Even or odd

Even or odd
You are encouraged to solve this task according to the task description, using any language you may know.

Task

Test whether an integer is even or odd.

There is more than one way to solve this task:

• Use the even and odd predicates, if the language provides them.
• Check the least significant digit. With binary integers, i bitwise-and 1 equals 0 iff i is even, or equals 1 iff i is odd.
• Divide i by 2. The remainder equals 0 iff i is even. The remainder equals +1 or -1 iff i is odd.
• Use modular congruences:
  • i ≡ 0 (mod 2) iff i is even.
  • i ≡ 1 (mod 2) iff i is odd.

0815

}:s:|=<:2:x~#:e:=/~%~<:20:~$=<:73:x<:69:~$~$~<:20:~$=^:o:<:65:
x<:76:=$=$~$<:6E:~$<:a:~$^:s:}:o:<:6F:x<:64:x~$~$$<:a:~$^:s:

11l

F is_even(i)
   R i % 2 == 0

F is_odd(i)
   R i % 2 == 1

6502 Assembly

        .lf  evenodd6502.lst
        .cr  6502
        .tf  evenodd6502.obj,ap1
;------------------------------------------------------
; Even or Odd for the 6502 by barrym95838 2014.12.10
; Thanks to sbprojects.com for a very nice assembler!
; The target for this assembly is an Apple II with
;   mixed-case output capabilities.  Apple IIs like to
;   work in '+128' ascii, and this version is tailored
;   to that preference.
; Tested and verified on AppleWin 1.20.0.0
;------------------------------------------------------
; Constant Section
;
CharIn   =   $fd0c      ;Specific to the Apple II
CharOut  =   $fded      ;Specific to the Apple II
;------------------------------------------------------
; The main program
;
main    ldy  #sIntro-sbase
        jsr  puts       ;Print Intro
loop    jsr  CharIn     ;Get a char from stdin
        cmp  #$83       ;Ctrl-C?
        beq  done       ;  yes:  end program
        jsr  CharOut    ;Echo char
        ldy  #sOdd-sbase ;Pre-load odd string
        lsr             ;LSB of char to carry flag
        bcs  isodd
        ldy  #sEven-sbase
isodd   jsr  puts       ;Print appropriate response
        beq  loop       ;Always taken
; Output NUL-terminated string @ offset Y
;
puts    lda  sbase,y    ;Get string char
        beq  done       ;Done if NUL
        jsr  CharOut    ;Output the char
        iny             ;Point to next char
        bne  puts       ;Loop up to 255 times
done    rts             ;Return to caller
;------------------------------------------------------
; String Constants (in '+128' ascii, Apple II style)
;
sbase:                  ;String base address
sIntro  .az     -"Hit any key (Ctrl-C to quit):",-#13
sEven   .az     -" is even.",-#13
sOdd    .az     -" is odd.",-#13
;------------------------------------------------------
        .en

68000 Assembly

Non-Destructive

BTST D0,#1
BNE isOdd
;else, is even.

Destructive

AND.B D0,#1
BNE isOdd
;else, is even.

ROR.B D0,#1
BCS isOdd
;else, is even.

ROXR.B D0,#1
BCS isOdd
;else, is even.

LSR.B D0,#1
BCS isOdd
;else, is even.

ASR.B D0,#1
BCS isOdd
;else, is even.

You can also use BCLR,BSET, and BCHG in the same way you use BTST, as all of them copy the affected bit to the zero flag. BCLR,BSET, and BCHG will change the value of that bit after the test, so keep that in mind.

8080 Assembly

The instruction that's doing all the work here is rar, which is a bitwise right rotate of the accumulator through the carry flag. That leaves the low bit in the carry flag, which will be set if odd and clear if even.

CMDLIN:	equ	80h		; Location of CP/M command line argument
puts:	equ	9h		; Syscall to print a string
	;;;	Check if number given on command line is even or odd
	org	100h
	lxi	h,CMDLIN	; Find length of argument
	mov	a,m
	add	l		; Look up last character (digit)
	mov	l,a
	mov	a,m		; Retrieve low digit
	rar			; Rotate low bit into carry flag
	mvi	c,puts		; Prepare to print string
	lxi	d,odd		; If carry is set, then the number is odd
	jc	5		; So print 'odd'
	lxi	d,even		; Otherwise, the number is even
	jmp 	5		; So print 'even'
even:	db	'Even$'		; Strings
odd:	db	'Odd$'

Output:

A>evenodd 0
Even
A>evenodd 1
Odd
A>evenodd 2
Even
A>evenodd 3141592653
Odd
A>

8086 Assembly

Non-Destructive

test ax,1
jne isOdd
;else, is even

Destructive

and ax,1
jne isOdd
;else, is even

ror ax,1
jc isOdd
;else, is even

rcr ax,1
jc isOdd
;else, is even

sar ax,1
jc isOdd
;else, is even

shr ax,1
jc isOdd
;else, is even

The DIV instruction can also work, but using DIV to divide by 2 is a waste of time, since the shift and rotate commands above do it faster.

8th

The 'mod' method also works, but the bit method is fastest.

: odd? \ n -- boolean
    dup 1 n:band 1 n:= ;
: even? \ n -- boolean
    odd? not ;

This could be shortened to:

: even? \ n -- f
  1 n:band not ;
: odd? \ n -- f
  even? not ;

AArch64 Assembly

Works with: as version Raspberry Pi 3B version Buster 64 bits

/* ARM assembly AARCH64 Raspberry PI 3B and android arm 64 bits*/
/*  program oddEven64.s   */

/*******************************************/
/* Constantes file                         */
/*******************************************/
/* for this file see task include a file in language AArch64 assembly*/
.include "../includeConstantesARM64.inc"

/*********************************/
/* Initialized data              */
/*********************************/
.data
sMessResultOdd:        .asciz " @ is odd (impair) \n"
sMessResultEven:       .asciz " @ is even (pair)  \n"
szCarriageReturn:      .asciz "\n"

/*********************************/
/* UnInitialized data            */
/*********************************/
.bss
sZoneConv:        .skip 24
/*********************************/
/*  code section                 */
/*********************************/
.text
.global main
main:                                 //entry of program

    mov x0,#5
    bl testOddEven
    mov x0,#12
    bl testOddEven
    mov x0,#2021
    bl testOddEven
100:                                  //standard end of the program
    mov x0, #0                        //return code
    mov x8, #EXIT                     //request to exit program
    svc #0                            //perform the system call

qAdrszCarriageReturn:     .quad szCarriageReturn
qAdrsMessResultOdd:       .quad sMessResultOdd
qAdrsMessResultEven:      .quad sMessResultEven
qAdrsZoneConv:            .quad sZoneConv
/***************************************************/
/*     test if number is odd or even               */
/***************************************************/
// x0 contains à number
testOddEven:
    stp x1,lr,[sp,-16]!       // save  registres
    tst x0,#1                   //test bit 0 to one
    beq 1f                      //if result are all zéro, go to even
    ldr x1,qAdrsZoneConv        //else display odd message
    bl conversion10             //call decimal conversion
    ldr x0,qAdrsMessResultOdd
    ldr x1,qAdrsZoneConv        //insert value conversion in message
    bl strInsertAtCharInc
    bl affichageMess
    b 100f
1:
    ldr x1,qAdrsZoneConv
    bl conversion10             //call decimal conversion
    ldr x0,qAdrsMessResultEven
    ldr x1,qAdrsZoneConv        //insert conversion in message
    bl strInsertAtCharInc
    bl affichageMess
100:
    ldp x1,lr,[sp],16         // restaur des  2 registres
    ret
/********************************************************/
/*        File Include fonctions                        */
/********************************************************/
/* for this file see task include a file in language AArch64 assembly */
.include "../includeARM64.inc"

Output:

 5 is odd (impair)
 12 is even (pair)
 2021 is odd (impair)

ABAP

cl_demo_output=>display(
  VALUE string_table(
    FOR i = -5 WHILE i < 6 (
      COND string(
        LET r = i MOD 2 IN
        WHEN r = 0 THEN |{ i } is even|
        ELSE |{ i } is odd|
      )
    )
  )
).

Output:

Table 
-5 is odd 
-4 is even 
-3 is odd 
-2 is even 
-1 is odd 
0 is even 
1 is odd 
2 is even 
3 is odd 
4 is even 
5 is odd 

Action!

PROC OddByAnd(INT v)
  IF (v&1)=0 THEN
    Print(" even")
  ELSE
    Print(" odd ")
  FI
RETURN

PROC OddByMod(INT v)
  ;MOD doesn't work properly for negative numbers in Action!
  IF v<0 THEN
    v=-v
  FI
  IF v MOD 2=0 THEN
    Print(" even")
  ELSE
    Print(" odd ")
  FI
RETURN

PROC OddByDiv(INT v)
  INT d
  d=(v/2)*2
  IF v=d THEN
    Print(" even")
  ELSE
    Print(" odd ")
  FI
RETURN

PROC Main()
  INT i

  FOR i=-4 TO 4
  DO
    PrintF("%I is",i)
    OddByAnd(i)
    OddByMod(i)
    OddByDiv(i)
    PutE()
  OD
RETURN

Output:

Screenshot from Atari 8-bit computer

-4 is even even even
-3 is odd  odd  odd
-2 is even even even
-1 is odd  odd  odd
0 is even even even
1 is odd  odd  odd
2 is even even even
3 is odd  odd  odd
4 is even even even

Ada

-- Ada has bitwise operators in package Interfaces,
-- but they work with Interfaces.Unsigned_*** types only.
-- Use rem or mod for Integer types, and let the compiler
-- optimize it.
declare
   N : Integer := 5;
begin
   if N rem 2 = 0 then
      Put_Line ("Even number");
   elseif N rem 2 /= 0 then
      Put_Line ("Odd number");
   else
      Put_Line ("Something went really wrong!");
   end if;
end;

Agda

module EvenOrOdd where

open import Data.Bool using (Bool; false; true)
open import Data.Nat using (ℕ; zero; suc)

even : ℕ → Bool
odd  : ℕ → Bool

even zero    = true
even (suc n) = odd n

odd zero    = false
odd (suc n) = even n

Aime

if (x & 1) {
    # x is odd
} else {
    # x is even
}

ALGOL 68

Works with: ALGOL 68G version Any - tested with release 2.8.win32

# Algol 68 has a standard operator: ODD which returns TRUE if its integer  #
# operand is odd and FALSE if it is even                                   #
# E.g.:                                                                    #

INT n;
print( ( "Enter an integer: " ) );
read( ( n ) );
print( ( whole( n, 0 ), " is ", IF ODD n THEN "odd" ELSE "even" FI, newline ) )

ALGOL-M

Because ALGOL-M lacks a built-in MOD operator or function and does not support bitwise operations on integers, the test is a bit cumbersome, but gets the job done.

