middleThreeDigits(1234567):345
middleThreeDigits(987654321):654
middleThreeDigits(10001):000
middleThreeDigits(-10001):000
middleThreeDigits(-123):123
middleThreeDigits(-100):100
middleThreeDigits(100):100
middleThreeDigits(-12345):234
middleThreeDigits(1):n must have 3 digits or more
middleThreeDigits(2):n must have 3 digits or more
middleThreeDigits(-1):n must have 3 digits or more
middleThreeDigits(-10):n must have 3 digits or more
middleThreeDigits(2002):n must have an odd number of digits
middleThreeDigits(-2002):n must have an odd number of digits
middleThreeDigits(0):n must have 3 digits or more

Elixir

<lang Elixir>defmodule Middle do

 def three(num) do
   n = num |> abs |> to_string
   
   case {n,String.length(n) > 2,even?(n)} do
     {n, true, false} ->
       cut(n)
     {_, false, _} ->
       raise "Number must have at least three digits"
     {_, _, true} ->
       raise "Number must have an odd number of digits"
   end
 end
 
 defp even?(n), do: rem(String.length(n),2) == 0
 defp cut(n), do: String.slice(n,(div(String.length(n),2) - 1),3)

end

valids = [123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345] Enum.each(valids, fn n -> :io.format "~10w : ~s~n", [n, Middle.three(n)] end)

errors = [1, 2, -1, -10, 2002, -2002, 0] Enum.each(errors, fn n ->

 :io.format "~10w : ", [n]
 try do
   IO.puts Middle.three(n)
 rescue
   e -> IO.puts e.message
 end

end)</lang>

Output:
       123 : 123
     12345 : 234
   1234567 : 345
 987654321 : 654
     10001 : 000
    -10001 : 000
      -123 : 123
      -100 : 100
       100 : 100
    -12345 : 234
         1 : Number must have at least three digits
         2 : Number must have at least three digits
        -1 : Number must have at least three digits
       -10 : Number must have at least three digits
      2002 : Number must have an odd number of digits
     -2002 : Number must have an odd number of digits
         0 : Number must have at least three digits

Erlang

<lang erlang>% -module(middle_three_digits). -export([main/0]).

main() -> digits(123), digits(12345), digits(1234567), digits(987654321), digits(10001), digits(-10001), digits(-123), digits(-100), digits(100), digits(-12345), digits(1), digits(2), digits(-1), digits(-10), digits(2002), digits(-2002), digits(0).

digits(N) when N < 0 -> digits(-N); digits(N) when (N div 100) =:= 0 -> io:format("too small\n"); digits(N) -> K=length(integer_to_list(N)), if (K rem 2) =:= 0 -> io:format("even number of digits\n"); true -> loop((K-3) div 2 , N) end.

loop(0, N) -> io:format("~3..0B~n",[N rem 1000]); loop(X,N) when X>0 -> loop(X-1, N div 10). </lang>

Output:
123
234
345
654
000
000
123
100
100
234
too small
too small
too small
too small
even number of digits
even number of digits
too small
ok

ERRE

<lang ERRE> PROGRAM MIDDLE

!$DOUBLE

FUNCTION LUNG(N)

  LUNG=LEN(STR$(INT(ABS(N))))+1

END FUNCTION

FUNCTION NCNT(N)

   NCNT=VAL(MID$(STR$(INT(ABS(N))),(LUNG(N)-1)/2,3))

END FUNCTION

FUNCTION EVEN(N)

   EVEN=INT(N/2)=N/2

END FUNCTION

PROCEDURE NUMBER_EXAM(N->R$)

   R$=""   LG%=LUNG(N)-2
   IF EVEN(LG%) THEN R$="?EVEN,"  END IF
   IF LG%<3 THEN
            R$=R$+"ONLY"+STR$(LG%)+" DIGIT"
            IF LG%=1 THEN
                R$=R$+"S"
            END IF
   END IF
   IF RIGHT$(R$,1)="," THEN R$=LEFT$(R$,LEN(R$)-1)   EXIT PROCEDURE END IF
   IF LEFT$(R$,1)="?" THEN EXIT PROCEDURE END IF
   IF R$<>"" THEN R$="?"+R$   EXIT PROCEDURE END IF
   R$=STR$(NCNT(N))
   IF LEFT$(R$,1)=" " THEN R$=MID$(R$,2) END IF
   IF LEN(R$)=1 THEN R$="00"+R$  END IF
   IF LEN(R$)=2 THEN R$="0"+R$   END IF

END PROCEDURE

BEGIN

   DATA(123,12345,1234567,987654321,10001,-10001,-123,-100,100,-12345)
   DATA(1,2,-1,-10,2002,-2002,0)
   FOR I%=1 TO 17 DO
       READ(N)
       PRINT(N;"  ",)
       NUMBER_EXAM(N->R$)
       PRINT(R$)
   END FOR

END PROGRAM </lang>

Output:
 123          123
 12345        234
 1234567      345
 987654321    654
 10001        000
-10001        000
-123          123
-100          100
 100          100
-12345        234
 1            ?ONLY 1 DIGITS
 2            ?ONLY 1 DIGITS
-1            ?ONLY 1 DIGITS
-10           ?EVEN,ONLY 2 DIGIT
 2002         ?EVEN
-2002         ?EVEN
 0            ?ONLY 1 DIGITS

Factor

<lang>USING: combinators formatting io kernel math math.parser sequences ; IN: rosetta-code.middle-three-digits

CONSTANT: test-values {

   123 12345 1234567 987654321 10001 -10001
   -123 -100 100 -12345 1 2 -1 -10 2002 -2002 0

}

(middle-three) ( str -- str' )
   [ midpoint@ [ 1 - ] [ 2 + ] bi ] [ subseq ] bi ;
   
too-short ( -- )
   "Number must have at least three digits." print ;
   
number-even ( -- )
   "Number must have an odd number of digits." print ;
middle-three ( n -- )
   abs number>string {
       { [ dup length 3 < ] [ drop too-short ] }
       { [ dup length even? ] [ drop number-even ] }
       [ (middle-three) print ]
   } cond ;
   
main ( -- )
   test-values [ dup "%9d : " printf middle-three ] each ;

MAIN: main</lang>

Output:
      123 : 123
    12345 : 234
  1234567 : 345
987654321 : 654
    10001 : 000
   -10001 : 000
     -123 : 123
     -100 : 100
      100 : 100
   -12345 : 234
        1 : Number must have at least three digits.
        2 : Number must have at least three digits.
       -1 : Number must have at least three digits.
      -10 : Number must have at least three digits.
     2002 : Number must have an odd number of digits.
    -2002 : Number must have an odd number of digits.
        0 : Number must have at least three digits.

Forth

This is a problem, which is easily solved in Forth. It converts the number to a string and checks it length. If the number does not represent a printable string, it returns an empty string. <lang forth>: middle3 ( n1 -- a n2)

 abs s>d <# #s #> dup 2/ 0<> over 1 and 0<> and
 if 2/ 1- chars + 3 else drop 0 then
</lang>

Fortran

Please find compilation instructions along with the output for the examples in the comments at the beginning of the file. This program was produced in an Ubuntu distribution of the GNU/linux system. <lang FORTRAN> !-*- mode: compilation; default-directory: "/tmp/" -*- !Compilation started at Sat Jun 1 14:48:41 ! !a=./f && make $a && OMP_NUM_THREADS=2 $a < unixdict.txt # some of the compilation options and redirection from unixdict.txt are vestigial. !gfortran -std=f2008 -Wall -fopenmp -ffree-form -fall-intrinsics -fimplicit-none f.f08 -o f ! 123 123 ! 12345 234 ! 1234567 345 ! 987654321 654 ! 10001 000 ! -10001 000 ! -123 123 ! -100 100 ! 100 100 ! -12345 234 ! 1 Too short ! 2 Too short ! -1 Too short ! -10 Too short ! 2002 Digit count too even ! -2002 Digit count too even ! 0 Too short ! !Compilation finished at Sat Jun 1 14:48:41


program MiddleMuddle

 integer, dimension(17) :: itest, idigits
 integer :: i, n
 data itest/123,12345,1234567,987654321,10001,-10001,-123,-100,100,-12345,1,2,-1,-10,2002,-2002,0/
 do i = 1, size(itest)
   call antibase(10, abs(itest(i)), idigits, n)
   write(6,'(i20,2x,a20)') itest(i), classifym3(idigits, n)
   if (0 .eq. itest(i)) exit
 end do

contains

 logical function even(n)
   integer, intent(in) :: n
   even = 0 .eq. iand(n,1)
 end function even
 function classifym3(iarray, n) result(s)
   integer, dimension(:), intent(in) :: iarray
   integer, intent(in) :: n
   character(len=20) :: s
   integer :: i,m
   if (n < 3) then
     s = 'Too short'
   else if (even(n)) then
     s = 'Digit count too even'
   else
     m = (n+1)/2
     write(s,'(3i1)')(iarray(i), i=m+1,m-1,-1)
   end if
 end function classifym3
 subroutine antibase(base, m, digits, n) ! digits ordered by increasing significance
   integer, intent(in) :: base, m
   integer, intent(out) :: n  ! the number of digits
   integer, dimension(:), intent(out) :: digits
   integer :: em
   em = m
   do n=1, size(digits)
     digits(n) = mod(em, base)
     em = em / base
     if (0 .eq. em) return
   end do
   stop 'antibase ran out of space to store result'
 end subroutine antibase

end program MiddleMuddle </lang>

FreeBASIC

<lang freebasic>' FB 1.05.0 Win64

Function middleThreeDigits (n As Integer) As String

 If n < 0 Then n = -n
 If n < 100 Then Return ""   error code
 If n < 1000 Then Return Str(n)
 If n < 10000 Then Return "" 
 Dim ns As String = Str(n)
 If Len(ns) Mod 2 = 0 Then Return ""   need to have an odd number of digits for there to be 3 middle
 Return Mid(ns, Len(ns) \ 2, 3) 

End Function

Dim a(1 To 16) As Integer => _ {123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -123451, 2, -1, -10, 2002, -2002, 0}

Dim As Integer i Dim As String result

Print "The 3 middle digits of the following numbers are : " Print For i = 1 To 16

 result = middleThreeDigits(a(i))
 Print a(i), " => "; 
 If result <> "" Then
   Print result
 Else
   Print "Error: does not have 3 middle digits"
 End If

Next Print Print "Press any key to quit" Sleep</lang>

Output:
The 3 middle digits of the following numbers are :

 123           => 123
 12345         => 234
 1234567       => 345
 987654321     => 654
 10001         => 000
-10001         => 000
-123           => 123
-100           => 100
 100           => 100
-123451        => Error: does not have 3 middle digits
 2             => Error: does not have 3 middle digits
-1             => Error: does not have 3 middle digits
-10            => Error: does not have 3 middle digits
 2002          => Error: does not have 3 middle digits
-2002          => Error: does not have 3 middle digits
 0             => Error: does not have 3 middle digits

Gambas

Click this link to run this code <lang gambas>Public Sub Main() Dim iList As Integer[] = [123, 12345, 1234567, 987654321, 10001,

-10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0]    'Array of integers to process

Dim sTemp As String 'Temp string Dim siCount As Short 'Counter Dim sAnswer As New String[] 'Array, resons for failure or 'middle three digits'

For siCount = 0 To iList.Max 'Loop through the integers

 sTemp = Str(Abs(iList[siCount]))                                  'Convert integer to positive and place in sTemp as a string
 If Len(sTemp) < 3 Then                                            'If sTemp has less than 3 characters then..
   sAnswer.Add("This integer has less than 3 characters")          'Place text in sAnswers
 Else If Even(Len(sTemp)) Then                                     'Else If sTemp is of even length then
   sAnswer.Add("This integer has an even length")                  'Place text in sAnswers
 Else                                                              'Else..
   sAnswer.Add(Mid(sTemp, Int(Len(sTemp) / 2), 3))                 'Place the middle 3 digits in sAnswer
 Endif

Next

For siCount = 0 To iList.Max 'Loop through the integers

 Print Space$(10 - Len(Str(iList[siCount]))) & 
   iList[siCount] & " : " & sAnswer[siCount]                       'Print out results

Next

End</lang> Output:

     12345 : 234
   1234567 : 345
 987654321 : 654
     10001 : 000
    -10001 : 000
      -123 : 123
      -100 : 100
       100 : 100
    -12345 : 234
         1 : This integer has less than 3 characters
         2 : This integer has less than 3 characters
        -1 : This integer has less than 3 characters
       -10 : This integer has less than 3 characters
      2002 : This integer has an even length
     -2002 : This integer has an even length
         0 : This integer has less than 3 characters

Go

Unlike most Go examples on RC, this is written as a package to show operation of the go test tool.