BEGIN

% RETURN 1 IF EVEN, OTHERWISE 0 %
INTEGER FUNCTION EVEN(I);
INTEGER I;
BEGIN
  EVEN := 1 - (I - 2 * (I / 2));
END;

% TEST THE ROUTINE %
INTEGER K;
FOR K := 1 STEP 3 UNTIL 10 DO
  WRITE(K," IS ", IF EVEN(K) = 1 THEN "EVEN" ELSE "ODD");

END

Output:

    1 IS ODD
    4 IS EVEN
    7 IS ODD
   10 IS EVEN

An alternate (but mathematically equivalent) coding, demonstrating the use of a conditional test as part of an assignment statement:

% RETURN 1 IF EVEN, OTHERWISE 0 %
INTEGER FUNCTION EVEN(I);
INTEGER I;
BEGIN
  EVEN := (IF I = 2 * (I / 2) THEN 1 ELSE 0);
END;

ALGOL W

begin
    % the Algol W standard procedure odd returns true if its integer  %
    % parameter is odd, false if it is even                           %
    for i := 1, 1702, 23, -26
    do begin
        write( i, " is ", if odd( i ) then "odd" else "even" )
    end for_i
end.

Output:

             1   is odd
          1702   is even
            23   is odd
           -26   is even

AntLang

odd: {x mod 2}
even: {1 - x mod 2}

APL

The easiest way is probably to use modulo.

      2|28
0
      2|37
1

So you can write a user-defined operator.

     odd ← 2∘|

AppleScript

set L to {3, 2, 1, 0, -1, -2, -3}

set evens to {}
set odds to {}

repeat with x in L
    if (x mod 2 = 0) then
        set the end of evens to x's contents
    else
        set the end of odds to x's contents
    end if
end repeat

return {even:evens, odd:odds}

Output:

{even:{2, 0, -2}, odd:{3, 1, -1, -3}}

Or, packaging reusable functions that can serve as arguments to filter, partition etc (deriving even from mod, and odd from even):

----------------------- EVEN OR ODD ------------------------

-- even :: Int -> Bool
on even(n)
    0 = n mod 2
end even

-- odd :: Int -> Bool
on odd(n)
    not even(n)
end odd


--------------------------- TEST ---------------------------
on run
    
    partition(odd, enumFromTo(-6, 6))
    
    --> {{-5, -3, -1, 1, 3, 5}, {-6, -4, -2, 0, 2, 4, 6}}
end run


-------------------- GENERICS FOR TEST ---------------------

-- enumFromTo :: Int -> Int -> [Int]
on enumFromTo(m, n)
    if m ≤ n then
        set lst to {}
        repeat with i from m to n
            set end of lst to i
        end repeat
        lst
    else
        {}
    end if
end enumFromTo



-- partition :: (a -> Bool) -> [a] -> ([a], [a])
on partition(p, xs)
    tell mReturn(p)
        set {ys, zs} to {{}, {}}
        repeat with x in xs
            set v to contents of x
            if |λ|(v) then
                set end of ys to v
            else
                set end of zs to v
            end if
        end repeat
    end tell
    {ys, zs}
end partition


-- 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

Output:

{{-5, -3, -1, 1, 3, 5}, {-6, -4, -2, 0, 2, 4, 6}}

Arendelle

( input , "Please enter a number: " )

{ @input % 2 = 0 ,

	"| @input | is even!"
,
	"| @input | is odd!"
}

ARM Assembly

Works with: as version Raspberry Pi

/* ARM assembly Raspberry PI  or android 32 bits */
/*  program oddEven.s   */

/* REMARK 1 : this program use routines in a include file
   see task Include a file language arm assembly
   for the routine affichageMess conversion10
   see at end of this program the instruction include */
/* for constantes see task include a file in arm assembly */
/************************************/
/* Constantes                       */
/************************************/
.include "../constantes.inc"

/*********************************/
/* Initialized data              */
/*********************************/
.data
sMessResultOdd:        .asciz " @  is odd (impair) \n"
sMessResultEven:       .asciz " @  is even (pair)  \n"
szCarriageReturn:   .asciz "\n"

/*********************************/
/* UnInitialized data            */
/*********************************/
.bss
sZoneConv:        .skip 24
/*********************************/
/*  code section                 */
/*********************************/
.text
.global main
main:                                 @ entry of program

    mov r0,#5
    bl testOddEven
    mov r0,#12
    bl testOddEven
    mov r0,#2021
    bl testOddEven
100:                                  @ standard end of the program
    mov r0, #0                        @ return code
    mov r7, #EXIT                     @ request to exit program
    svc #0                            @ perform the system call

iAdrszCarriageReturn:     .int szCarriageReturn
iAdrsMessResultOdd:       .int sMessResultOdd
iAdrsMessResultEven:      .int sMessResultEven
iAdrsZoneConv:            .int sZoneConv
/***************************************************/
/*     test if number is odd or even               */
/***************************************************/
// r0 contains à number
testOddEven:
    push {r2-r8,lr}             @ save  registers
    tst r0,#1                   @ test bit 0 to one
    beq 1f                      @ if result are all zéro, go to even
    ldr r1,iAdrsZoneConv        @ else display odd message
    bl conversion10             @ call decimal conversion
    ldr r0,iAdrsMessResultOdd
    ldr r1,iAdrsZoneConv        @ insert value conversion in message
    bl strInsertAtCharInc
    bl affichageMess
    b 100f
1:
    ldr r1,iAdrsZoneConv
    bl conversion10             @ call decimal conversion
    ldr r0,iAdrsMessResultEven
    ldr r1,iAdrsZoneConv        @ insert conversion in message
    bl strInsertAtCharInc
    bl affichageMess
100:
    pop {r2-r8,lr}             @ restaur registers
    bx lr                      @ return
/***************************************************/
/*      ROUTINES INCLUDE                           */
/***************************************************/
.include "../affichage.inc"

ArnoldC

LISTEN TO ME VERY CAREFULLY isOdd
I NEED YOUR CLOTHES YOUR BOOTS AND YOUR MOTORCYCLE n
GIVE THESE PEOPLE AIR
HEY CHRISTMAS TREE result
YOU SET US UP @I LIED
GET TO THE CHOPPER result
HERE IS MY INVITATION n
I LET HIM GO 2
ENOUGH TALK
I'LL BE BACK result
HASTA LA VISTA, BABY

LISTEN TO ME VERY CAREFULLY showParity
I NEED YOUR CLOTHES YOUR BOOTS AND YOUR MOTORCYCLE n
TALK TO THE HAND n
HEY CHRISTMAS TREE parity
YOU SET US UP @I LIED
GET YOUR A** TO MARS parity
DO IT NOW isOdd n
BECAUSE I'M GOING TO SAY PLEASE parity
TALK TO THE HAND "odd"
BULLS***
TALK TO THE HAND "even"
YOU HAVE NO RESPECT FOR LOGIC
TALK TO THE HAND ""
HASTA LA VISTA, BABY

IT'S SHOWTIME
DO IT NOW showParity 5
DO IT NOW showParity 6
DO IT NOW showParity -11
YOU HAVE BEEN TERMINATED

Output:

5
odd

6
even

-11
odd

Arturo

loop (neg 5)..5 [x][
	if? even? x -> print [pad to :string x 4 ": even"]
	else -> print [pad to :string x 4 ": odd"]
]

Output:

  -5 : odd 
  -4 : even 
  -3 : odd 
  -2 : even 
  -1 : odd 
   0 : even 
   1 : odd 
   2 : even 
   3 : odd 
   4 : even 
   5 : odd

Asymptote

for (int i = 1; i <= 10; ++i)  {
  if (i % 2 == 0) {
    write(string(i), " is even");
  } else {
    write(string(i), " is odd");
  }
}

AutoHotkey

Bitwise ops are probably most efficient:

if ( int & 1 ){
	; do odd stuff
}else{
	; do even stuff
}

AWK

function isodd(x) {
	return x % 2 != 0
}

function iseven(x) {
	return x % 2 == 0
}

BASIC

Applesoft BASIC

10 INPUT "ENTER A NUMBER: ";N
20 IF N/2 <> INT(N/2) THEN PRINT "THE NUMBER IS ODD":GOTO 40
30 PRINT "THE NUMBER IS EVEN"
40 END

Works with: Commodore BASIC version 2.0

BaCon

' Even or odd
OPTION MEMTYPE int
SPLIT ARGUMENT$ BY " " TO arg$ SIZE dim
n = IIF$(dim < 2, 0, VAL(arg$[1]))
PRINT n, " is ", IIF$(EVEN(n), "even", "odd")

Output:

prompt$ ./even-or-odd 42
42 is even
prompt$ ./even-or-odd 41
41 is odd

BASIC256

Works with: True BASIC

for i = 1 to 10
  if (i mod 2) then print i;" is odd" else print i;" is even"
next i
end

BBC BASIC

Works with: BBC BASIC for Windows

Solutions using AND or MOD are restricted to 32-bit integers, so an alternative solution is given which works with a larger range of values.

      IF FNisodd%(14) PRINT "14 is odd" ELSE PRINT "14 is even"
      IF FNisodd%(15) PRINT "15 is odd" ELSE PRINT "15 is even"
      IF FNisodd#(9876543210#) PRINT "9876543210 is odd" ELSE PRINT "9876543210 is even"
      IF FNisodd#(9876543211#) PRINT "9876543211 is odd" ELSE PRINT "9876543211 is even"
      END

      REM Works for -2^31 <= n% < 2^31
      DEF FNisodd%(n%) = (n% AND 1) <> 0

      REM Works for -2^53 <= n# <= 2^53
      DEF FNisodd#(n#) = n# <> 2 * INT(n# / 2)

Output:

14 is even
15 is odd
9876543210 is even
9876543211 is odd

Chipmunk Basic

Works with: Chipmunk Basic version 3.6.4

Uses bitwise AND as suggested.

10 cls
20 for n = 1 to 10
30  print n;
40  if (n and 1) = 1 then print "is odd" else print "is even"
50  next n
60 end

Commodore BASIC

Uses bitwise AND as suggested.

10 rem determine if integer is even or odd
20 print "Enter an integer:";
30 input i%
35 print
40 eo$="even"
50 if (i% and 1)=1 then eo$="odd"
60 print "The number ";i%;"is ";eo$;"."

FreeBASIC

' FB 1.05.0 Win64

Dim n As Integer

Do
  Print "Enter an integer or 0 to finish : ";
  Input "", n
  If n = 0 Then
    Exit Do
  ElseIf n Mod 2 = 0 Then
    Print "Your number is even"
    Print
  Else
    Print "Your number is odd"
    Print
  End if
Loop

End

Gambas

Public Sub Form_Open()
Dim sAnswer, sMessage As String

sAnswer = InputBox("Input an integer", "Odd or even")

If IsInteger(sAnswer) Then
  If Odd(Val(sAnswer)) Then sMessage = "' is an odd number"
  If Even(Val(sAnswer)) Then sMessage = "' is an even number"
Else
  sMessage = "' does not compute!!"
Endif

Print "'" & sAnswer & sMessage

End

Output:

'25' is an odd number
'100' is an even number
'Fred' does not compute!!

GW-BASIC

10 INPUT "Enter a number: ", N
20 IF N MOD 2 = 1 THEN PRINT "It is odd." ELSE PRINT "It is even."

IS-BASIC

100 DEF ODD(X)=MOD(X,2)
110 INPUT PROMPT "Enter a number: ":X
120 IF ODD(X) THEN
130   PRINT X;"is odd."
140 ELSE
150   PRINT X;"is even."
160 END IF

Liberty BASIC

Works with: Just BASIC

n=12

if n mod 2 = 0 then print "even" else print "odd"

Minimal BASIC

Works with: IS-BASIC

10 REM Even or odd
20 PRINT "Enter an integer number";
30 INPUT N
40 IF N/2 <> INT(N/2) THEN 70
50 PRINT "The number is even."
60 GOTO 80
70 PRINT "The number is odd."
80 END

MSX Basic

Uses bitwise AND as suggested.

10 CLS
20 FOR N = -5 TO 5
30 PRINT N;
40 IF (N AND 1) = 1 THEN PRINT "is odd" ELSE PRINT "is even"
50 NEXT N
60 END

PureBasic

;use last bit method
isOdd = i & 1         ;isOdd is non-zero if i is odd
isEven = i & 1 ! 1    ;isEven is non-zero if i is even

;use modular method
isOdd = i % 2         ;isOdd is non-zero if i is odd
isEven = i % 2 ! 1    ;isEven is non-zero if i is even

QB64

NB: Line numbers are not required in this language. Further, because of the Int variable type used for input, floating point values will not be accepted by the program. 0 is a problem, though, as it returns "Even" in the code below, even though it is not mathematically an even value. For code brevity, the 0 problem is not addressed. Finally, No Even or Odd predicates exist in this language.

'This is a comment line. It also could have been preceded with "Rem"

Dim i%          'This line is not necessary, but % strict casts
                'as an Int (2 bytes). "As Int" could have been used instead.
Input "#? ", i% 'Prints "#? " as a prompt and waits
                'for user input terminated by pressing [ENTER].

'Binary integers example
If i% And 1 Then 'Test whether the input value AND 1 is 0 (false) or 1 (true).
                 'There is no global or constant "True" or "False".
    Print "Odd"  'Prints "Odd" if the above tested "true".
Else             'This could have been also been "ElseIf Not (i% And 1)"
    Print "Even" 'Prints "Even in all other cases (Else)
                 'or if the logical inverse of the input value AND 1 tested
                 '"true" (ElseIf).
End If

'Modular congruence example
If i% Mod 2 Then
    Print "Still Odd"
Else
    Print "Still Even"
End If

QBasic

Works with: QBasic version 1.1

Works with: QuickBasic version 4.5

Works with: Run BASIC

FOR i = 1 TO 10
  IF i AND 1 THEN PRINT i; " is odd" ELSE PRINT i; " is even"
NEXT i

Quite BASIC

10 CLS
20 FOR n = -5 TO 5
30  PRINT n;
40  IF n % 2 <> 0 THEN PRINT " is odd" ELSE PRINT " is even"
50  NEXT n
60 END

Run BASIC

Works with: QBasic

for i = 1 to 10
  if i and 1 then print i;" is odd" else print i;" is even"
next i

1 is odd
2 is even
3 is odd
4 is even
5 is odd
6 is even
7 is odd
8 is even
9 is odd
10 is even

S-BASIC

S-BASIC lacks a MOD operator but supports bitwise operations on integer variables, so that is the approach taken.

rem - return true (-1) if even, otherwise false (0)
function even(i = integer) = integer
var one = integer    rem - both operands must be variables
one = 1
end = ((i and one) = 0)

rem - exercise the function
var i = integer
for i = 1 to 10 step 3
   print i; " is ";
   if even(i) then
     print "even"
   else
     print "odd"
next

end

Output:

 1 is odd
 4 is even
 7 is odd
 10 is even

TI-83 BASIC

TI-83 BASIC does not have a modulus operator.

If fPart(.5Ans
Then
Disp "ODD
Else
Disp "EVEN
End

Tiny BASIC

Works with: TinyBasic

10 PRINT "Enter a number:"
20 INPUT N
30 IF 2*(N/2) = N THEN GOTO 60
40 PRINT "It's odd."
50 END
60 PRINT "It's even."
70 END

True BASIC

Works with: BASIC256

FOR i = 1 to 10
    IF MOD(i, 2) = 0 THEN PRINT i; " is odd" ELSE PRINT i; " is even"
NEXT i
END

VBA

4 ways = 4 Functions :
IsEven ==> Use the even and odd predicates
IsEven2 ==> Check the least significant digit. With binary integers, i bitwise-and 1 equals 0 iff i is even
IsEven3 ==> Divide i by 2. The remainder equals 0 if i is even.
IsEven4 ==> Use modular congruences

Option Explicit

Sub Main_Even_Odd()
Dim i As Long

    For i = -50 To 48 Step 7
        Debug.Print i & " : IsEven ==> " & IIf(IsEven(i), "is even", "is odd") _
         & " " & Chr(124) & " IsEven2 ==> " & IIf(IsEven2(i), "is even", "is odd") _
         & " " & Chr(124) & " IsEven3 ==> " & IIf(IsEven3(i), "is even", "is odd") _
         & " " & Chr(124) & " IsEven4 ==> " & IIf(IsEven4(i), "is even", "is odd")
    Next
End Sub

Function IsEven(Number As Long) As Boolean
'Use the even and odd predicates
    IsEven = (WorksheetFunction.Even(Number) = Number)
End Function

Function IsEven2(Number As Long) As Boolean
'Check the least significant digit.
'With binary integers, i bitwise-and 1 equals 0 iff i is even, or equals 1 iff i is odd.
Dim lngTemp As Long
    lngTemp = CLng(Right(CStr(Number), 1))
    If (lngTemp And 1) = 0 Then IsEven2 = True
End Function

Function IsEven3(Number As Long) As Boolean
'Divide i by 2.
'The remainder equals 0 if i is even.
Dim sngTemp As Single
    sngTemp = Number / 2
    IsEven3 = ((Int(sngTemp) - sngTemp) = 0)
End Function

Function IsEven4(Number As Long) As Boolean
'Use modular congruences
    IsEven4 = (Number Mod 2 = 0)
End Function

Output:

-50 : IsEven ==> is even | IsEven2 ==> is even | IsEven3 ==> is even | IsEven4 ==> is even
-43 : IsEven ==> is odd | IsEven2 ==> is odd | IsEven3 ==> is odd | IsEven4 ==> is odd
-36 : IsEven ==> is even | IsEven2 ==> is even | IsEven3 ==> is even | IsEven4 ==> is even
-29 : IsEven ==> is odd | IsEven2 ==> is odd | IsEven3 ==> is odd | IsEven4 ==> is odd
-22 : IsEven ==> is even | IsEven2 ==> is even | IsEven3 ==> is even | IsEven4 ==> is even
-15 : IsEven ==> is odd | IsEven2 ==> is odd | IsEven3 ==> is odd | IsEven4 ==> is odd
-8 : IsEven ==> is even | IsEven2 ==> is even | IsEven3 ==> is even | IsEven4 ==> is even
-1 : IsEven ==> is odd | IsEven2 ==> is odd | IsEven3 ==> is odd | IsEven4 ==> is odd
6 : IsEven ==> is even | IsEven2 ==> is even | IsEven3 ==> is even | IsEven4 ==> is even
13 : IsEven ==> is odd | IsEven2 ==> is odd | IsEven3 ==> is odd | IsEven4 ==> is odd
20 : IsEven ==> is even | IsEven2 ==> is even | IsEven3 ==> is even | IsEven4 ==> is even
27 : IsEven ==> is odd | IsEven2 ==> is odd | IsEven3 ==> is odd | IsEven4 ==> is odd
34 : IsEven ==> is even | IsEven2 ==> is even | IsEven3 ==> is even | IsEven4 ==> is even
41 : IsEven ==> is odd | IsEven2 ==> is odd | IsEven3 ==> is odd | IsEven4 ==> is odd
48 : IsEven ==> is even | IsEven2 ==> is even | IsEven3 ==> is even | IsEven4 ==> is even