File m3.go: <lang go>package m3

import (

   "errors"
   "strconv"

)

var (

   ErrorLT3  = errors.New("N of at least three digits required.")
   ErrorEven = errors.New("N with odd number of digits required.")

)

func Digits(i int) (string, error) {

   if i < 0 {
       i = -i
   }
   if i < 100 {
       return "", ErrorLT3
   }
   s := strconv.Itoa(i)
   if len(s)%2 == 0 {
       return "", ErrorEven
   }
   m := len(s) / 2
   return s[m-1 : m+2], nil

}</lang> File m3_test.go: <lang go>package m3_test

import (

   "testing"
   "m3"

)

func TestPassing(t *testing.T) {

   type s struct {
       i int
       m string
   }
   tcs := []s{
       {123, "123"},
       {12345, "234"},
       {1234567, "345"},
       {987654321, "654"},
       {10001, "000"},
       {-10001, "000"},
   }
   for _, tc := range tcs {
       m, err := m3.Digits(tc.i)
       if err != nil {
           t.Fatalf("d(%d) returned %q.", tc.i, err)
       }
       if m != tc.m {
           t.Fatalf("d(%d) expected %q, got %q.", tc.i, tc.m, m)
       }
       t.Logf("d(%d) = %q.", tc.i, m)
   }

}

func TestFailing(t *testing.T) {

   type s struct {
       i   int
       err error
   }
   tcs := []s{
       {1, m3.ErrorLT3},
       {2, m3.ErrorLT3},
       {-1, m3.ErrorLT3},
       {-10, m3.ErrorLT3},
       {2002, m3.ErrorEven},
       {-2002, m3.ErrorEven},
       {0, m3.ErrorLT3},
   }
   for _, tc := range tcs {
       m, err := m3.Digits(tc.i)
       if err == nil {
           t.Fatal("d(%d) expected error %q, got non-error %q.",
               tc.i, tc.err, m)
       }
       if err != tc.err {
           t.Fatal("d(d) expected error %q, got %q", tc.i, tc.err, err)
       }
       t.Logf("d(%d) returns %q", tc.i, err)
   }

}</lang>

Output:

Output of go test is normally terse:

> go test
PASS
ok      m3      0.008s

With -v (for verbose):

> go test -v
=== RUN TestPassing-4
--- PASS: TestPassing-4 (0.00 seconds)
        m3_test.go:30: d(123) = "123".
        m3_test.go:30: d(12345) = "234".
        m3_test.go:30: d(1234567) = "345".
        m3_test.go:30: d(987654321) = "654".
        m3_test.go:30: d(10001) = "000".
        m3_test.go:30: d(-10001) = "000".
=== RUN TestFailing-4
--- PASS: TestFailing-4 (0.00 seconds)
        m3_test.go:57: d(1) returns "N of at least three digits required."
        m3_test.go:57: d(2) returns "N of at least three digits required."
        m3_test.go:57: d(-1) returns "N of at least three digits required."
        m3_test.go:57: d(-10) returns "N of at least three digits required."
        m3_test.go:57: d(2002) returns "N with odd number of digits required."
        m3_test.go:57: d(-2002) returns "N with odd number of digits required."
        m3_test.go:57: d(0) returns "N of at least three digits required."
PASS
ok      m3      0.008s

Gosu

<lang gosu>var valid = {123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345} valid.each(\ num ->print(middleThree(num)))

var errant = {1, 2, -1, -10, 2002, -2002, 0} errant.each(\ num ->print(middleThree(num)))

function middleThree(x: int) : String {

 var s = Math.abs(x) as String
 if(s.length < 3) return "Error: ${x} has less than 3 digits"
 if(s.length % 2 == 0) return "Error: ${x} has an even number of digits"
 var start = (s.length / 2) - 1
 return s.substring(start, start + 3)

}</lang>

Output:
123
234
345
654
000
000
123
100
100
234
Error: 1 has less than 3 digits
Error: 2 has less than 3 digits
Error: -1 has less than 3 digits
Error: -10 has less than 3 digits
Error: 2002 has an even number of digits
Error: -2002 has an even number of digits
Error: 0 has less than 3 digits

Groovy

<lang groovy>def middleThree(Number number) {

   def text = Math.abs(number) as String
   assert text.size() >= 3 : "'$number' must be more than 3 numeric digits"
   assert text.size() % 2 == 1 : "'$number' must have an odd number of digits"
   int start = text.size() / 2 - 1
   text[start..(start+2)]

}</lang> Test Code: <lang groovy>[123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0].each { number ->

   def text = (number as String).padLeft(10)
   try {
       println "$text: ${middleThree(number)}"
   } catch(AssertionError error) {
       println "$text cannot be converted: $error.message"
   }

}</lang> Output:

       123: 123
     12345: 234
   1234567: 345
 987654321: 654
     10001: 000
    -10001: 000
      -123: 123
      -100: 100
       100: 100
    -12345: 234
         1 cannot be converted: '1' must be more than 3 numeric digits. Expression: (text.size() >= 3)
         2 cannot be converted: '2' must be more than 3 numeric digits. Expression: (text.size() >= 3)
        -1 cannot be converted: '-1' must be more than 3 numeric digits. Expression: (text.size() >= 3)
       -10 cannot be converted: '-10' must be more than 3 numeric digits. Expression: (text.size() >= 3)
      2002 cannot be converted: '2002' must have an odd number of digits. Expression: ((text.size() % 2) == 1)
     -2002 cannot be converted: '-2002' must have an odd number of digits. Expression: ((text.size() % 2) == 1)
         0 cannot be converted: '0' must be more than 3 numeric digits. Expression: (text.size() >= 3)

Haskell

<lang haskell>mid3 :: Int -> Either String String mid3 n

 | m < 100 = Left "is too small"
 | even lng = Left "has an even number of digits"
 | otherwise = Right . take 3 $ drop ((lng - 3) `div` 2) s
 where
   m = abs n
   s = show m
   lng = length s

-- TEST -------------------------------------------------------- main :: IO () main = do

 let xs =
       [ 123
       , 12345
       , 1234567
       , 987654321
       , 10001
       , -10001
       , -123
       , -100
       , 100
       , -12345
       , 1
       , 2
       , -1
       , -10
       , 2002
       , -2002
       , 0
       ]
     w = maximum $ (length . show) <$> xs
 (putStrLn . unlines) $
   (\n ->
       justifyRight w ' ' (show n) ++
       " -> " ++ either ((>>= id) . ("(" :) . (: [")"])) id (mid3 n)) <$>
   xs
 where
   justifyRight :: Int -> Char -> String -> String
   justifyRight n c s = drop (length s) (replicate n c ++ s)</lang>

Output:

      123 -> 123
    12345 -> 234
  1234567 -> 345
987654321 -> 654
    10001 -> 000
   -10001 -> 000
     -123 -> 123
     -100 -> 100
      100 -> 100
   -12345 -> 234
        1 -> (is too small)
        2 -> (is too small)
       -1 -> (is too small)
      -10 -> (is too small)
     2002 -> (has an even number of digits)
    -2002 -> (has an even number of digits)
        0 -> (is too small)

Icon and Unicon

The following solution works in both languages.

<lang unicon>procedure main(a)

  every n := !a do write(right(n,15)," -> ",midM(n))

end

procedure midM(n,m)

  /m := 3
  n := abs(n)
  return n ? if (*n >= m) then
                if (((*n-m) % 2) = 0) then (move((*n - m)/2),move(m))
                else "wrong number of digits"
             else "too short"

end</lang>

with output:

->m3d 123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345 1 2 -1 -10 2002 -2002 0
            123 -> 123
          12345 -> 234
        1234567 -> 345
      987654321 -> 654
          10001 -> 000
         -10001 -> 000
           -123 -> 123
           -100 -> 100
            100 -> 100
         -12345 -> 234
              1 -> too short
              2 -> too short
             -1 -> too short
            -10 -> too short
           2002 -> wrong number of digits
          -2002 -> wrong number of digits
              0 -> too short
->

J

Solution: <lang j>asString=: ":"0 NB. convert vals to strings getPfxSize=: [: -:@| 3 -~ # NB. get size of prefix to drop before the 3 middle digits getMid3=: (3 {. getPfxSize }. ,&'err') :: ('err'"_) NB. get 3 middle digits or return 'err' getMiddle3=: getMid3@asString@:|</lang> Example: <lang j> vals=: 123 12345 1234567 987654321 10001 _10001 _123 _100 100 _12345 1 2 _1 _10 2002 _2002 0

  getMiddle3 vals

123 234 345 654 000 000 123 100 100 234 err err err err err err err</lang>

Java

<lang Java>public class MiddleThreeDigits {

   public static void main(String[] args) {
       final long[] passing = {123, 12345, 1234567, 987654321, 10001, -10001,
           -123, -100, 100, -12345, Long.MIN_VALUE, Long.MAX_VALUE};
       final int[] failing = {1, 2, -1, -10, 2002, -2002, 0, Integer.MIN_VALUE,
           Integer.MAX_VALUE};
       for (long n : passing)
           System.out.printf("middleThreeDigits(%s): %s\n", n, middleThreeDigits(n));
       for (int n : failing)
           System.out.printf("middleThreeDigits(%s): %s\n", n, middleThreeDigits(n));
   }
   public static <T> String middleThreeDigits(T n) {
       String s = String.valueOf(n);
       if (s.charAt(0) == '-')
           s = s.substring(1);
       int len = s.length();
       if (len < 3 || len % 2 == 0)
           return "Need odd and >= 3 digits";
       int mid = len / 2;
       return s.substring(mid - 1, mid + 2);
   }

}</lang>

middleThreeDigits(123): 123
middleThreeDigits(12345): 234
middleThreeDigits(1234567): 345
middleThreeDigits(987654321): 654
middleThreeDigits(10001): 000
middleThreeDigits(-10001): 000
middleThreeDigits(-123): 123
middleThreeDigits(-100): 100
middleThreeDigits(100): 100
middleThreeDigits(-12345): 234
middleThreeDigits(-9223372036854775808): 368
middleThreeDigits(9223372036854775807): 368
middleThreeDigits(1): Need odd and >= 3 digits
middleThreeDigits(2): Need odd and >= 3 digits
middleThreeDigits(-1): Need odd and >= 3 digits
middleThreeDigits(-10): Need odd and >= 3 digits
middleThreeDigits(2002): Need odd and >= 3 digits
middleThreeDigits(-2002): Need odd and >= 3 digits
middleThreeDigits(0): Need odd and >= 3 digits
middleThreeDigits(-2147483648): Need odd and >= 3 digits
middleThreeDigits(2147483647): Need odd and >= 3 digits

JavaScript

<lang JavaScript>function middleThree(x){

 var n=+Math.abs(x); var l=n.length-1;
 if(l<2||l%2) throw new Error(x+': Invalid length '+(l+1));
 return n.slice(l/2-1,l/2+2);

}

[123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0].forEach(function(n){

 try{console.log(n,middleThree(n))}catch(e){console.error(e.message)}

});</lang>

123 "123"
12345 "234"
1234567 "345"
987654321 "654"
10001 "000"
-10001 "000"
-123 "123"
-100 "100"
100 "100"
-12345 "234"
1: Invalid length 1
2: Invalid length 1
-1: Invalid length 1
-10: Invalid length 2
2002: Invalid length 4
-2002: Invalid length 4
0: Invalid length 1


Or, using an option type, composing a solution from existing generic primitives, and formatting the output a little:

Translation of: Python

<lang javascript>(() => {

   'use strict';
   // mid3digits :: Int -> Either String String
   const mid3digits = n => {
       const
           m = abs(n),
           s = m.toString();
       return 100 > m ? (
           Left('Less than 3 digits')
       ) : even(length(s)) ? (
           Left('Even digit count')
       ) : Right(take(3, drop(quot(length(s) - 3, 2), s)));
   };
   // TEST -----------------------------------------------
   const main = () => {
       const
           xs = [
               123, 12345, 1234567, 987654321, 10001, -10001, -123,
               -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0
           ],
           w = maximum(map(x => x.toString().length, xs));
       return (
           unlines(map(
               n => justifyRight(w, ' ', n.toString()) + ' -> ' +
               either(
                   s => '(' + s + ')',
                   id,
                   mid3digits(n)
               ),
               xs
           ))
       );
   };
   // GENERIC FUNCTIONS ----------------------------------
   // Left :: a -> Either a b
   const Left = x => ({
       type: 'Either',
       Left: x
   });
   // Right :: b -> Either a b
   const Right = x => ({
       type: 'Either',
       Right: x
   });
   // abs :: Num -> Num
   const abs = Math.abs;
   // drop :: Int -> [a] -> [a]
   // drop :: Int -> Generator [a] -> Generator [a]
   // drop :: Int -> String -> String
   const drop = (n, xs) =>
       Infinity > length(xs) ? (
           xs.slice(n)
       ) : (take(n, xs), xs);
   // either :: (a -> c) -> (b -> c) -> Either a b -> c
   const either = (fl, fr, e) =>
       'Either' === e.type ? (
           undefined !== e.Left ? (
               fl(e.Left)
           ) : fr(e.Right)
       ) : undefined;
   // even :: Int -> Bool
   const even = n => 0 === n % 2;
   // foldl1 :: (a -> a -> a) -> [a] -> a
   const foldl1 = (f, xs) =>
       1 < xs.length ? xs.slice(1)
       .reduce(f, xs[0]) : xs[0];
   // id :: a -> a
   const id = x => x;
   // justifyRight :: Int -> Char -> String -> String
   const justifyRight = (n, cFiller, s) =>
       n > s.length ? (
           s.padStart(n, cFiller)
       ) : s;
   // Returns Infinity over objects without finite length.
   // This enables zip and zipWith to choose the shorter
   // argument when one is non-finite, like cycle, repeat etc
   // length :: [a] -> Int
   const length = xs =>
       (Array.isArray(xs) || 'string' === typeof xs) ? (
           xs.length
       ) : Infinity;
   // maximum :: Ord a => [a] -> a
   const maximum = xs =>
       0 < xs.length ? (
           foldl1((a, x) => x > a ? x : a, xs)
       ) : undefined;
   // map :: (a -> b) -> [a] -> [b]
   const map = (f, xs) => xs.map(f);
   // quot :: Int -> Int -> Int
   const quot = (n, m) => Math.floor(n / m);
   // take :: Int -> [a] -> [a]
   // take :: Int -> String -> String
   const take = (n, xs) =>
       'GeneratorFunction' !== xs.constructor.constructor.name ? (
           xs.slice(0, n)
       ) : [].concat.apply([], Array.from({
           length: n
       }, () => {
           const x = xs.next();
           return x.done ? [] : [x.value];
       }));
   // unlines :: [String] -> String
   const unlines = xs => xs.join('\n');
   // MAIN ---
   return main();

})();</lang>

Output:
      123 -> 123
    12345 -> 234
  1234567 -> 345
987654321 -> 654
    10001 -> 000
   -10001 -> 000
     -123 -> 123
     -100 -> 100
      100 -> 100
   -12345 -> 234
        1 -> (Less than 3 digits)
        2 -> (Less than 3 digits)
       -1 -> (Less than 3 digits)
      -10 -> (Less than 3 digits)
     2002 -> (Even digit count)
    -2002 -> (Even digit count)
        0 -> (Less than 3 digits)

jq

<lang jq>def middle3:

 if . <  0 then -. else . end
 | tostring as $s
 | ($s | length) as $n
 | if $n<3 or ($n % 2) == 0 then "invalid length: \($n)"
   else (($n - 1) / 2) as $n |  $s[$n - 1 : $n + 2]
   end ;

(123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0)

 | "\(.) => \( .|middle3 )"</lang>

Typescript:<lang sh> $ jq -r -n -f Middle_three_digits.jq 123 => 123 12345 => 234 1234567 => 345 987654321 => 654 10001 => 000 -10001 => 000 -123 => 123 -100 => 100 100 => 100 -12345 => 234 1 => invalid length: 1 2 => invalid length: 1 -1 => invalid length: 1 -10 => invalid length: 2 2002 => invalid length: 4 -2002 => invalid length: 4 0 => invalid length: 1 </lang>

Julia

Works with: Julia version 1.0.3

<lang julia>using Printf

function middle3(n::Integer)

   l = ndigits(n)
   iseven(l) && error("n must have an odd number of digits")
   l < 3 && error("n must have 3 digits or more")
   mid = (l + 1) ÷ 2
   abs(n) ÷ 10^(mid-2) % 10^3

end

for n = [123, 12345, 1234567, 987654321, 10001, -10001, -123,

        -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0]
   @printf("%10d -> %s\n", n, try middle3(n) catch e e.msg end)

end</lang>

Output:
       123 -> 123
     12345 -> 234
   1234567 -> 345
 987654321 -> 654
     10001 -> 000
    -10001 -> 000
      -123 -> 123
      -100 -> 100
       100 -> 100
    -12345 -> 234
         1 -> n must have 3 digits or more
         2 -> n must have 3 digits or more
        -1 -> n must have 3 digits or more
       -10 -> n must have an odd number of digits
      2002 -> n must have an odd number of digits
     -2002 -> n must have an odd number of digits
         0 -> n must have 3 digits or more

K

<lang K> / Rosetta code - Middle three digits / mid3.k mid3: {qs:$x;:[qs[0]="-";qs: 1 _ qs];:[(#qs)<3;:"small";(1+#qs)!2;:"even"];p:(-3+#qs)%2;:(|p _|p _ qs)} </lang> The output of the session:

Output:
K Console - Enter \ for help

  \l mid3

  mid3' 123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345 1 2 -1 -10
 2002 -2002 0
("123"
 "234"
 "345"
 "654"
 "000"
 "000"
 "123"
 "100"
 "100"
 "234"
 "small"
 "small"
 "small"
 "small"
 "even"
 "even"
 "small")

Klong

<lang k>items::[123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345 1 2 -1 -10 2002 -2002 0]

mid3::{[d k];:[3>k::#$#x;"small":|0=k!2;"even";(-d)_(d::_(k%2)-1)_$#x]} .p(mid3'items)</lang> Output:

[123 234 345 654 000 000 123 100 100 234 small small small small even even small]

Kotlin

<lang scala>fun middleThree(x: Int): Int? {

   val s = Math.abs(x).toString()
   return when {
       s.length < 3 -> null // throw Exception("too short!")
       s.length % 2 == 0 -> null // throw Exception("even number of digits")
       else -> ((s.length / 2) - 1).let { s.substring(it, it + 3) }.toInt()
   }

}

fun main(args: Array<String>) {

   println(middleThree(12345)) // 234
   println(middleThree(1234)) // null
   println(middleThree(1234567)) // 345
   println(middleThree(123))// 123
   println(middleThree(123555)) //null

}</lang>

Lambdatalk

<lang scheme> {def S 123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345

      1 2 -1 -10 2002 -2002 0} 

-> S

{def middle3digits

{lambda {:w}
 {let { {:w {abs :w}}
        {:l {W.length {abs :w}}}
      } {if {= {% :l 2} 0}
         then has an even number of digits
         else {if {< :l 3}
         then has not enough digits
         else {W.get {- {/ :l 2} 1} :w}
              {W.get {/ :l 2} :w}
              {W.get {+ {/ :l 2} 1} :w} }}}}}

-> middle3digits


{table {S.map {lambda {:i}

      {tr {td {@ style="text-align:right;"}:i:}
          {td {middle3digits :i}}}}
      {S}} }

->

  123: 	123
  12345: 	234
  1234567: 	345
987654321: 	654
    10001: 	000
   -10001: 	000
     -123: 	123
     -100: 	100
      100: 	100
   -12345: 	234
        1: 	has not enough digits
        2: 	has not enough digits
       -1: 	has not enough digits
      -10: 	has an even number of digits
     2002: 	has an even number of digits
    -2002: 	has an even number of digits
        0: 	has not enough digits

</lang>

Lasso

<lang Lasso>define middlethree(value::integer) => { local( pos_value = math_abs(#value), stringvalue = #pos_value -> asstring, intlength = #stringvalue -> size, middle = integer((#intlength + 1) / 2), prefix = string(#value) -> padleading(15)& + ': ' )

#intlength < 3 ? return #prefix + 'Error: too few digits' not(#intlength % 2) ? return #prefix + 'Error: even number of digits'

return #prefix + #stringvalue -> sub(#middle -1, 3)

}

'
'
with number in array(123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0) do {^

	middlethree(#number)
	'<br />'
^}
'
'</lang>

Output

            123: 123
          12345: 234
        1234567: 345
      987654321: 654
          10001: 000
         -10001: 000
           -123: 123
           -100: 100
            100: 100
         -12345: 234
              1: Error: too few digits
              2: Error: too few digits
             -1: Error: too few digits
            -10: Error: too few digits
           2002: Error: even number of digits
          -2002: Error: even number of digits
              0: Error: too few digits

<lang logo>to middle3digits :n

 if [less? :n 0] [make "n minus :n]
 local "len make "len count :n
 if [less? :len 3] [(throw "error [Number must have at least 3 digits])]
 if [equal? 0 modulo :len 2] [(throw "error [Number must have odd number of digits])]
 while [greater? count :n 3] [
   make "n butlast butfirst :n
 ]
 output :n

end

foreach [123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345

        1 2 -1 -10 2002 -2002 0] [
   type sentence (word ? ": char 9) runresult [if [less? count ? 7] [char 9]]
   make "mid runresult [catch "error [middle3digits ?]]
   print ifelse [empty? :mid] [item 2 error] [:mid]

]

bye</lang>

Output:
123:	 	123
12345:	 	234
1234567:	345
987654321:	654
10001:	 	000
-10001:	 	000
-123:	 	123
-100:	 	100
100:	 	100
-12345:	 	234
1:	 	Number must have at least 3 digits
2:	 	Number must have at least 3 digits
-1:	 	Number must have at least 3 digits
-10:	 	Number must have at least 3 digits
2002:	 	Number must have odd number of digits
-2002:	 	Number must have odd number of digits
0:	 	Number must have at least 3 digits

Lua

<lang lua>function middle_three(n) if n < 0 then n = -n end

n = tostring(n) if #n % 2 == 0 then return "Error: the number of digits is even." elseif #n < 3 then return "Error: the number has less than 3 digits." end

local l = math.floor(#n/2) return n:sub(l, l+2) end

-- test do local t = {123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0}

for _,n in pairs(t) do print(n, middle_three(n)) end end</lang>

Output:
123	123
12345	234
1234567	345
987654321	654
10001	000
-10001	000
-123	123
-100	100
100	100
-12345	234
1	Error: the number has less than 3 digits.
2	Error: the number has less than 3 digits.
-1	Error: the number has less than 3 digits.
-10	Error: the number is even.
2002	Error: the number is even.
-2002	Error: the number is even.
0	Error: the number has less than 3 digits.

Maple

<lang maple>middleDigits := proc(n) local nList, start; nList := [seq(parse(i), i in convert (abs(n), string))]; if numelems(nList) < 3 then printf ("%9a: Error: Not enough digits.", n); elif numelems(nList) mod 2 = 0 then printf ("%9a: Error: Even number of digits.", n); else start := (numelems(nList)-1)/2; printf("%9a: %a%a%a", n, op(nList[start..start+2])); end if; end proc:

a := [123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0]: for i in a do middleDigits(i); printf("\n"); end do;</lang>

Output:
      123: 123
    12345: 234
  1234567: 345
987654321: 654
    10001: 000
   -10001: 000
     -123: 123
     -100: 100
      100: 100
   -12345: 234
        1: Error: Not enough digits.
        2: Error: Not enough digits.
       -1: Error: Not enough digits.
      -10: Error: Not enough digits.
     2002: Error: Even number of digits.
    -2002: Error: Even number of digits.
        0: Error: Not enough digits.