VBScript

Function odd_or_even(n)
	If n Mod 2 = 0 Then
		odd_or_even = "Even"
	Else
		odd_or_even = "Odd"
	End If
End Function

WScript.StdOut.Write "Please enter a number: "
n = WScript.StdIn.ReadLine
WScript.StdOut.Write n & " is " & odd_or_even(CInt(n))
WScript.StdOut.WriteLine

Output:

C:\>cscript /nologo odd_or_even.vbs
Please enter a number: 6
6 is Even

C:\>cscript /nologo odd_or_even.vbs
Please enter a number: 9
9 is Odd

C:\>cscript /nologo odd_or_even.vbs
Please enter a number: -1
-1 is Odd

Visual Basic .NET

Translation of: FreeBASIC

Module Module1

    Sub Main()
        Dim str As String
        Dim num As Integer
        While True
            Console.Write("Enter an integer or 0 to finish: ")
            str = Console.ReadLine()
            If Integer.TryParse(str, num) Then
                If num = 0 Then
                    Exit While
                End If
                If num Mod 2 = 0 Then
                    Console.WriteLine("Even")
                Else
                    Console.WriteLine("Odd")
                End If
            Else
                Console.WriteLine("Bad input.")
            End If
        End While
    End Sub

End Module

BigInteger

Library: System.Numerics

Imports System.Numerics

Module Module1
  Function IsOdd(bi As BigInteger) As Boolean
    Return Not bi.IsEven
  End Function

  Function IsEven(bi As BigInteger) As Boolean
    Return bi.IsEven
  End Function

  Sub Main()
    ' uncomment one of the following Dim statements
    ' Dim x As Byte = 3
    ' Dim x As Short = 3
    ' Dim x As Integer = 3
    ' Dim x As Long = 3
    ' Dim x As SByte = 3
    ' Dim x As UShort = 3
    ' Dim x As UInteger = 3
    ' Dim x As ULong = 3
    ' Dim x as BigInteger = 3
    ' the following three types give a warning, but will work
    ' Dim x As Single = 3
    ' Dim x As Double = 3
    ' Dim x As Decimal = 3

    Console.WriteLine("{0} {1}", IsOdd(x), IsEven(x))
  End Sub
End Module

XBasic

Works with: Windows XBasic

PROGRAM	"Even/Odd"

DECLARE FUNCTION  Entry ()

FUNCTION  Entry ()
  FOR i = 1 TO 10
    IF (i MOD 2) THEN PRINT i;" is odd" ELSE PRINT i;" is even"
  NEXT i
END FUNCTION

END PROGRAM

Yabasic

Translation of: Phix

for i = -5 to 5
    print i, and(i,1), mod(i,2)
next

ZX Spectrum Basic

10 FOR n=-3 TO 4: GO SUB 30: NEXT n
20 STOP
30 LET odd=FN m(n,2)
40 PRINT n;" is ";("Even" AND odd=0)+("Odd" AND odd=1)
50 RETURN
60 DEF FN m(a,b)=a-INT (a/b)*b

Batch File

@echo off
set /p i=Insert number:

::bitwise and
set /a "test1=%i%&1"

::divide last character by 2
set /a test2=%i:~-1%/2

::modulo
set /a test3=%i% %% 2

set test
pause>nul

bc

There are no bitwise operations, so this solution compares a remainder with zero. Calculation of i % 2 only works when scale = 0.

i = -3

/* Assumes that i is an integer. */
scale = 0
if (i % 2 == 0) "i is even
"
if (i % 2) "i is odd
"

Beads

beads 1 program 'Even or odd'

calc main_init
	loop across:[-10, -5, 10, 5] val:v
		log "{v}\todd:{is_odd(v)}\teven:{is_even(v)}"

Output:

-10	odd:N	even:Y
-5	odd:Y	even:N
10	odd:N	even:Y
5	odd:Y	even:N

Befunge

&2%52**"E"+,@

Outputs E if even, O if odd.

Binary Lambda Calculus

In lambda calculus, the oddness of a given church numeral n can be computed as n applications of not to false: \n. n (\b\x\y. b y x) (\x\y.y), which in BLC is

00 01 01 10 0000000101111010110 000010

To compute the evenness, one need only replace false by true, i.e. replace the final 0 bit by 10.

BQN

odd ← 2⊸|

!0 ≡ odd 12
!1 ≡ odd 31

Bracmat

Not the simplest solution, but the cheapest if the number that must be tested has thousands of digits.

( ( even
  =
    . @( !arg
       :   ?
           [-2
           ( 0
           | 2
           | 4
           | 6
           | 8
           )
       )
  )
& (odd=.~(even$!arg))
& ( eventest
  =
    .   out
      $ (!arg is (even$!arg&|not) even)
  )
& ( oddtest
  =
    .   out
      $ (!arg is (odd$!arg&|not) odd)
  )
& eventest$5556
& oddtest$5556
& eventest$857234098750432987502398457089435
& oddtest$857234098750432987502398457089435
)

Output:

5556 is even
5556 is not odd
857234098750432987502398457089435 is not even
857234098750432987502398457089435 is odd

Brainf***

Assumes that input characters are an ASCII representation of a valid integer. Output is input mod 2.

,[>,----------] Read until newline
++<             Get a 2 and move into position
[->-[>+>>]>     Do
[+[-<+>]>+>>]   divmod
<<<<<]          magic
>[-]<++++++++   Clear and get an 8
[>++++++<-]     to get a 48
>[>+<-]>.       to get n % 2 to ASCII and print

If one need only determine rather than act on the parity of the input, the following is sufficient; it terminates either quickly or never.

,[>,----------]<[--]

Burlesque

2.%

C

Test by bitwise and'ing 1, works for any builtin integer type as long as it's 2's complement (it's always so nowadays):

if (x & 1) {
    /* x is odd */
} else {
    /* or not */
}

If using long integer type from GMP (mpz_t), there are provided macros:

mpz_t x;
...
if (mpz_even_p(x)) { /* x is even */ }
if (mpz_odd_p(x))  { /* x is odd */ }

The macros evaluate x more than once, so it should not be something with side effects.

C#

namespace RosettaCode
{
    using System;

    public static class EvenOrOdd
    {
        public static bool IsEvenBitwise(this int number)
        {
            return (number & 1) == 0;
        }

        public static bool IsOddBitwise(this int number)
        {
            return (number & 1) != 0;
        }

        public static bool IsEvenRemainder(this int number)
        {
            int remainder;
            Math.DivRem(number, 2, out remainder);
            return remainder == 0;
        }

        public static bool IsOddRemainder(this int number)
        {
            int remainder;
            Math.DivRem(number, 2, out remainder);
            return remainder != 0;
        }

        public static bool IsEvenModulo(this int number)
        {
            return (number % 2) == 0;
        }

        public static bool IsOddModulo(this int number)
        {
            return (number % 2) != 0;
        }
    }
    public class Program
    {
        public static void Main()
        {
            int num = 26;               //Set this to any integer.
            if (num.IsEvenBitwise())    //Replace this with any even function.
            {
                Console.Write("Even");
            }
            else
            {
                Console.Write("Odd");
            }
            //Prints "Even".
            if (num.IsOddBitwise())    //Replace this with any odd function.
            {
                Console.Write("Odd");
            }
            else
            {
                Console.Write("Even");
            }
            //Prints "Even".
        }
    }
}

C++

Test using the modulo operator, or use the C example from above.

bool isOdd(int x)
{
    return x % 2;
}

bool isEven(int x)
{
    return !(x % 2);
}

A slightly more type-generic version, for C++11 and later. This should theoretically work for any type convertible to int:

template < typename T >
constexpr inline bool isEven( const T& v )
{
    return isEven( int( v ) );
}

template <>
constexpr inline bool isEven< int >( const int& v )
{
    return (v & 1) == 0;
}

template < typename T >
constexpr inline bool isOdd( const T& v )
{
    return !isEven(v);
}

Clojure

Standard predicates:

(if (even? some-var) (do-even-stuff))
(if (odd? some-var) (do-odd-stuff))

COBOL

       IF FUNCTION REM(Num, 2) = 0
           DISPLAY Num " is even."
       ELSE
           DISPLAY Num " is odd."
       END-IF

CoffeeScript

isEven = (x) -> !(x%2)

ColdFusion

function f(numeric n) {
   return n mod 2?"odd":"even"
}

Common Lisp

Standard predicates:

(if (evenp some-var) (do-even-stuff))
(if (oddp some-other-var) (do-odd-stuff))

Alternate solution

I use Allegro CL 10.1

;; Project : Even or odd

(defun evenodd (nr)
          (cond ((evenp nr) "even")
          ((oddp nr) "odd")))
(dotimes (n 10)
(if (< n 1) (terpri))
(if (< n 9) (format t "~a" " "))
(write(+ n 1)) (format t "~a" ": ")
(format t "~a" (evenodd (+ n 1))) (terpri))

Output:

1: odd
 2: even
 3: odd
 4: even
 5: odd
 6: even
 7: odd
 8: even
 9: odd
10: even

Component Pascal

BlackBox Component Builder

MODULE EvenOdd;
IMPORT StdLog,Args,Strings;

PROCEDURE BitwiseOdd(i: INTEGER): BOOLEAN;
BEGIN
	RETURN 0 IN BITS(i)
END BitwiseOdd;

PROCEDURE Odd(i: INTEGER): BOOLEAN;
BEGIN
	RETURN (i MOD 2) # 0
END Odd;

PROCEDURE CongruenceOdd(i: INTEGER): BOOLEAN;
BEGIN
	RETURN ((i -1) MOD 2) = 0
END CongruenceOdd;

PROCEDURE Do*;
VAR
	p: Args.Params;
	i,done,x: INTEGER;
BEGIN
	Args.Get(p);
	StdLog.String("Builtin function: ");StdLog.Ln;i := 0;
	WHILE i < p.argc DO
		Strings.StringToInt(p.args[i],x,done);
		StdLog.String(p.args[i] + " is:> ");
		IF ODD(x) THEN StdLog.String("odd") ELSE StdLog.String("even") END;
		StdLog.Ln;INC(i)
	END;
	StdLog.String("Bitwise: ");StdLog.Ln;i:= 0;
	WHILE i < p.argc DO
		Strings.StringToInt(p.args[i],x,done);
		StdLog.String(p.args[i] + " is:> ");
		IF BitwiseOdd(x) THEN StdLog.String("odd") ELSE StdLog.String("even") END;
		StdLog.Ln;INC(i)
	END;
	StdLog.String("Module: ");StdLog.Ln;i := 0;
	WHILE i < p.argc DO
		Strings.StringToInt(p.args[i],x,done);
		StdLog.String(p.args[i] + " is:> ");
		IF Odd(x) THEN StdLog.String("odd") ELSE StdLog.String("even") END;
		StdLog.Ln;INC(i)
	END;
	StdLog.String("Congruences: ");StdLog.Ln;i := 0;
	WHILE i < p.argc DO
		Strings.StringToInt(p.args[i],x,done);
		StdLog.String(p.args[i] + " is:> ");
		IF CongruenceOdd(x) THEN StdLog.String("odd") ELSE StdLog.String("even") END;
		StdLog.Ln;INC(i)
	END;
END Do;

Execute: ^Q EvenOdd.Do 10 11 0 57 34 -23 -42~

Output:

Builtin function: 
10  is:> even
11  is:> odd
0  is:> even
57  is:> odd
34  is:> even
-23  is:> odd
-42 is:> even
Bitwise: 
10  is:> even
11  is:> odd
0  is:> even
57  is:> odd
34  is:> even
-23  is:> odd
-42 is:> even
Module: 
10  is:> even
11  is:> odd
0  is:> even
57  is:> odd
34  is:> even
-23  is:> odd
-42 is:> even
Congruences: 
10  is:> even
11  is:> odd
0  is:> even
57  is:> odd
34  is:> even
-23  is:> odd
-42 is:> even

Crystal

#Using bitwise shift
  def isEven_bShift(n)
    n == ((n >> 1) << 1)
  end
  def isOdd_bShift(n)
    n != ((n >> 1) << 1)
  end
#Using modulo operator
  def isEven_mod(n)
    (n % 2) == 0
  end
  def isOdd_mod(n)
    (n % 2) != 0
  end
# Using bitwise "and"
  def isEven_bAnd(n)
    (n & 1) ==  0
  end
  def isOdd_bAnd(n)
    (n & 1) != 0
  end

puts isEven_bShift(7)
puts isOdd_bShift(7)

puts isEven_mod(12)
puts isOdd_mod(12)

puts isEven_bAnd(21)
puts isOdd_bAnd(21)

Output:

false
true
true
false
false
true

D

void main() {
    import std.stdio, std.bigint;

    foreach (immutable i; -5 .. 6)
        writeln(i, " ", i & 1, " ", i % 2, " ", i.BigInt % 2);
}

Output:

-5 1 -1 -1
-4 0 0 0
-3 1 -1 -1
-2 0 0 0
-1 1 -1 -1
0 0 0 0
1 1 1 1
2 0 0 0
3 1 1 1
4 0 0 0
5 1 1 1

Dart

void main() {
  for (var i = 1; i <= 10; i++) {
    if (i % 2 != 0) {
      print("$i is odd");
    } else {
      print("$i is even");
    }
  }
}

dc

This macro expects an integer on the stack, pops it, and pushes 1 if it is odd, or 0 if it is even (independently from the precision currently set).

[K Sk 0 k 2 % Lk k]

DCL

$! in DCL, for integers, the least significant bit determines the logical value, where 1 is true and 0 is false
$
$ i = -5
$ loop1:
$  if i then $ write sys$output i, " is odd"
$  if .not. i then $ write sys$output i, " is even"
$  i = i + 1
$  if i .le. 6 then $ goto loop1

Output:

$ @even_odd
-5 is odd
-4 is even
-3 is odd
-2 is even
-1 is odd
0 is even
1 is odd
2 is even
3 is odd
4 is even
5 is odd
6 is even

Delphi

program EvenOdd;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;

procedure IsOdd(aValue: Integer);
var
  Odd: Boolean;
begin
  Odd :=  aValue and 1 <> 0;
  Write(Format('%d is ', [aValue]));
  if Odd then
    Writeln('odd')
  else
    Writeln('even');
end;

var
  i: Integer;
begin
  for i := -5 to 10 do
    IsOdd(i);

  Readln;
end.

Output:

-5 is odd
-4 is even
-3 is odd
-2 is even
-1 is odd
0 is even
1 is odd
2 is even
3 is odd
4 is even
5 is odd
6 is even
7 is odd
8 is even
9 is odd
10 is even

Déjà Vu

even n:
    = 0 % n 2

odd:
    not even

!. odd 0
!. even 0
!. odd 7
!. even 7

Output:

false
true
true
false

Diego

use_namespace(rosettacode)_me();

funct(isEven)_arg(i)_ret()_calc(i%2)_equals(0);

reset_namespace[];

DWScript

Predicate:

var isOdd := Odd(i);

Bitwise and:

var isOdd := (i and 1)<>0;

Modulo:

var isOdd := (i mod 2)=1;

EasyLang

a = 13
if a mod 2 = 0
   print a & " is even"
else
   print a & " is odd"
.

EDSAC order code

This implementation uses the C (logical AND multiplier register with memory) order. It will cause the machine to print an E if the number stored at address θ+15 is even, or an O if it is odd. As an example, we shall test the number 37 (P18D in EDSAC encoding).

[ Even or odd
  ===========

  A program for the EDSAC

  Determines whether the number stored at
  address 15@ is even or odd, and prints
  'E' or 'O' accordingly

  Works with Initial Orders 2 ]

       T56K   [ load point ]
       GK     [ base address ]

       O11@   [ print letter shift ]
       T10@   [ clear accumulator ]
       H15@   [ multiplier := n ]
       C12@   [ acc +:= mult AND 1 ]
       S12@   [ acc -:= 1 ]
       G8@    [ branch on negative ]
       O14@   [ print 'O' ]
       ZF     [ halt ]
[ 8 ]  O13@   [ print 'E' ]
       ZF     [ halt ]

[ 10 ] P0F    [ used to clear acc ]
[ 11 ] *F     [ letter shift character ]
[ 12 ] P0D    [ const: 1 ]
[ 13 ] EF     [ character 'E' ]
[ 14 ] OF     [ character 'O' ]
[ 15 ] P18D   [ number to test: 37 ]

       EZPF   [ branch to load point ]

Output:

O

Eiffel

--bit testing
if i.bit_and (1) = 0 then
	-- i is even
end

--built-in bit testing (uses bit_and)
if i.bit_test (0) then
	-- i is odd
end

--integer remainder (modulo)
if i \\ 2 = 0 then
	-- i is even
end

Elixir

defmodule RC do
  import Integer

  def even_or_odd(n) when is_even(n), do: "#{n} is even"
  def even_or_odd(n)                , do: "#{n} is odd"
      # In second "def", the guard clauses of "is_odd(n)" is unnecessary.

  # Another definition way
  def even_or_odd2(n) do
    if is_even(n), do: "#{n} is even", else: "#{n} is odd"
  end
end

Enum.each(-2..3, fn n -> IO.puts RC.even_or_odd(n) end)

Output:

-2 is even
-1 is odd
0 is even
1 is odd
2 is even
3 is odd

Other ways to test even-ness:

rem(n,2) == 0

Emacs Lisp

(require 'cl-lib)

(defun even-or-odd-p (n)
  (if (cl-evenp n) 'even 'odd))

(defun even-or-odd-p (n)
 (if (zerop (% n 2)) 'even 'odd))

(message "%d is %s" 3 (even-or-oddp 3))
(message "%d is %s" 2 (even-or-oddp 2))

Output:

3 is odd
2 is even

EMal

List evenCheckers = fun[
  logic by int i do return i % 2 == 0 end,
  logic by int i do return i & 1 == 0 end]
List oddCheckers = fun[
  logic by int i do return i % 2 != 0 end,
  logic by int i do return i & 1 == 1 end]
writeLine("integer".padStart(10, " ") + "|is_even" + "|is_odd |")  
writeLine("----------+-------+-------+")
for each int i in range(-5, 6).append(3141592653)
  write((text!i).padStart(10, " ") + "| ")
  for each fun isEven in evenCheckers
    write(isEven(i) + "  ")
  end
  write("| ")
  for each fun isOdd in oddCheckers
    write(isOdd(i) + "  ")
  end
  writeLine("|")
end
writeLine("----------+-------+-------+")

Output:

   integer|is_even|is_odd |
----------+-------+-------+
        -5| ⊥  ⊥  | ⊤  ⊤  |
        -4| ⊤  ⊤  | ⊥  ⊥  |
        -3| ⊥  ⊥  | ⊤  ⊤  |
        -2| ⊤  ⊤  | ⊥  ⊥  |
        -1| ⊥  ⊥  | ⊤  ⊤  |
         0| ⊤  ⊤  | ⊥  ⊥  |
         1| ⊥  ⊥  | ⊤  ⊤  |
         2| ⊤  ⊤  | ⊥  ⊥  |
         3| ⊥  ⊥  | ⊤  ⊤  |
         4| ⊤  ⊤  | ⊥  ⊥  |
         5| ⊥  ⊥  | ⊤  ⊤  |
3141592653| ⊥  ⊥  | ⊤  ⊤  |
----------+-------+-------+

Erlang

Using Division by 2 Method

%% Implemented by Arjun Sunel
-module(even_odd).
-export([main/0]).

main()->
	test(8).

test(N) ->
	if (N rem 2)==1 ->
		io:format("odd\n");
	true ->
		io:format("even\n")
	end.