Mathematica

<lang Mathematica>middleThree[n_Integer] :=

Block[{digits = IntegerDigits[n], len},
 len = Length[digits];
 If[len < 3 || EvenQ[len], "number digits odd or less than 3", 
  len = Ceiling[len/2]; 
  StringJoin @@ (ToString /@ digitslen - 1 ;; len + 1)]]

testData = {123, 12345, 1234567, 987654321, 10001, -10001, -123, -100,

   100, -12345, 1, 2, -1, -10, 2002, -2002, 0};

Column[middleThree /@ testData]</lang>

Output:

123 234 345 654 000 000 123 100 100 234 err: n too small err: n too small err: n too small err: n too small err: even number of digits err: even number of digits err: n too small

MATLAB / Octave

<lang MATLAB>function s=middle_three_digits(a) % http://rosettacode.org/wiki/Middle_three_digits

s=num2str(abs(a));

if ~mod(length(s),2) s='*** error: number of digits must be odd ***'; return; end; if length(s)<3, s='*** error: number of digits must not be smaller than 3 ***'; return; end;

s = s((length(s)+1)/2+[-1:1]);</lang> Test with <lang MATLAB> x=[123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0]; for k=1:length(x); fprintf(1,'%9i:%s\n',x(k),middle_three_digits(x(k)));end;</lang> Result

      123:123
    12345:234
  1234567:457
987654321:654
    10001:000
   -10001:000
     -123:123
     -100:100
      100:100
   -12345:234
        1:*** error: number of digits must not be smaller than 3 ***
        2:*** error: number of digits must not be smaller than 3 ***
       -1:*** error: number of digits must not be smaller than 3 ***
      -10:*** error: number of digits must be odd ***
     2002:*** error: number of digits must be odd ***
    -2002:*** error: number of digits must be odd ***
        0:*** error: number of digits must not be smaller than 3 ***

MiniScript

<lang MiniScript>middle3 = function(num)

   if num < 0 then num = -num
   s = str(num)
   if s.len < 3 then return "Input too short"
   if s.len % 2 == 0 then return "Input length not odd"
   mid = (s.len + 1) / 2 - 1
   return s[mid-1:mid+2]

end function

for test in [123, 12345, 1234567, 987654321, 10001, -10001, -123, -100,

100, -12345, 1, 2, -1, -10, 2002, -2002, 0]
   print test + " --> " + middle3(test)

end for</lang>

Output:
123 --> 123
12345 --> 234
1234567 --> 345
987654321 --> 654
10001 --> 000
-10001 --> 000
-123 --> 123
-100 --> 100
100 --> 100
-12345 --> 234
1 --> Input too short
2 --> Input too short
-1 --> Input too short
-10 --> Input too short
2002 --> Input length not odd
-2002 --> Input length not odd
0 --> Input too short

МК-61/52

<lang>П0 lg [x] 3 - x>=0 23 ИП0 1 0 / [x] ^ lg [x] 10^x П1 / {x} ИП1

  • БП 00 1 + x=0 29 ИП0 С/П 0

/</lang>

Instruction: enter the number in the РX (on display), the result after the execution of the same. In the case of an even or less than 3 number of digits the indicator displays an error message.

ML

mLite

<lang ocaml> val test_array = ["123","12345","1234567","987654321","10001","~10001","~123","~100","100","~12345","1","2","~1","~10","2002","~2002","0"];

fun even (x rem 2 = 0) = true | _ = false;

fun middleThreeDigits (h :: t, s, 1 ) = s @ " --> too small" | (h :: t, s, 2 ) = s @ " --> has even digits" | (h :: t, s, 3 ) where (len (h :: t) = 3) = s @ " --> " @ (implode (h :: t)) | (h :: t, s, 3 ) = (middleThreeDigits ( sub (t, 0, (len t)-1), s, 3)) | (h :: t, s, m) = if len (h :: t) < 3 then middleThreeDigits (h :: t, s, 1) else if even ` len (h :: t) then middleThreeDigits (h :: t, s, 2) else middleThreeDigits (h :: t, s, 3)


| s = if sub (s, 0, 1) = "~" then middleThreeDigits (sub (explode s, 1, len s), s, 0) else middleThreeDigits (explode s, s, 0) ;

map (println o middleThreeDigits) test_array;</lang> Output:

123 --> 123
12345 --> 234
1234567 --> 345
987654321 --> 654
10001 --> 000
~10001 --> 000
~123 --> 123
~100 --> 100
100 --> 100
~12345 --> 234
1 --> too small
2 --> too small
~1 --> too small
~10 --> too small
2002 --> has even digits
~2002 --> has even digits
0 --> too small

MUMPS

This sample shows the MUMPS code required to pass the specification. <lang MUMPS>/* MUMPS */ MID3(N)  ;

       N LEN,N2                                                                
       S N2=$S(N<0:-N,1:N)                                                     
       I N2<100 Q "NUMBER TOO SMALL"                                           
       S LEN=$L(N2)                                                            
       I LEN#2=0 Q "EVEN NUMBER OF DIGITS"                                     
       Q $E(N2,LEN\2,LEN\2+2)

F I=123,12345,1234567,987654321,10001,-10001,-123,-100,100,-12345,1,2,-1,-10,2002,-2002,0 W !,$J(I,10),": ",$$MID3^MID3(I) </lang> Output:

       123: 123                                                                 
     12345: 234                                                                 
   1234567: 345                                                                 
 987654321: 654                                                                 
     10001: 000                                                                 
    -10001: 000                                                                 
      -123: 123                                                                 
      -100: 100                                                                 
       100: 100                                                                 
    -12345: 234                                                                 
         1: NUMBER TOO SMALL                                                    
         2: NUMBER TOO SMALL                                                    
        -1: NUMBER TOO SMALL                                                    
       -10: NUMBER TOO SMALL                                                    
      2002: EVEN NUMBER OF DIGITS                                               
     -2002: EVEN NUMBER OF DIGITS                                               
         0: NUMBER TOO SMALL      

NetRexx

This sample goes the extra mile and provides a method that can display the middle N digits from the input value. To satisfy the requirements of this task, a static invocation of this general method is also provided with the value 3 hard coded as the digit count. <lang NetRexx>/* NetRexx */ options replace format comments java crossref symbols nobinary

sl = '123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345' -

    '1 2 -1 -10 2002 -2002 0' -
    'abc 1e3 -17e-3 4004.5 12345678 9876543210' -- extras

parse arg digsL digsR . if \digsL.datatype('w') then digsL = 3 if \digsR.datatype('w') then digsR = digsL if digsL > digsR then digsR = digsL

loop dc = digsL to digsR

 say 'Middle' dc 'characters'
 loop nn = 1 to sl.words()
   val = sl.word(nn)
   say middleDigits(dc, val)
   end nn
 say
 end dc

return

-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ method middle3Digits(val) constant

 return middleDigits(3, val)

-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ method middleDigits(digitCt, val) constant

 text = val.right(15)':'
 even = digitCt // 2 == 0 -- odd or even?
 select
   when digitCt <= 0                       then text = 'digit selection size must be >= 1'
   when \val.datatype('w')                 then text = text 'is not a whole number'
   when val.abs().length < digitCt         then text = text 'has less than' digitCt 'digits'
   when \even & val.abs().length // 2 == 0 then text = text 'does not have an odd number of digits'
   when even  & val.abs().length // 2 \= 0 then text = text 'does not have an even number of digits'
   otherwise do
     val = val.abs()
     valL = val.length
     cutP = (valL - digitCt) % 2
     text = text val.substr(cutP + 1, digitCt)
     end
   catch NumberFormatException
     text = val 'is not numeric'
   end
 return text

</lang> Output:

Middle 3 characters
            123: 123
          12345: 234
        1234567: 345
      987654321: 654
          10001: 000
         -10001: 000
           -123: 123
           -100: 100
            100: 100
         -12345: 234
              1: has less than 3 digits
              2: has less than 3 digits
             -1: has less than 3 digits
            -10: has less than 3 digits
           2002: does not have an odd number of digits
          -2002: does not have an odd number of digits
              0: has less than 3 digits
            abc: is not a whole number
            1e3: is not a whole number
         -17e-3: is not a whole number
         4004.5: is not a whole number
       12345678: does not have an odd number of digits
     9876543210: does not have an odd number of digits

NewLISP

<lang NewLISP> (define (middle3 x)

   (if (even? (length x))
       (println "You entered " x ". I need an odd number of digits, not " (length x) ".")
       (if (< (length x) 3)
           (println "You entered " x ". Sorry, but I need 3 or more digits.")
           (println "The middle 3 digits of " x " are " ((- (/ (- (length x) 1) 2) 1) 3 (string (abs x))) ".")
       )
   )

)

(map middle3 lst) </lang> Output:

The middle 3 digits of 123 are 123.
The middle 3 digits of 12345 are 234.
The middle 3 digits of 1234567 are 345.
The middle 3 digits of 987654321 are 654.
The middle 3 digits of 10001 are 000.
The middle 3 digits of -10001 are 000.
The middle 3 digits of -123 are 123.
The middle 3 digits of -100 are 100.
The middle 3 digits of 100 are 100.
The middle 3 digits of -12345 are 234.
You entered 1. Sorry, but I need 3 or more digits.
You entered 2. Sorry, but I need 3 or more digits.
You entered -1. Sorry, but I need 3 or more digits.
You entered 10. I need an odd number of digits, not 2.
You entered 2002. I need an odd number of digits, not 4.
You entered -2002. I need an odd number of digits, not 4.
You entered 0. Sorry, but I need 3 or more digits.

Nim

<lang nim>import math

proc middleThreeDigits(i): auto =

 var s = $abs(i)
 if s.len < 3 or s.len mod 2 == 0:
   raise newException(ValueError, "Need odd and >= 3 digits")
 let mid = s.len div 2
 return s[mid-1..mid+1]

const passing = @[123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345] const failing = @[1, 2, -1, -10, 2002, -2002, 0]

for i in passing & failing:

 var answer = try: middleThreeDigits(i)
   except ValueError: getCurrentExceptionMsg()
 echo "middleThreeDigits(",i,") returned: ",answer</lang>

Output:

middleThreeDigits(123) returned: 123
middleThreeDigits(12345) returned: 234
middleThreeDigits(1234567) returned: 345
middleThreeDigits(987654321) returned: 654
middleThreeDigits(10001) returned: 000
middleThreeDigits(-10001) returned: 000
middleThreeDigits(-123) returned: 123
middleThreeDigits(-100) returned: 100
middleThreeDigits(100) returned: 100
middleThreeDigits(-12345) returned: 234
middleThreeDigits(1) returned: Need odd and >= 3 digits
middleThreeDigits(2) returned: Need odd and >= 3 digits
middleThreeDigits(-1) returned: Need odd and >= 3 digits
middleThreeDigits(-10) returned: Need odd and >= 3 digits
middleThreeDigits(2002) returned: Need odd and >= 3 digits
middleThreeDigits(-2002) returned: Need odd and >= 3 digits
middleThreeDigits(0) returned: Need odd and >= 3 digits

Objeck

<lang objeck> class Test {

 function : Main(args : String[]) ~ Nil {
   text := "123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0";
   ins := text->Split(",");
   each(i : ins) {
     in := ins[i]->Trim();
     IO.Console->Print(in)->Print(": ");
     in := (in->Size() > 0 & in->Get(0) = '-') ? in->SubString(1, in->Size() - 1) : in;
     IO.Console->PrintLine((in->Size() < 2 | in->Size() % 2 = 0) ? "Error" : in->SubString((in->Size() - 3) / 2, 3));
   };
 }

}</lang>

123: 123
12345: 234
1234567: 345
987654321: 654
10001: 000
-10001: 000
-123: 123
-100: 100
100: 100
-12345: 234
1: Error
2: Error
-1: Error
-10: Error
2002: Error
-2002: Error
0: Error