Using the least-significant bit method

 %% Implemented by Arjun Sunel
-module(even_odd2).
-export([main/0]).

main()->
	test(10).

test(N) ->
	if (N band 1)==1 ->
		io:format("odd\n");
	true ->
		io:format("even\n")
	end.

ERRE

PROGRAM ODD_EVEN

! works for -2^15 <= n% < 2^15

FUNCTION ISODD%(N%)
      ISODD%=(N% AND 1)<>0
END FUNCTION

! works for -2^38 <= n# <= 2^38
FUNCTION ISODD#(N#)
      ISODD#=N#<>2*INT(N#/2)
END FUNCTION

BEGIN
  IF ISODD%(14) THEN PRINT("14 is odd") ELSE PRINT("14 is even") END IF
  IF ISODD%(15) THEN PRINT("15 is odd") ELSE PRINT("15 is even") END IF
  IF ISODD#(9876543210) THEN PRINT("9876543210 is odd") ELSE PRINT("9876543210 is even") END IF
  IF ISODD#(9876543211) THEN PRINT("9876543211 is odd") ELSE PRINT("9876543211 is even") END IF
END PROGRAM

Output:

14 is even
15 is odd
9876543210 is even
9876543211 is odd

Euphoria

Using standard function

include std/math.e

for i = 1 to 10 do
        ? {i, is_even(i)}
end for

Output:

{1,0}
{2,1}
{3,0}
{4,1}
{5,0}
{6,1}
{7,0}
{8,1}
{9,0}
{10,1}

Excel

Use the MOD function

=MOD(33;2)
=MOD(18;2)

Output:

1
0

Use the ISEVEN function, returns TRUE or FALSE

=ISEVEN(33)
=ISEVEN(18)

Output:

FALSE
TRUE

Use the ISODD function, returns TRUE or FALSE

=ISODD(33)
=ISODD(18)

Output:

TRUE
FALSE

F#

Bitwise and:

let isEven x =
  x &&& 1 = 0

Modulo:

let isEven x =
  x % 2 = 0

Factor

The math vocabulary provides even? and odd? predicates. This example runs at the listener, which already uses the math vocabulary.

( scratchpad ) 20 even? .
t
( scratchpad ) 35 even? .
f
( scratchpad ) 20 odd? .
f
( scratchpad ) 35 odd? .
t

Fish

This example assumes that the input command i returns an integer when one was inputted and that the user inputs a valid positive integer terminated by a newline.

<v"Please enter a number:"a
 >l0)?!vo     v          <                        v    o<
^      >i:a=?v>i:a=?v$a*+^>"The number is even."ar>l0=?!^>
             >      >2%0=?^"The number is odd."ar ^

The actual computation is the 2%0= part. The rest is either user interface or parsing input.

Forth

: odd?  ( n -- ? ) 1 and ;
: even? ( n -- ? ) odd? 0= ;

\ Every value not equal to zero is considered true. Only zero is considered false.

Fortran

Please find the compilation and example run in the comments at the beginning of the FORTRAN 2008 source. Separating the bit 0 parity module from the main program enables reuse of the even and odd functions. Even and odd, with scalar and vector interfaces demonstrate the generic function capability of FORTRAN 90. Threading, stdin, and all-intrinsics are vestigial and have no influence here other than to confuse you.

!-*- mode: compilation; default-directory: "/tmp/" -*-
!Compilation started at Tue May 21 20:22:56
!
!a=./f && make $a && OMP_NUM_THREADS=2 $a < unixdict.txt
!gfortran -std=f2008 -Wall -ffree-form -fall-intrinsics f.f08 -o f
! n     odd    even
!-6    F    T
!-5    T    F
!-4    F    T
!-3    T    F
!-2    F    T
!-1    T    F
! 0    F    T
! 1    T    F
! 2    F    T
! 3    T    F
! 4    F    T
! 5    T    F
! 6    F    T
! -6 -5 -4 -3 -2 -1  0  1  2  3  4  5  6       n
!  F  T  F  T  F  T  F  T  F  T  F  T  F     odd
!  T  F  T  F  T  F  T  F  T  F  T  F  T    even
!
!Compilation finished at Tue May 21 20:22:56


module bit0parity

  interface odd
    module procedure odd_scalar, odd_list
  end interface

  interface even
    module procedure even_scalar, even_list
  end interface

contains

  logical function odd_scalar(a)
    implicit none
    integer, intent(in) :: a
    odd_scalar = btest(a, 0)
  end function odd_scalar

  logical function even_scalar(a)
    implicit none
    integer, intent(in) :: a
    even_scalar = .not. odd_scalar(a)
  end function even_scalar

  function odd_list(a) result(rv)
    implicit none
    integer, dimension(:), intent(in) :: a
    logical, dimension(size(a)) :: rv
    rv = btest(a, 0)
  end function odd_list

  function even_list(a) result(rv)
    implicit none
    integer, dimension(:), intent(in) :: a
    logical, dimension(size(a)) :: rv
    rv = .not. odd_list(a)
  end function even_list

end module bit0parity

program oe
  use bit0parity
  implicit none
  integer :: i
  integer, dimension(13) :: j
  write(6,'(a2,2a8)') 'n', 'odd', 'even'
  write(6, '(i2,2l5)') (i, odd_scalar(i), even_scalar(i), i=-6,6)
  do i=-6, 6
    j(i+7) = i
  end do
  write(6, '((13i3),a8/(13l3),a8/(13l3),a8)') j, 'n', odd(j), 'odd', even(j), 'even'
end program oe

Frink

isEven[x is isInteger] := getBit[x,0] == 0
isOdd[x is isInteger] := getBit[x,0] == 1

Futhark

This example is incorrect. Please fix the code and remove this message. Details: Futhark's syntax has changed, so this example will not compile

fun main(x: int): bool = (x & 1) == 0

FutureBasic

local fn OddOrEven( i as NSInteger ) as CFStringRef
  CFStringRef result
  if ( i mod 2 ) == 0 then result = @"Even" else result = @"Odd"
end fn = result

NSUInteger i

for i = 1 to 10
  printf @"%d is %@", i, fn OddOrEven( i )
next

HandleEvents

Fōrmulæ

Fōrmulæ programs are not textual, visualization/edition of programs is done showing/manipulating structures but not text. Moreover, there can be multiple visual representations of the same program. Even though it is possible to have textual representation —i.e. XML, JSON— they are intended for storage and transfer purposes more than visualization and edition.

Programs in Fōrmulæ are created/edited online in its website.

In this page you can see and run the program(s) related to this task and their results. You can also change either the programs or the parameters they are called with, for experimentation, but remember that these programs were created with the main purpose of showing a clear solution of the task, and they generally lack any kind of validation.

Solutions

Case 1. Intrinsic expressions:

Case 2. Using the Divides and DoesNotDivide expressions:

Case 3. Using modular congruences

Case 4. Using bitwise operations

Case 5. Using IsRational

GAP

IsEvenInt(n);
IsOddInt(n);

Genie

Using bitwise AND of the zero-bit.

[indent = 4]
/*
   Even or odd, in Genie
   valac even_or_odd.gs
*/

def parity(n:int):bool
    return ((n & 1) == 0)

def show_parity(n:int):void
    print "%d is %s", n, parity(n) ? "even" : "odd"

init
    show_parity(0)
    show_parity(1)
    show_parity(2)
    show_parity(-2)
    show_parity(-1)

Output:

prompt$ valac even_or_odd.gs
prompt$ ./even_or_odd
0 is even
1 is odd
2 is even
-2 is even
-1 is odd

Go

package main

import (
    "fmt"
    "math/big"
)

func main() {
    test(-2)
    test(-1)
    test(0)
    test(1)
    test(2)
    testBig("-222222222222222222222222222222222222")
    testBig("-1")
    testBig("0")
    testBig("1")
    testBig("222222222222222222222222222222222222")
}

func test(n int) {
    fmt.Printf("Testing integer %3d:  ", n)
    // & 1 is a good way to test
    if n&1 == 0 {
        fmt.Print("even ")
    } else {
        fmt.Print(" odd ")
    }
    // Careful when using %: negative n % 2 returns -1.  So, the code below
    // works, but can be broken by someone thinking they can reverse the
    // test by testing n % 2 == 1.  The valid reverse test is n % 2 != 0.
    if n%2 == 0 {
        fmt.Println("even")
    } else {
        fmt.Println(" odd")
    }
}

func testBig(s string) {
    b, _ := new(big.Int).SetString(s, 10)
    fmt.Printf("Testing big integer %v:  ", b)
    // the Bit function is the only sensible test for big ints.
    if b.Bit(0) == 0 {
        fmt.Println("even")
    } else {
        fmt.Println("odd")
    }
}

Output:

Testing integer  -2:  even even
Testing integer  -1:   odd  odd
Testing integer   0:  even even
Testing integer   1:   odd  odd
Testing integer   2:  even even
Testing big integer -222222222222222222222222222222222222:  even
Testing big integer -1:  odd
Testing big integer 0:  even
Testing big integer 1:  odd
Testing big integer 222222222222222222222222222222222222:  even

Groovy

Solution:

def isOdd = { int i -> (i & 1) as boolean }
def isEven = {int i -> ! isOdd(i) }

Test:

1.step(20, 2) { assert isOdd(it) }

50.step(-50, -2) { assert isEven(it) }

Haskell

even and odd functions are already included in the standard Prelude.