OCaml

<lang ocaml>let even x = (x land 1) <> 1

let middle_three_digits x =

 let s = string_of_int (abs x) in
 let n = String.length s in
 if n < 3 then failwith "need >= 3 digits" else
 if even n then failwith "need odd number of digits" else
 String.sub s (n / 2 - 1) 3

let passing = [123; 12345; 1234567; 987654321; 10001; -10001; -123; -100; 100; -12345] let failing = [1; 2; -1; -10; 2002; -2002; 0]

let print x =

 let res =
   try (middle_three_digits x)
   with Failure e -> "failure: " ^ e
 in
 Printf.printf "%d: %s\n" x res

let () =

 print_endline "Should pass:";
 List.iter print passing;
 print_endline "Should fail:";
 List.iter print failing;
</lang>
Output:
Should pass:
123: 123
12345: 234
1234567: 345
987654321: 654
10001: 000
-10001: 000
-123: 123
-100: 100
100: 100
-12345: 234

Should fail:
1: failure: need >= 3 digits
2: failure: need >= 3 digits
-1: failure: need >= 3 digits
-10: failure: need >= 3 digits
2002: failure: need odd number of digits
-2002: failure: need odd number of digits
0: failure: need >= 3 digits

Oforth

<lang Oforth>: middle3 | s sz |

  abs asString dup ->s size ->sz
  sz 3 <    ifTrue: [ "Too short" println return ]
  sz isEven ifTrue: [ "Not odd number of digits" println return ]
  sz 3 - 2 / 1+  dup 2 + s extract ;</lang>
Output:
[ 123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345] map(#middle3) println
[123, 234, 345, 654, 000, 000, 123, 100, 100, 234]

[ 1, 2, -1, -10, 2002, -2002, 0 ] apply(#middle3)
Too short
Too short
Too short
Too short
Not odd number of digits
Not odd number of digits
Too short

PARI/GP

Works with: PARI/GP version 2.6.0

<lang parigp>middle(n)=my(v=digits(n));if(#v>2&&#v%2,100*v[#v\2]+10*v[#v\2+1]+v[#v\2+2],"no middle 3 digits"); apply(middle,[123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0])</lang> Output:

%1 = [123, 234, 345, 654, 0, 0, 123, 100, 100, 234, "no middle 3 digits", "no middle 3 digits", "no middle 3 digits", "no middle 3 digits", "no middle 3 digits", "no middle 3 digits", "no middle 3 digits"]

If for some reason you want to see the leading digits, you can run <lang parigp>apply(n-> Strprintf("%03d", n), %)</lang>

For earlier versions digits can be defined as <lang parigp>digits(n)=eval(Vec(Str(n)))</lang> or more efficiently as <lang parigp>digits(n)=Vec(apply(n->n-48,Vectorsmall(Str(n))))</lang>

Pascal

Works with: Free Pascal

<lang pascal>program Midl3dig; {$IFDEF FPC}

 {$MODE Delphi} //result /integer => Int32 aka longInt etc..

{$ELSE}

 {$APPTYPE console} // Delphi

{$ENDIF} uses

 sysutils;   //IntToStr

function GetMid3dig(i:NativeInt):Ansistring; var

 n,l: NativeInt;

Begin

 setlength(result,0);
 //n = |i| jumpless abs
 n := i-((ORD(i>0)-1)AND (2*i));
 //calculate digitcount
 IF n > 0 then
   l := trunc(ln(n)/ln(10))+1
 else
   l := 1;
 if l<3 then Begin  write('got too few digits');  EXIT; end;
 If Not(ODD(l)) then Begin write('got even number of digits'); EXIT; end;
 result:= copy(IntToStr(n),l DIV 2,3);

end; const

 Test : array [0..16] of NativeInt =
   ( 123,12345,1234567,987654321,10001,-10001,
   -123,-100,100,-12345,1,2,-1,-10,2002,-2002,0);

var

 i,n : NativeInt;

Begin

 For i := low(Test) to High(Test) do
 Begin
   n := Test[i];
   writeln(n:9,': ',GetMid3dig(Test[i]));
 end;

end.</lang>

Output:
      123: 123
    12345: 234
  1234567: 345
987654321: 654
    10001: 000
   -10001: 000
     -123: 123
     -100: 100
      100: 100
   -12345: 234
        1: got too few digits
        2: got too few digits
       -1: got too few digits
      -10: got too few digits
     2002: got even number of digits
    -2002: got even number of digits
        0: got too few digits

Perl

<lang Perl>#!/usr/bin/perl use strict ; use warnings ;

sub middlethree {

  my $number = shift ;
  my $testnumber = abs $number ;
  my $error = "Middle 3 digits can't be shown" ;
  my $numberlength = length $testnumber ;
  if ( $numberlength < 3 ) {
     print "$error : $number too short!\n" ;
     return ;
  }
  if ( $numberlength % 2 == 0 ) {
     print "$error : even number of digits in $number!\n" ;
     return ;
  }
  my $middle = int ( $numberlength  / 2 ) ;
  print "Middle 3 digits of $number : " . substr( $testnumber , $middle - 1 , 3 ) . " !\n" ;
  return ;

}

my @numbers = ( 123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345 ,

     1, 2, -1, -10, 2002, -2002, 0 ) ;

map { middlethree( $_ ) } @numbers ; </lang>

Output:
Middle 3 digits of 123 : 123 !
Middle 3 digits of 12345 : 234 !
Middle 3 digits of 1234567 : 345 !
Middle 3 digits of 987654321 : 654 !
Middle 3 digits of 10001 : 000 !
Middle 3 digits of -10001 : 000 !
Middle 3 digits of -123 : 123 !
Middle 3 digits of -100 : 100 !
Middle 3 digits of 100 : 100 !
Middle 3 digits of -12345 : 234 !
Middle 3 digits can't be shown : 1 too short!
Middle 3 digits can't be shown : 2 too short!
Middle 3 digits can't be shown : -1 too short!
Middle 3 digits can't be shown : -10 too short!
Middle 3 digits can't be shown : even number of digits in 2002!
Middle 3 digits can't be shown : even number of digits in -2002!
Middle 3 digits can't be shown : 0 too short!

Phix

<lang Phix>procedure mid3(integer i)

   string s = sprintf("%d",abs(i))
   integer k = length(s)-3
   printf(1,"%10d: %s\n",{i,iff(k<0 or and_bits(k,1)?"error":s[k/2+1..k/2+3])})

end procedure

constant tests = {123,12345,1234567,987654321,10001,-10001,-123,-100,100,-12345,

                 1,2,-1,-10,2002,-2002,0}

for i=1 to length(tests) do

   mid3(tests[i])

end for</lang>

Output:
       123: 123
     12345: 234
   1234567: 345
 987654321: 654
     10001: 000
    -10001: 000
      -123: 123
      -100: 100
       100: 100
    -12345: 234
         1: error
         2: error
        -1: error
       -10: error
      2002: error
     -2002: error
         0: error

PHP

<lang PHP>// 32-bit builds of PHP: Integers can be from -2147483648 to 2147483647 // 64-bit builds of PHP: Integers can be from -9223372036854775808 to 9223372036854775807

function middlethree($integer) { $int = (int)str_replace('-',,$integer); $length = strlen($int);

if(is_int($int)) { if($length >= 3) { if($length % 2 == 1) { $middle = floor($length / 2) - 1; return substr($int,$middle, 3); } else { return 'The value must contain an odd amount of digits...'; } } else { return 'The value must contain at least three digits...'; } } else { return 'The value does not appear to be an integer...'; } }

$numbers = array(123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0);

foreach($numbers as $nums) { echo $nums.' : '.middlethree($nums). '
'; }</lang> Output:

123 : 123
12345 : 234
1234567 : 345
987654321 : 654
10001 : 000
-10001 : 000
-123 : 123
-100 : 100
100 : 100
-12345 : 234
1 : The value must contain at least three digits...
2 : The value must contain at least three digits...
-1 : The value must contain at least three digits...
-10 : The value must contain at least three digits...
2002 : The value must contain an odd amount of digits...
-2002 : The value must contain an odd amount of digits...
0 : The value must contain at least three digits...

PicoLisp

<lang PicoLisp>(de middle3digits (N)

  (let (Lst (chop (abs N))  Len (length Lst))
     (tab (10 -2 -30)
        N
        ":"
        (cond
           ((> 3 Len) "not enough digits")
           ((bit? 1 Len)
              (head 3 (nth Lst (/ Len 2))) )
           (T "even number of digits") ) ) ) )</lang>

Test: <lang PicoLisp>(mapc middle3digits

  (123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345
     1 2 -1 -10 2002 -2002 0 ) )</lang>

Output:

       123: 123
     12345: 234
   1234567: 345
 987654321: 654
     10001: 000
    -10001: 000
      -123: 123
      -100: 100
       100: 100
    -12345: 234
         1: not enough digits
         2: not enough digits
        -1: not enough digits
       -10: not enough digits
      2002: even number of digits
     -2002: even number of digits
         0: not enough digits

PL/I

<lang PL/I> middle: procedure options (main); /* 29 October 2013 */

  declare n fixed (15);
  declare s character (25) varying;
  declare in file input;
  open file (in) title ('/MIDDLE.DAT,type(text),recsize(100)');
  on endfile (in) stop;
  do forever;
     get file (in) list (n); put skip list (n);
     n = abs(n);
     s = trim(n);
     if length(s) < 3 then put list ('not possible');
     else  if mod(length(s), 2) = 0 then put list ('not possible');
     else
        do;
           do while (length(s) > 3);
              s = substr(s, 2, length(s)-2);
           end;
           put list ('The middle three digits are: ' || s);
        end;
  end;

end middle; </lang> Output:

               123      The middle three digits are: 123 
             12345      The middle three digits are: 234 
           1234567      The middle three digits are: 345 
         987654321      The middle three digits are: 654 
             10001      The middle three digits are: 000 
            -10001      The middle three digits are: 000 
              -123      The middle three digits are: 123 
              -100      The middle three digits are: 100 
               100      The middle three digits are: 100 
           -123451      not possible 
                 2      not possible 
                -1      not possible 
               -10      not possible 
              2002      not possible 
             -2002      not possible 
                 0      not possible

Plain English

<lang plainenglish>To run: Start up. Test 123. Test 12345. Test 1234567. Test 987654321. Test 10001. Test -10001. Test -123. Test -100. Test 100. Test -12345. Test 1. Test 2. Test -1. Test -10. Test 2002. Test -2002. Test 0. Wait for the escape key. Shut down.

To get the middle three digits of a number giving a string: Privatize the number. De-sign the number. Convert the number to the string. If the string's length is less than 3, put "Number has fewer than three digits" into the string; exit. If the string's length is even, put "Number has no middle" into the string; exit. Put the string's length divided by 2 into a midpoint number. Slap a substring on the string. Put the substring's first plus the midpoint minus 1 into the substring's first. Put the substring's first plus 2 into the substring's last. Put the substring into the string.

To test a number: Get the middle three digits of the number giving a string. Write "" then the number then " -> " then the string on the console.</lang>

Output:
123  ->  123
12345  ->  234
1234567  ->  345
987654321  ->  654
10001  ->  000
-10001  ->  000
-123  ->  123
-100  ->  100
100  ->  100
-12345  ->  234
1  ->  Number has fewer than three digits
2  ->  Number has fewer than three digits
-1  ->  Number has fewer than three digits
-10  ->  Number has fewer than three digits
2002  ->  Number has no middle
-2002  ->  Number has no middle
0  ->  Number has fewer than three digits

PowerShell

<lang powershell>function middle3($inp){

$str = [Math]::abs($inp)

$leng = "$str".length

if ($leng -lt 3){ Write-host $inp": [ERROR] too short." Return } if (($leng % 2) -eq 0){ Write-host $inp": [ERROR] even number of digits." } else { $trimmer = ($leng - 3) / 2 $ans = "$str".subString($trimmer,3)

Write-host $inp": $ans" } Return }

$sample = 123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0

foreach ($x in $sample){middle3 $x}</lang>

Output:
123:    123
12345:  234
1234567:        345
987654321:      654
10001:  000
-10001: 000
-123:   123
-100:   100
100:    100
-12345: 234
1:      [ERROR] too short.
2:      [ERROR] too short.
-1:     [ERROR] too short.
-10:    [ERROR] too short.
2002:   [ERROR] even number of digits.
-2002:  [ERROR] even number of digits.
0:      [ERROR] too short.