Prelude> even 5
False
Prelude> even 42
True
Prelude> odd 5
True
Prelude> odd 42
False

Where even is derived from rem, and odd is derived from even:

import Prelude hiding (even, odd)

even, odd
  :: (Integral a)
  => a -> Bool
even = (0 ==) . (`rem` 2)

odd = not . even

main :: IO ()
main = print (even <$> [0 .. 9])

Output:

[True,False,True,False,True,False,True,False,True,False]

Hoon

|=  n=@ud
?:  =((mod n 2) 0)
  "even"
"odd"

Icon and Unicon

One way is to check the remainder:

procedure isEven(n)
    return n%2 = 0
end

Insitux

Exactly the same as Clojure, these are built-in predicates.

(if (even? some-var) (do-even-stuff))
(if (odd? some-var) (do-odd-stuff))

J

Modulo:

   2 | 2 3 5 7
0 1 1 1
   2|2 3 5 7 + (2^89x)-1
1 0 0 0

Remainder:

   (= <.&.-:) 2 3 5 7
1 0 0 0
   (= <.&.-:) 2 3 5 7+(2^89x)-1
0 1 1 1

Last bit in bit representation:

   {:"1@#: 2 3 5 7
0 1 1 1
   {:"1@#: 2 3 5 7+(2^89x)-1
1 0 0 0

Bitwise and:

   1 (17 b.) 2 3 5 7
0 1 1 1

Note: as a general rule, the simplest expressions in J should be preferred over more complex approaches.

Jakt

fn is_even<T>(anon n: T) -> bool => 0 == (n & 1)

fn is_odd<T>(anon n: T) -> bool => 0 != (n & 1)

fn main() {
    for i in 0..11 {
        println("{} {} {}", i, is_even(i), is_odd(i))
    }
}

Java

Bitwise and:

public static boolean isEven(int i){
    return (i & 1) == 0;
}

Modulo:

public static boolean isEven(int i){
    return (i % 2) == 0;
}

Arbitrary precision bitwise:

public static boolean isEven(BigInteger i){
    return i.and(BigInteger.ONE).equals(BigInteger.ZERO);
}

Arbitrary precision bit test (even works for negative numbers because of the way BigInteger represents the bits of numbers):

public static boolean isEven(BigInteger i){
    return !i.testBit(0);
}

Arbitrary precision modulo:

public static boolean isEven(BigInteger i){
    return i.mod(BigInteger.valueOf(2)).equals(BigInteger.ZERO);
}

JavaScript

ES5

Bitwise:

function isEven( i ) {
  return (i & 1) === 0;
}

Modulo:

function isEven( i ) {
  return i % 2 === 0;
}

// Alternative
function isEven( i ) {
  return !(i % 2);
}

ES6

Lambda:

// EMCAScript 6
const isEven = x => !(x % 2)

or, avoiding type coercion:

(() => {
    'use strict';

    // even : Integral a => a -> Bool
    const even = x => (x % 2) === 0;

    // odd : Integral a => a -> Bool
    const odd = x => !even(x);


    // TEST ----------------------------------------
    // range :: Int -> Int -> [Int]
    const range = (m, n) =>
        Array.from({
            length: Math.floor(n - m) + 1
        }, (_, i) => m + i);

    // show :: a -> String
    const show = JSON.stringify;

    // xs :: [Int]
    const xs = range(-6, 6);

    return show([xs.filter(even), xs.filter(odd)]);
})();

Output:

[[-6,-4,-2,0,2,4,6],[-5,-3,-1,1,3,5]]

Joy

DEFINE
  even == 2 rem null;
  odd == even not.

jq

In practice, to test whether an integer, i, is even or odd in jq, one would typically use: i % 2

For example, if it were necessary to have a strictly boolean function that would test if its input is an even integer, one could define:

def is_even: type == "number" and floor == 0 and . % 2 == 0;

The check that the floor is 0 is necessary as % is defined on floating point numbers.

"is_odd" could be similarly defined:

def is_odd: type == "number" and floor == 0 and . % 2 == 1;

Jsish

Using bitwise and of low bit.

#!/usr/bin/env jsish
/* Even or Odd, in Jsish */
function isEven(n:number):boolean { return (n & 1) === 0; }

provide('isEven', 1);

if (Interp.conf('unitTest')) {
;    isEven(0);
;    isEven(1);
;    isEven(2);
;    isEven(-13);
}

/*
=!EXPECTSTART!=
isEven(0) ==> true
isEven(1) ==> false
isEven(2) ==> true
isEven(-13) ==> false
=!EXPECTEND!=
*/

Output:

$ jsish --U isEven.jsi
isEven(0) ==> true
isEven(1) ==> false
isEven(2) ==> true
isEven(-13) ==> false

Julia

Built-in functions:

iseven(i), isodd(i)

K

The following implementation uses the modulo of division by 2

oddp: {:[x!2;1;0]} /Returns 1 if arg. is odd
evenp: {~oddp[x]}  /Returns 1 if arg. is even

Examples:
   oddp 32
0
   evenp 32
1

Klingphix

( -5 5 ) [
    dup print " " print 2 mod ( ["Odd"] ["Even"] ) if print nl
] for

" " input

Output:

-5 Odd
-4 Even
-3 Odd
-2 Even
-1 Odd
0 Even
1 Odd
2 Even
3 Odd
4 Even
5 Odd

Kotlin

// version 1.0.5-2

fun main(args: Array<String>) {
    while (true) {
        print("Enter an integer or 0 to finish : ")
        val n = readLine()!!.toInt()
        when {
            n == 0     -> return
            n % 2 == 0 -> println("Your number is even")
            else       -> println("Your number is odd")
        }
    }
}

Lambdatalk

{def is_odd {lambda {:i} {= {% :i 2} 1}}}
-> is_odd

{def is_even {lambda {:i} {= {% :i 2} 0}}}
-> is_even

{is_odd 2}
-> false

{is_even 2}
-> true

L++

(defn bool isEven (int x) (return (% x 2)))

LabVIEW

Using bitwise And
This image is a VI Snippet, an executable image of LabVIEW code. The LabVIEW version is shown on the top-right hand corner. You can download it, then drag-and-drop it onto the LabVIEW block diagram from a file browser, and it will appear as runnable, editable code.

Lang5

: even?  2 % not ;
: odd?  2 % ;
1 even? .   # 0
1 odd? .    # 1

Lasso

define isoddoreven(i::integer) => {
	#i % 2 ? return 'odd'
	return 'even'
}
isoddoreven(12)

LC3 Assembly

Prints EVEN if the number stored in NUM is even, otherwise ODD.

      .ORIG      0x3000

      LD         R0,NUM
      AND        R1,R0,1
      BRZ        EVEN

      LEA        R0,ODD
      BRNZP      DISP

EVEN  LEA        R0,EVN

DISP  PUTS

      HALT

NUM   .FILL      0x1C

EVN   .STRINGZ   "EVEN\n"
ODD   .STRINGZ   "ODD\n"

      .END

Lingo

on even (n)
  return n mod 2 = 0
end

on odd (n)
  return n mode 2 <> 0
end

Little Man Computer

Runs in Peter Higginson's simulator, to allow comments. Does not use his other extensions to the language.

LMC has no division instruction. To divide by 2 we could use repeated subtraction:

// Input number; output its residue mod 2
       INP        // read input into acc
       BRZ write  // input = 0 is special case
loop   SUB k2     // keep subtracting 2 from acc
       BRZ write  // if acc = 0, input is even
       BRP loop   // if acc > 0, loop back
                  // (BRP branches if acc >= 0, but we've dealt with acc = 0)
       LDA k1     // if acc < 0, input is odd
write  OUT        // output 0 or 1
       HLT        // halt
k1     DAT 1      // constant 1
k2     DAT 2      // constant 2
// end

The above program might need 500 subtractions before it found the result. To speed things up we could use something along the following lines.

// Input number; output its residue mod 2
         INP          // read input into accumulator
loop1    STA save_acc // save accumulator (see note below)
         SUB k128     // keep subtracting 128 until acc < 0
         BRP loop1
         LDA save_acc // save_acc holds a number in range 0..127
loop2    STA save_acc
         SUB k16      // keep subtracting 16 until acc < 0
         BRP loop2
         LDA save_acc // save_acc holds a number in range 0..15
loop3    STA save_acc
         SUB k2       // keep subtracting 2 until acc < 0
         BRP loop3
         LDA save_acc // save_acc holds 0 or 1, the result
write    OUT          // output result
         HLT
k2       DAT 2
k16      DAT 16
k128     DAT 128
save_acc DAT
// end

Note: LMC, in its original form, does not support negative numbers. If the accumulator contains a number X, and a number Y > X is subtracted, then the negative flag is set and the value in the accumulator becomes undefined. So we can't assume that adding Y back to the accumulator will restore the value of X. If we want to use X again, we need to save it in RAM before doing the subtraction.

LiveCode

function odd n
    return (n bitand 1) = 1
end odd

function notEven n
    return (n mod 2) = 1
end notEven

LLVM

; This is not strictly LLVM, as it uses the C library function "printf".
; LLVM does not provide a way to print values, so the alternative would be
; to just load the string into memory, and that would be boring.

; Additional comments have been inserted, as well as changes made from the output produced by clang such as putting more meaningful labels for the jumps

;--- The declarations for the external C functions
declare i32 @printf(i8*, ...)