Prolog

Works with: SWI-Prolog version 6

<lang prolog> middle_3_digits(Number, [D1,D2,D3]) :-

   verify_middle_3_able(Number, Digits),    
   append(FrontDigits, [D1,D2,D3| BackDigits], Digits),
   same_length(FrontDigits, BackDigits).

verify_middle_3_able(Number, Digits) :-

   must_be(number, Number),
   AbsNumber is abs(Number),
   number_chars(AbsNumber, Digits),
   length(Digits, NumDigits),
   ( 3 > NumDigits         ->  domain_error('at least 3 digits',    Number)
   ; 0 is NumDigits mod 2  ->  domain_error('odd number of digits', Number)
   ; true
   ).

</lang>


Test code:

<lang prolog> test_correct :-

   TestCases = [123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345],
   foreach( ( member(TestCase, TestCases),
              middle_3_digits(TestCase, Result) ),
           format('Middle 3 digits of ~w ~30|: ~w~n', [TestCase, Result])
         ).

</lang>


Testing correct inputs:

?- test_correct.
Middle 3 digits of 123        : [1,2,3]
Middle 3 digits of 12345      : [2,3,4]
Middle 3 digits of 1234567    : [3,4,5]
Middle 3 digits of 987654321  : [6,5,4]
Middle 3 digits of 10001      : [0,0,0]
Middle 3 digits of -10001     : [0,0,0]
Middle 3 digits of -123       : [1,2,3]
Middle 3 digits of -100       : [1,0,0]
Middle 3 digits of 100        : [1,0,0]
Middle 3 digits of -12345     : [2,3,4]
true.

Errors

?- middle_3_digits(1, S).
ERROR: Domain error: `at least 3 digits' expected, found `1'
?- middle_3_digits(2, S).
ERROR: Domain error: `at least 3 digits' expected, found `2'
?- middle_3_digits(-1, S).
ERROR: Domain error: `at least 3 digits' expected, found `-1'
?- middle_3_digits(-10, S).
ERROR: Domain error: `at least 3 digits' expected, found `-10'
?- middle_3_digits(2002, S).
ERROR: Domain error: `odd number of digits' expected, found `2002'
?- middle_3_digits(-2002, S).
ERROR: Domain error: `odd number of digits' expected, found `-2002'
?- middle_3_digits(0, S).
ERROR: Domain error: `at least 3 digits' expected, found `0'

Python

Procedural

<lang python>>>> def middle_three_digits(i): s = str(abs(i)) length = len(s) assert length >= 3 and length % 2 == 1, "Need odd and >= 3 digits" mid = length // 2 return s[mid-1:mid+2]

>>> passing = [123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345] >>> failing = [1, 2, -1, -10, 2002, -2002, 0] >>> for x in passing + failing: try: answer = middle_three_digits(x) except AssertionError as error: answer = error print("middle_three_digits(%s) returned: %r" % (x, answer))


middle_three_digits(123) returned: '123' middle_three_digits(12345) returned: '234' middle_three_digits(1234567) returned: '345' middle_three_digits(987654321) returned: '654' middle_three_digits(10001) returned: '000' middle_three_digits(-10001) returned: '000' middle_three_digits(-123) returned: '123' middle_three_digits(-100) returned: '100' middle_three_digits(100) returned: '100' middle_three_digits(-12345) returned: '234' middle_three_digits(1) returned: AssertionError('Need odd and >= 3 digits',) middle_three_digits(2) returned: AssertionError('Need odd and >= 3 digits',) middle_three_digits(-1) returned: AssertionError('Need odd and >= 3 digits',) middle_three_digits(-10) returned: AssertionError('Need odd and >= 3 digits',) middle_three_digits(2002) returned: AssertionError('Need odd and >= 3 digits',) middle_three_digits(-2002) returned: AssertionError('Need odd and >= 3 digits',) middle_three_digits(0) returned: AssertionError('Need odd and >= 3 digits',) >>> </lang>

Composition of pure functions

Using a composable option type as an alternative to error handling:

Translation of: Haskell

<lang python>Middle 3 digits


  1. mid3digits :: Int -> Either String String

def mid3digits(n):

   Either the middle three digits,
      or an explanatory string.
   m = abs(n)
   s = str(m)
   return Left('Less than 3 digits') if (100 > m) else (
       Left('Even digit count') if even(len(s)) else Right(
           s[(len(s) - 3) // 2:][0:3]
       )
   )


  1. TEST ----------------------------------------------------

def main():

   Test
   def bracketed(x):
       return '(' + str(x) + ')'
   print(
       tabulated('Middle three digits, where defined:\n')(str)(
           either(bracketed)(str)
       )(mid3digits)([
           123, 12345, 1234567, 987654321, 10001, -10001, -123,
           -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0
       ])
   )


  1. GENERIC -------------------------------------------------
  1. Left :: a -> Either a b

def Left(x):

   Constructor for an empty Either (option type) value
      with an associated string.
   return {'type': 'Either', 'Right': None, 'Left': x}


  1. Right :: b -> Either a b

def Right(x):

   Constructor for a populated Either (option type) value
   return {'type': 'Either', 'Left': None, 'Right': x}


  1. compose (<<<) :: (b -> c) -> (a -> b) -> a -> c

def compose(g):

   Function composition.
   return lambda f: lambda x: g(f(x))


  1. either :: (a -> c) -> (b -> c) -> Either a b -> c

def either(fl):

   The application of fl to e if e is a Left value,
      or the application of fr to e if e is a Right value.
   return lambda fr: lambda e: fl(e['Left']) if (
       None is e['Right']
   ) else fr(e['Right'])


  1. even :: Int -> Bool

def even(x):

   Is x even ?
   return 0 == x % 2


  1. tabulated :: String -> (b -> String) -> (a -> b) -> [a] -> String

def tabulated(s):

   Heading -> x display function -> fx display function ->
               f -> value list -> tabular string.
   def go(xShow, fxShow, f, xs):
       w = max(map(compose(len)(str), xs))
       return s + '\n' + '\n'.join(
           xShow(x).rjust(w, ' ') + ' -> ' + fxShow(f(x)) for x in xs
       )
   return lambda xShow: lambda fxShow: lambda f: lambda xs: go(
       xShow, fxShow, f, xs
   )


if __name__ == '__main__':

   main()</lang>
Output:
Middle three digits, where defined:

      123 -> 123
    12345 -> 234
  1234567 -> 345
987654321 -> 654
    10001 -> 000
   -10001 -> 000
     -123 -> 123
     -100 -> 100
      100 -> 100
   -12345 -> 234
        1 -> (Less than 3 digits)
        2 -> (Less than 3 digits)
       -1 -> (Less than 3 digits)
      -10 -> (Less than 3 digits)
     2002 -> (Even digit count)
    -2002 -> (Even digit count)
        0 -> (Less than 3 digits)

Racket

<lang scheme>#lang racket (define (middle x)

 (cond
   [(negative? x) (middle (- x))]
   [(< x 100)     "error: number too small"]
   [else 
    (define s (number->string x))
    (define l (string-length s))
    (cond [(even? l) "error: number has even length"]
          [else (define i (quotient l 2)) 
                (substring s (- i 1) (+ i 2))])]))

(map middle (list 123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345)) (map middle (list 1 2 -1 -10 2002 -2002 0))</lang> The output: <lang scheme>'("123" "234" "345" "654" "000" "000" "123" "100" "100" "234") '("error: number too small" "error: number too small" "error: number too small" "error: number too small"

 "error: number has even length" "error: number has even length" "error: number too small")</lang>

Raku

(formerly Perl 6) <lang perl6>sub middle-three($n) {

   given $n.abs {
       when .chars < 3  { "$n is too short" }
       when .chars %% 2 { "$n has an even number of digits" }
       default          { "The three middle digits of $n are: ", .substr: (.chars - 3)/2, 3 }
   }

}

say middle-three($_) for <

   123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345
   1 2 -1 -10 2002 -2002 0

>;</lang>

Output:
The three middle digits of 123 are:  123
The three middle digits of 12345 are:  234
The three middle digits of 1234567 are:  345
The three middle digits of 987654321 are:  654
The three middle digits of 10001 are:  000
The three middle digits of -10001 are:  000
The three middle digits of -123 are:  123
The three middle digits of -100 are:  100
The three middle digits of 100 are:  100
The three middle digits of -12345 are:  234
1 is too short
2 is too short
-1 is too short
-10 is too short
2002 has an even number of digits
-2002 has an even number of digits
0 is too short

It is also possible to write a regular expression with a code assertion: <lang perl6>for [\~] ^10 { say "$_ => $()" if m/^^(\d+) <(\d**3)> (\d+) $$ <?{ $0.chars == $1.chars}> / }</lang>

Output:
01234 => 123
0123456 => 234
012345678 => 345

REXX

version 1

<lang rexx>/* REXX ***************************************************************

  • 03.02.2013 Walter Pachl
  • 19.04.2013 mid 3 is now a function returning the middle 3 digits
  • or an error indication
                                                                                                                                            • /

sl='123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345',

  '2 -1 -10 2002 -2002 0 abc 1e3 -17e-3'

Do While sl<> /* loop through test values */

 Parse Var sl s sl                    /* pick next value            */
 Say left(s,12) '->' mid3(s)          /* test it                    */
 End

Exit

mid3: Procedure Parse arg d /* take the argument */ Select /* first test for valid input */

 When datatype(d)<>'NUM'   Then  Return 'not a number'
 When pos('E',translate(d))>0 Then  Return 'not just digits'
 When length(abs(d))<3     Then  Return 'less than 3 digits'
 When length(abs(d))//2<>1 Then  Return 'not an odd number of digits'
 Otherwise Do                         /* input is ok                */
   dx=abs(d)                          /* get rid of optional sign   */
   ld=length(dx)                      /* length of digit string     */
   z=(ld-3)/2                         /* number of digits to cut    */
   res=substr(dx,z+1,3)               /* get middle 3 digits        */
   End
 End
 Return res</lang>

Output:

123          -> 123
12345        -> 234
1234567      -> 345
987654321    -> 654
10001        -> 000
-10001       -> 000
-123         -> 123
-100         -> 100
100          -> 100
-12345       -> 234
2            -> less than 3 digits
-1           -> less than 3 digits
-10          -> less than 3 digits
2002         -> not an odd number of digits
-2002        -> not an odd number of digits
0            -> less than 3 digits
abc          -> not a number
1e3          -> not just digits
-17e-3       -> not just digits

version 2

A premise:   12.3e2   is an integer   (regardless of how it's displayed).
So is the value of a   googol   and a  googolplex.

This REXX version is limited to numbers whose length is     100,000   decimal digits.
(The decimal digits limit is defined via the   numeric digits   statement in the first line of the subroutine/procedure.) <lang rexx>/*REXX program returns the three middle digits of a decimal number (or an error msg).*/ n= '123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345',

  '+123   0123    2     -1    -10    2002     -2002   0   abc   1e3   -17e-3   1234567.',
   1237654.00     1234567890123456789012345678901234567890123456789012345678901234567
      do j=1  for words(n);   #=word(n,j)       /* [↓]  format number for pretty output*/
      say 'middle 3 digits of'    right(#, max(15, length(#) ) )     "──►"     middle3(#)
      end   /*j*/

exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ middle3: procedure; parse arg x; numeric digits 1e6; er=' ***error*** '

        if  datatype(x,'N')  then x=abs(x)/1;  L=length(x)  /*use abs value; get length*/
        if \datatype(x,'W')  then return  er  "argument isn't an integer."
        if L<3               then return  er  "argument is less than three digits."
        if L//2==0           then return  er  "argument isn't an odd number of digits."
                                  return  substr(x, (L-3)%2+1, 3)</lang>

output

middle 3 digits of             123 ──► 123
middle 3 digits of           12345 ──► 234
middle 3 digits of         1234567 ──► 345
middle 3 digits of       987654321 ──► 654
middle 3 digits of           10001 ──► 000
middle 3 digits of          -10001 ──► 000
middle 3 digits of            -123 ──► 123
middle 3 digits of            -100 ──► 100
middle 3 digits of             100 ──► 100
middle 3 digits of          -12345 ──► 234
middle 3 digits of            +123 ──► 123
middle 3 digits of            0123 ──► 123
middle 3 digits of               2 ──►     ***error***  argument is less than three digits.
middle 3 digits of              -1 ──►     ***error***  argument is less than three digits.
middle 3 digits of             -10 ──►     ***error***  argument is less than three digits.
middle 3 digits of            2002 ──►     ***error***  argument isn't an odd number of digits.
middle 3 digits of           -2002 ──►     ***error***  argument isn't an odd number of digits.
middle 3 digits of               0 ──►     ***error***  argument is less than three digits.
middle 3 digits of             abc ──►     ***error***  argument isn't an integer.
middle 3 digits of             1e3 ──►     ***error***  argument isn't an odd number of digits.
middle 3 digits of          -17e-3 ──►     ***error***  argument isn't an integer.
middle 3 digits of        1234567. ──► 345
middle 3 digits of      1237654.00 ──► 376
middle 3 digits of 1234567890123456789012345678901234567890123456789012345678901234567 ──► 345

Ring

<lang ring> n = 1234567 middle(n)

func middle nr

    mnr = floor(len(string(nr))/2)
    lennr = len(string(nr))
    if lennr = 3 see "" + nr + nl
    but lennr < 3 see "Number must have at least three digits"
    but lennr%2=0 see "Number must have an odd number of digits"
    else cnr = substr(string(nr),mnr,3) see cnr + nl ok 

</lang>

Ruby

<lang ruby>def middle_three_digits(num)

 # minus sign doesn't factor into digit count,
 # and calling #abs acts as a duck-type assertion
 num = num.abs
 
 # convert to string and find length
 length = (str = num.to_s).length
 
 # check validity
 raise ArgumentError, "Number must have at least three digits" if length < 3
 raise ArgumentError, "Number must have an odd number of digits" if length.even?
 
 return str[length/2 - 1, 3].to_i

end</lang>

Testing program:

<lang ruby>samples = [

 123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345,
 1, 2, -1, -10, 2002, -2002, 0 

]

left_column_width = samples.map { |n| n.to_s.length }.max samples.each do |n|

 print "%#{left_column_width}d: " % n
 begin
   puts "%03d" % middle_three_digits(n)
 rescue ArgumentError => e
   puts e
 end

end</lang>

Output:
      123: 123
    12345: 234
  1234567: 345
987654321: 654
    10001: 000
   -10001: 000
     -123: 123
     -100: 100
      100: 100
   -12345: 234
        1: Number must have at least three digits
        2: Number must have at least three digits
       -1: Number must have at least three digits
      -10: Number must have at least three digits
     2002: Number must have an odd number of digits
    -2002: Number must have an odd number of digits
        0: Number must have at least three digits

Rust

<lang rust>fn middle_three_digits(x: i32) -> Result<String, String> {

   let s: String = x.abs().to_string();
   let len = s.len();
   if len < 3 {
       Err("Too short".into())
   } else if len % 2 == 0 {
       Err("Even number of digits".into())
   } else {
       Ok(s[len/2 - 1 .. len/2 + 2].to_owned())
   }

}

fn print_result(x: i32) {

   print!("middle_three_digits({}) returned: ", x);
   match middle_three_digits(x) {
       Ok(s) => println!("Success, {}", s),
       Err(s) => println!("Failure, {}", s)
   }

}

fn main() {

   let passing = [123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345];
   let failing = [1, 2, -1, -10, 2002, -2002, 0];
   for i in passing.iter() {
       print_result(*i);
   }
   for i in failing.iter() {
       print_result(*i);
   }

}</lang>

Output:
middle_three_digits(123) returned: Success, 123
middle_three_digits(12345) returned: Success, 234
middle_three_digits(1234567) returned: Success, 345
middle_three_digits(987654321) returned: Success, 654
middle_three_digits(10001) returned: Success, 000
middle_three_digits(-10001) returned: Success, 000
middle_three_digits(-123) returned: Success, 123
middle_three_digits(-100) returned: Success, 100
middle_three_digits(100) returned: Success, 100
middle_three_digits(-12345) returned: Success, 234
middle_three_digits(1) returned: Failure, Too short
middle_three_digits(2) returned: Failure, Too short
middle_three_digits(-1) returned: Failure, Too short
middle_three_digits(-10) returned: Failure, Too short
middle_three_digits(2002) returned: Failure, Even number of digits
middle_three_digits(-2002) returned: Failure, Even number of digits
middle_three_digits(0) returned: Failure, Too short

S-lang

Educational Notes:
1) Array-style string manipulations (e.g. as = as[[1:]] ) always use bytes,
   not UTF-8 characters.  As digits and '-' are all ASCII, all is copacetic.
2) The task doesn't require 64-bit integer support, but I added it, dependant
   on whether the S-Lang library compile supports them, which it generally
   does.  [Main exception would be the current downloadable/installable MS-Win
   version of the Jed editor.]   
3) S-Lang functions peel arguments off right-to-left, opposite of many
   languages.  To align the order with other solutions, I enclosed the
   parameters in a list.  One alternative would have been for m3() to call
   _stk_reverse(_NARGS), then pop each arg directly off the stack.  Or of
   course just list the numbers backwards.

<lang S-lang> define m3(i) {

   variable s = string(i), sabs = s, l;
   
   if (sabs[0] == '-')
       sabs = sabs1:;
   l = strlen(sabs);

   if (l < 3)
       print(sprintf("%s doesn't have enough digits", s));
   else if (l & 1) {
       variable st = (l-3) >> 1;
       print(sprintf("%13s: %s", s, sabsst:st+2));
   }
   else
       print(sprintf("%s has an even number of digits", s));

}

define middle_3(lst) {

   foreach (lst)
       m3( () );

}

middle_3( { 123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345,

  1. ifexists Int64_Type
        6644221335577ll, -11122588999ll,
  1. endif
        1, 2, -1, -10, 2002, -2002, 0 } );

</lang>

Output:

" 123: 123" " 12345: 234" " 1234567: 345" " 987654321: 654" " 10001: 000" " -10001: 000" " -123: 123" " -100: 100" " 100: 100" " -12345: 234" "6644221335577: 213" " -11122588999: 258" "1 doesn't have enough digits" "2 doesn't have enough digits" "-1 doesn't have enough digits" "-10 doesn't have enough digits" "2002 has an even number of digits" "-2002 has an even number of digits" "0 doesn't have enough digits"

Scala

<lang scala>/**

* Optionally return the middle three digits of an integer.
*
* @example List(123,12345,-789,1234,12) flatMap (middleThree(_)), returns: List(123, 234, 789)
*/

def middleThree( s:Int ) : Option[Int] = s.abs.toString match {

 case v if v.length % 2 == 0   => None   // Middle three is undefined for even lengths
 case v if v.length < 3        => None
 case v                        => 			
   val i = (v.length / 2) - 1
   Some( v.substring(i,i+3).toInt )

}


// A little test... val intVals = List(123,12345,1234567,987654321,10001,-10001,-123,-100,100,-12345,1,2,-1,-10,2002,-2002,0)

intVals map (middleThree(_)) map {

 case None => "No middle three" 
 case Some(v) => "%03d".format(v)  // Format the value, force leading zeroes 

} mkString("\n") </lang>

Output:
123
234
345
654
000
000
123
100
100
234
No middle three
No middle three
No middle three
No middle three
No middle three
No middle three
No middle three

Seed7

<lang seed7>$include "seed7_05.s7i";

const func string: middle3 (in integer: number) is func

 result
   var string: middle3 is "";
 begin
   middle3 := str(abs(number));
   if not odd(length(middle3)) or length(middle3) < 3 then
     middle3 := "error";
   else
     middle3 := middle3[succ((length(middle3) - 3) div 2) len 3];
   end if;
 end func;

const proc: main is func

 local
   var integer: number is 0;
   var string: mid3 is "";
 begin
   for number range [] (123, 12345, 1234567, 987654321, 10001, -10001, -123,
                        -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0) do
     writeln(number <& ": " <& middle3(number));
   end for;
 end func;</lang>
Output:
123: 123
12345: 234
1234567: 345
987654321: 654
10001: 000
-10001: 000
-123: 123
-100: 100
100: 100
-12345: 234
1: error
2: error
-1: error
-10: error
2002: error
-2002: error
0: error

SenseTalk

<lang sensetalk> set inputs to [123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345, 1, 2, -1, -10, 2002, -2002, 0]

repeat with each item of inputs put it into output put middle3digits of it into character 15 of output -- will autofill with "."s put output end repeat

to handle middle3digits of number put every occurrence of <digit> in number into digits if the number of items in digits is less than 3 then return "Error: too few digits" if the number of items in digits is an even number then return "Error: even number of digits" repeat while the number of items in digits is greater than 3 delete the first item of digits delete the last item of digits end repeat return digits joined by empty end middle3digits </lang> Output:

123...........123
12345.........234
1234567.......345
987654321.....654
10001.........000
-10001........000
-123..........123
-100..........100
100...........100
-12345........234
1.............Error: too few digits
2.............Error: too few digits
-1............Error: too few digits
-10...........Error: too few digits
2002..........Error: even number of digits
-2002.........Error: even number of digits
0.............Error: too few digits

Sidef

Translation of: Raku

<lang ruby>func middle_three(n) {

 var l = n.len;
 if (l < 3) {
   "#{n} is too short"
 } elsif (l.is_even) {
   "#{n} has an even number of digits"
 } else {
   "The three middle digits of #{n} are: " + n.digits.ft(l-3 / 2, l/2 + 1).join
 }

}

var nums = %n(

   123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345
   1 2 -1 -10 2002 -2002 0

); nums.each { say middle_three(_) };</lang>

Output:
The three middle digits of 123 are: 123
The three middle digits of 12345 are: 234
The three middle digits of 1234567 are: 345
The three middle digits of 987654321 are: 654
The three middle digits of 10001 are: 000
The three middle digits of -10001 are: 000
The three middle digits of -123 are: 123
The three middle digits of -100 are: 100
The three middle digits of 100 are: 100
The three middle digits of -12345 are: 234
1 is too short
2 is too short
-1 is too short
-10 is too short
2002 has an even number of digits
-2002 has an even number of digits
0 is too short

SQL

<lang sql>;WITH DATA

    AS (SELECT CAST(ABS(NUMBER) AS NVARCHAR(MAX))      charNum, 
               NUMBER, 
               LEN(CAST(ABS(NUMBER) AS NVARCHAR(MAX))) LcharNum 
        FROM   TABLE1) 

SELECT CASE

        WHEN ( LCHARNUM >= 3 
               AND LCHARNUM % 2 = 1 ) THEN SUBSTRING(CHARNUM, LCHARNUM / 2, 3) 
        ELSE 'Error!' 
      END    Output, 
      NUMBER Input 

FROM DATA </lang>

| OUTPUT |     INPUT |
|--------|-----------|
|    123 |       123 |
|    234 |     12345 |
|    345 |   1234567 |
|    654 | 987654321 |
|    000 |     10001 |
|    000 |    -10001 |
|    123 |      -123 |
|    100 |      -100 |
|    100 |       100 |
|    234 |    -12345 |
| OUTPUT | INPUT |
|--------|-------|
| Error! |     1 |
| Error! |     2 |
| Error! |    -1 |
| Error! |   -10 |
| Error! |  2002 |
| Error! | -2002 |
| Error! |     0 |
		

Swift

<lang swift>var num:Int = \\enter your number here if num<0{num = -num} var numArray:[Int]=[] while num>0{ var temp:Int=num%10 numArray.append(temp) num=num/10 } var i:Int=numArray.count if i<3||i%2==0{ print("Invalid Input") } else{ i=i/2 print("\(numArray[i+1]),\(numArray[i]),\(numArray[i-1])") }</lang>

      123: 123
    12345: 234
  1234567: 345
987654321: 654
    10001: 000
   -10001: 000
     -123: 123
     -100: 100
      100: 100
   -12345: 234
        1: Invalid Input
        2: Invalid Input
       -1: Invalid Input
      -10: Invalid Input
     2002: Invalid Input
    -2002: Invalid Input
        0: Invalid Input

Tcl

<lang tcl>proc middleThree n {

   if {$n < 0} {

set n [expr {-$n}]

   }
   set idx [expr {[string length $n] - 2}]
   if {$idx % 2 == 0} {

error "no middle three digits: input is of even length"

   }
   if {$idx < 1} {

error "no middle three digits: insufficient digits"

   }
   set idx [expr {$idx / 2}]
   string range $n $idx [expr {$idx+2}]

}</lang> Demonstrating: <lang tcl>foreach n {

   123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345
   1 2 -1 -10 2002 -2002 0

} {

   if {[catch {

set mid [middleThree $n]

   } msg]} then {

puts "error for ${n}: $msg"

   } else {

puts "found for ${n}: $mid"

   }

}</lang>

Output:
found for 123: 123
found for 12345: 234
found for 1234567: 345
found for 987654321: 654
found for 10001: 000
found for -10001: 000
found for -123: 123
found for -100: 100
found for 100: 100
found for -12345: 234
error for 1: no middle three digits: insufficient digits
error for 2: no middle three digits: insufficient digits
error for -1: no middle three digits: insufficient digits
error for -10: no middle three digits: input is of even length
error for 2002: no middle three digits: input is of even length
error for -2002: no middle three digits: input is of even length
error for 0: no middle three digits: insufficient digits

UNIX Shell

Works with: Bourne Again Shell
Works with: Korn Shell version 93
Works with: Z Shell

<lang bash>function middle3digits {

 typeset -i n="${1#-}"
 typeset -i l=${#n}
 if (( l < 3 )); then
   echo >&2 "$1 has less than 3 digits"
   return 1
 elif (( l % 2 == 0 )); then
   echo >&2 "$1 has an even number of digits"
   return 1
 else
   echo ${n:$((l/2-1)):3}
   return 0
 fi

}

  1. test

testdata=(123 12345 1234567 987654321 10001 -10001 -123 -100 100 -12345 1 2 -1

         -10 2002 -2002 0)

for n in ${testdata[@]}; do

 printf "%10d: " $n
 middle3digits "$n"

done</lang>

Output:
       123: 123
     12345: 234
   1234567: 345
 987654321: 654
     10001: 000
    -10001: 000
      -123: 123
      -100: 100
       100: 100
    -12345: 234
         1: 1 has less than 3 digits
         2: 2 has less than 3 digits
        -1: -1 has less than 3 digits
       -10: -10 has less than 3 digits
      2002: 2002 has an even number of digits
     -2002: -2002 has an even number of digits
         0: 0 has less than 3 digits

VBA

<lang vb> Option Explicit

Sub Main_Middle_three_digits() Dim Numbers, i&

   Numbers = Array(123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, _
   100, -12345, 1, 2, -1, -10, 2002, -2002, 0)
   For i = 0 To 16
       Debug.Print Numbers(i) & " Return : " & Middle3digits(CStr(Numbers(i)))
   Next

End Sub

Function Middle3digits(strNb As String) As String

   If Left(strNb, 1) = "-" Then strNb = Right(strNb, Len(strNb) - 1)
   If Len(strNb) < 3 Then
       Middle3digits = "Error ! Number of digits must be >= 3"
   ElseIf Len(strNb) Mod 2 = 0 Then
       Middle3digits = "Error ! Number of digits must be odd"
   Else
       Middle3digits = Mid(strNb, 1 + (Len(strNb) - 3) / 2, 3)
   End If

End Function </lang>

Output:
123 Return : 123
12345 Return : 234
1234567 Return : 345
987654321 Return : 654
10001 Return : 000
-10001 Return : 000
-123 Return : 123
-100 Return : 100
100 Return : 100
-12345 Return : 234
1 Return : Error ! Number of digits must be >= 3
2 Return : Error ! Number of digits must be >= 3
-1 Return : Error ! Number of digits must be >= 3
-10 Return : Error ! Number of digits must be >= 3
2002 Return : Error ! Number of digits must be odd
-2002 Return : Error ! Number of digits must be odd
0 Return : Error ! Number of digits must be >= 3

VBScript

<lang vb>'http://rosettacode.org/wiki/Middle_three_digits

Function mid3n(n) 'Remove the number's sign. n = CStr(Abs(n)) If Len(n) < 3 Or Len(n) Mod 2 = 0 Then mid3n = "Invalid: Either the length of n < 3 or an even number." ElseIf Round(Len(n)/2) > Len(n)/2 Then mid3n = Mid(n,Round(Len(n)/2)-1,3) Else mid3n = Mid(n,Round(Len(n)/2),3) End If End Function

'Calling the function. arrn = Array(123,12345,1234567,987654321,10001,-10001,-123,-100,100,-12345,_ 1,2,-1,-10,2002,-2002,0) For Each n In arrn WScript.StdOut.Write n & ": " & mid3n(n) WScript.StdOut.WriteLine Next</lang>

Output:
123: 123
12345: 234
1234567: 345
987654321: 654
10001: 000
-10001: 000
-123: 123
-100: 100
100: 100
-12345: 234
1: Invalid: Either the length of n < 3 or an even number.
2: Invalid: Either the length of n < 3 or an even number.
-1: Invalid: Either the length of n < 3 or an even number.
-10: Invalid: Either the length of n < 3 or an even number.
2002: Invalid: Either the length of n < 3 or an even number.
-2002: Invalid: Either the length of n < 3 or an even number.
0: Invalid: Either the length of n < 3 or an even number.

Vedit macro language

<lang vedit>do {

   #1 = Get_Num("Enter a number, or 0 to stop: ", STATLINE)
   Ins_Text("Input: ") Num_Ins(#1, COUNT, 10)
   Call("MIDDLE_3_DIGITS")
   Ins_Text("  Result: ") Reg_Ins(10) Ins_Newline
   Update()

} while (#1); Return

// Find middle 3 digits of a number // in: #1 = numeric value // out: @10 = the result, or error text //

MIDDLE_3_DIGITS:

Buf_Switch(Buf_Free) Num_Ins(abs(#1), LEFT+NOCR) // the input value as string

  1. 2 = Cur_Col-1 // #2 = number of digits

if (#2 < 3) {

   Reg_Set(10, "Too few digits!")

} else {

   if ((#2 & 1) == 0) {

Reg_Set(10, "Not odd number of digits!")

   } else {

Goto_Pos((#2-3)/2) Reg_Copy_Block(10, Cur_Pos, Cur_Pos+3)

   }

} Buf_Quit(OK) Return </lang>

Output:

Input:        123  Result: 123
Input:      12345  Result: 234
Input:    1234567  Result: 345
Input:  987654321  Result: 654
Input:      10001  Result: 000
Input:     -10001  Result: 000
Input:       -123  Result: 123
Input:       -100  Result: 100
Input:        100  Result: 100
Input:     -12345  Result: 234
Input:          1  Result: Too few digits!
Input:          2  Result: Too few digits!
Input:         -1  Result: Too few digits!
Input:        -10  Result: Too few digits!
Input:       2002  Result: Not odd number of digits!
Input:      -2002  Result: Not odd number of digits!
Input:          0  Result: Too few digits! 

Wart

<lang wart>def (mid3 n)

 withs (digits  (with outstring  # itoa
                  (pr abs.n))
        max  len.digits
        mid  (int max/2))
   if (and odd?.max (max >= 3))
     (digits mid-1 mid+2)</lang>

Output

mid3.123
=> 123
mid3.12345
=> 234
mid3.1234567
=> 345
mid3.987654321
=> 654
mid3.10001
=> 000
mid3 -10001
=> 000
(mid3 -123)
=> 123
(mid3 -100)
=> 100
(mid3 100)
=> 100
(mid3 -12345)
=> 234

# Errors
mid3.1
=> nil
mid3.2
=> nil
mid3 -1
=> nil
mid3 -10
=> nil
mid3 2002
=> nil
mid3 -2002
=> nil
(mid3 0)
=> nil

Wren

Library: Wren-fmt

<lang ecmascript>import "/fmt" for Fmt

var middle3 = Fn.new { |n|

   if (n < 0) n = -n
   var s = "%(n)"
   var c = s.count
   if (c < 3) return "Minimum is 3 digits, only has %(c)."
   if (c%2 == 0) return "Number of digits must be odd, %(c) is even."
   if (c == 3) return s
   var d = (c - 3)/2
   return s[d..d+2]

}

var a = [123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345,

   1, 2, -1, -10, 2002, -2002, 0]

for (e in a) {

   System.print("%(Fmt.s(9, e)) -> %(middle3.call(e))")

}</lang>

Output:
      123 -> 123
    12345 -> 234
  1234567 -> 345
987654321 -> 654
    10001 -> 000
   -10001 -> 000
     -123 -> 123
     -100 -> 100
      100 -> 100
   -12345 -> 234
        1 -> Minimum is 3 digits, only has 1.
        2 -> Minimum is 3 digits, only has 1.
       -1 -> Minimum is 3 digits, only has 1.
      -10 -> Minimum is 3 digits, only has 2.
     2002 -> Number of digits must be odd, 4 is even.
    -2002 -> Number of digits must be odd, 4 is even.
        0 -> Minimum is 3 digits, only has 1.

XPL0

<lang XPL0>include c:\cxpl\stdlib;

func Mid3Digits(I); \Return the middle three digits of I int I; int Len, Mid; char S(10); [ItoA(abs(I), S); Len:= StrLen(S); if Len<3 or (Len&1)=0 then return "Must be 3, 5, 7 or 9 digits"; Mid:= Len/2; S:= S + Mid - 1; S(2):= S(2) ! $80; \terminate string return S; \WARNING: very temporary ];

int Passing, Failing, X; [Passing:= [123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345];

Failing:= [1, 2, -1, -10, 2002, -2002, 0];     \WARNING: nasty trick

for X:= 0 to 16 do

   [Text(0, "Middle three digits of ");  IntOut(0, Passing(X));
    Text(0, " returned: ");
    Text(0, Mid3Digits(Passing(X)));  CrLf(0);
   ];

]</lang>

Output:
Middle three digits of 123 returned: 123
Middle three digits of 12345 returned: 234
Middle three digits of 1234567 returned: 345
Middle three digits of 987654321 returned: 654
Middle three digits of 10001 returned: 000
Middle three digits of -10001 returned: 000
Middle three digits of -123 returned: 123
Middle three digits of -100 returned: 100
Middle three digits of 100 returned: 100
Middle three digits of -12345 returned: 234
Middle three digits of 1 returned: Must be 3, 5, 7 or 9 digits
Middle three digits of 2 returned: Must be 3, 5, 7 or 9 digits
Middle three digits of -1 returned: Must be 3, 5, 7 or 9 digits
Middle three digits of -10 returned: Must be 3, 5, 7 or 9 digits
Middle three digits of 2002 returned: Must be 3, 5, 7 or 9 digits
Middle three digits of -2002 returned: Must be 3, 5, 7 or 9 digits
Middle three digits of 0 returned: Must be 3, 5, 7 or 9 digits

zkl

<lang zkl>fcn middle(ns){

  ns.apply("toString").apply('-("-"))
  .apply(fcn(n){nl:=n.len(); 
     if(nl<3 or nl.isEven) return(False);
     n[(nl-3)/2,3] : "%03d".fmt(_)
  })

} middle(T(123,12345,1234567,987654321,10001,-10001,-123,-100,100,-12345)).println() middle(T(1, 2, -1, -10, 2002, -2002, 0)).println();</lang>

Output:
L("123","234","345","654","000","000","123","100","100","234")
L(False,False,False,False,False,False,False)

Algorithm is convert each number into a string, remove any "-", reject strings less than 3 characters or are even in length, return middle three characters of remainder.