$"EVEN_STR" = comdat any
$"ODD_STR" = comdat any

@"EVEN_STR" = linkonce_odr unnamed_addr constant [12 x i8] c"%d is even\0A\00", comdat, align 1
@"ODD_STR" = linkonce_odr unnamed_addr constant [11 x i8] c"%d is odd\0A\00", comdat, align 1

; Function Attrs: noinline nounwind optnone uwtable
define i32 @main() #0 {
  %1 = alloca i32, align 4          ;-- allocate i
  store i32 0, i32* %1, align 4     ;-- store 0 in i
  br label %loop

loop:
  %2 = load i32, i32* %1, align 4   ;-- load i
  %3 = icmp ult i32 %2, 4           ;-- i < 4
  br i1 %3, label %loop_body, label %exit

loop_body:
  %4 = load i32, i32* %1, align 4   ;-- load i
  %5 = and i32 %4, 1                ;-- i & 1
  %6 = icmp eq i32 %5, 0            ;-- (i & 1) == 0
  br i1 %6, label %even_branch, label %odd_branch

even_branch:
  %7 = load i32, i32* %1, align 4   ;-- load i
  %8 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([12 x i8], [12 x i8]* @"EVEN_STR", i32 0, i32 0), i32 %7)
  br label %loop_increment

odd_branch:
  %9 = load i32, i32* %1, align 4   ;-- load i
  %10 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([11 x i8], [11 x i8]* @"ODD_STR", i32 0, i32 0), i32 %9)
  br label %loop_increment

loop_increment:
  %11 = load i32, i32* %1, align 4  ;-- load i
  %12 = add i32 %11, 1              ;-- increment i
  store i32 %12, i32* %1, align 4   ;-- store i
  br label %loop

exit:
  ret i32 0
}

attributes #0 = { noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }

Output:

0 is even
1 is odd
2 is even
3 is odd

Logo

to even? :num
    output equal? 0 modulo :num 2
end

Logtalk

:- object(even_odd).

    :- public(test_mod/1).
    test_mod(I) :-
        (   I mod 2 =:= 0 ->
            write(even), nl
        ;   write(odd), nl
        ).

    :- public(test_bit/1).
    test_bit(I) :-
        (   I /\ 1 =:= 1 ->
            write(odd), nl
        ;   write(even), nl
        ).

:- end_object.

Output:

| ?- even_odd::test_mod(1).
odd
yes

| ?- even_odd::test_mod(2).
even
yes

| ?- even_odd::test_bit(1).
odd
yes

| ?- even_odd::test_bit(2).
even
yes

LOLCODE

HAI 1.4
I HAS A integer
GIMMEH integer
I HAS A remainder
remainder R MOD OF integer AN 2
BOTH SAEM remainder AN 1, O RLY?
YA RLY
VISIBLE "The integer is odd."
NO WAI
VISIBLE "The integer is even."
OIC 
KTHXBYE

Lua

-- test for even number
if n % 2 == 0 then
  print "The number is even"
end

-- test for odd number
if not (n % 2 == 0) then
  print "The number is odd"
end

M2000 Interpreter

Binary.Add take any numeric type, but value from newer versions can trait as unsigned with range of 0 to 0xFFFFFFFF (so if the number is out of this range, a cut made).

Print binary.and(0xFFFFFFF+10, 0XF)=9 // 0xFFFFFFFF is type Currency and return 4294967295, number 10 is type double so the final number for addition is type double.

Print binary.and(0xFFFFFFF&+10, 0XF)=9 // 0xFFFFFFFF& is type long and return -1, number 10 is type double so the final number for addition is type double.

Print binary.and(0x7FFFFFFF&*16&+10&, 0xF)=15 // 0x7FFFFFFF&*16& cant fit in long so it is type of double 34359738352 (this performed automatic). But if we give this Long A=0x7FFFFFFF&*16& we get an overflow error, because A is a Long, and 34359738352 can't fit.

So Mod if a perfect choice, using it with Decimals (character @ indicate a Decimal type or literal). Variable a take the type of input. There is no reason here to write it as def Odd(a as decimal)= binary.and(Abs(a), 1)=1

Def used to define variables (an error occur if same variable exist), or to define one line local functions. If a function exist then replace code. This is the same for modules/functions, a newer definition alter an old definition with same name, in current module if they are local, or global if they defined as global, like this:

Function Global F(x) { code block here}.

A function F(x) {} is same as

Function F {
      Read x
      code here
}

The same hold for Def Odd(a)=binary.and(Abs(a), 1)=1 Interpreter execute this:

Function Odd {
      Read a
      =binary.and(Abs(a), 1)=1
}

So here is the task. Show an overflow from a decimal, then change function.

Module CheckOdd {
      Def Odd(a)= binary.and(Abs(a), 1)=1
      Print Odd(-5), Odd(6), Odd(11)
      Print Odd(21212121212122122122121@)
      def Odd(a)= Int(Abs(a)) mod 2 =1
      Print Odd(21212121212122122122121@)
      Print Odd(-5), Odd(6), Odd(11)
}
CheckOdd

M4

define(`even', `ifelse(eval(`$1'%2),0,True,False)')
define(`odd',  `ifelse(eval(`$1'%2),0,False,True)')

even(13)
even(8)

odd(5)
odd(0)

Maple

EvenOrOdd := proc( x::integer )
   if x mod 2 = 0 then
      print("Even"):
   else
      print("Odd"):
   end if:
end proc:
EvenOrOdd(9);

"Odd"

Mathematica / Wolfram Language

EvenQ[8]

MATLAB / Octave

Bitwise And:

   isOdd  =  logical(bitand(N,1));
   isEven = ~logical(bitand(N,1));

Remainder of division by two:

   isOdd  =  logical(rem(N,2));
   isEven = ~logical(rem(N,2));

Modulo: 2

   isOdd  =  logical(mod(N,2));
   isEven = ~logical(mod(N,2));

Maxima

evenp(n);
oddp(n);

MAXScript

-- MAXScript : Even or Odd : N.H. 2019
-- Open the MAXScript Listener for input and output
userInt = getKBValue prompt:"Enter an integer and i will tell you if its Even or Odd : "
if classOf userInt != Integer then print "The value you enter must be an integer"
else if (Mod userInt 2) == 0 Then Print "Your number is even"
else Print "Your number is odd"

Mercury

Mercury's 'int' module provides tests for even/odd, along with all the operators that would be otherwise used to implement them.

even(N)  % in a body, suceeeds iff N is even.
odd(N).  % in a body, succeeds iff N is odd.

% rolling our own:
:- pred even(int::in) is semidet.

% It's an error to have all three in one module, mind; even/1 would fail to check as semidet.
even(N) :- N mod 2 = 0.   % using division that truncates towards -infinity
even(N) :- N rem 2 = 0.   % using division that truncates towards zero
even(N) :- N /\ 1 = 0.    % using bit-wise and.

min

Works with: min version 0.19.3

3 even?
4 even?
5 odd?
get-stack print

Output:

(false true true)

MiniScript

for i in range(-4, 4)
    if i % 2 == 0 then print i + " is even" else print i + " is odd"
end for

Output:

-4 is even
-3 is odd
-2 is even
-1 is odd
0 is even
1 is odd
2 is even
3 is odd
4 is even

MIPS Assembly

This uses bitwise AND

.data
	even_str: .asciiz "Even"
	odd_str: .asciiz "Odd"

.text
	#set syscall to get integer from user
	li $v0,5
	syscall

	#perform bitwise AND and store in $a0
	and $a0,$v0,1

	#set syscall to print dytomh
	li $v0,4

	#jump to odd if the result of the AND operation
	beq $a0,1,odd
even:
	#load even_str message, and print
	la $a0,even_str
	syscall

	#exit program
	li $v0,10
	syscall

odd:
	#load odd_str message, and print
	la $a0,odd_str
	syscall

	#exit program
	li $v0,10
	syscall

МК-61/52

/	2	{x}	ЗН

Result: "0" - number is even; "1" - number is odd.

ML

fun even( x: int ) = (x mod 2 = 0);
fun odd( x: int ) = (x mod 2 = 1);

mLite

fun odd
		(x rem 2 = 1) = true
	| 	_ 	      = false
;

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

Modula-2

MODULE EvenOrOdd;
FROM FormatString IMPORT FormatString;
FROM Terminal IMPORT WriteString,ReadChar;

VAR
    buf : ARRAY[0..63] OF CHAR;
    i : INTEGER;
BEGIN
    FOR i:=-5 TO 5 DO
        FormatString("%i is even: %b\n", buf, i, i MOD 2 = 0);
        WriteString(buf)
    END;

    ReadChar
END EvenOrOdd.

Nanoquery

def isEven(n)
        if ((n % 2) = 1)
                return false
        else
                return true
        end
end

for i in range(1, 10)
        print i
        if isEven(i)
                println " is even."
        else
                println " is odd."
        end
end

Output:

1 is odd.
2 is even.
3 is odd.
4 is even.
5 is odd.
6 is even.
7 is odd.
8 is even.
9 is odd.
10 is even.

Neko

var number = 6;

if(number % 2 == 0) {
	$print("Even");
} else {
	$print("Odd");
}

Output:

Even

NESL

NESL provides evenp and oddp functions, but they wouldn't be hard to reimplement.

function even(n) = mod(n, 2) == 0;

% test the function by applying it to the first ten positive integers: %
{even(n) : n in [1:11]};

Output:

it = [F, T, F, T, F, T, F, T, F, T] : [bool]

NetRexx

/* NetRexx */
options replace format comments java crossref symbols nobinary

say 'Val'.right(5)': mod  - ver  - pos  - bits'
say '---'.right(5)': ---- + ---- + ---- + ----'
loop nn = -15 to 15 by 3
  say nn.right(5)':' eo(isEven(nn)) '-' eo(isEven(nn, 'v')) '-' eo(isEven(nn, 'p')) '-' eo(isEven(nn, 'b'))
  end nn
return

-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Overloaded method.  Default is to use the remainder specialization below
method isEven(anInt, meth = 'R') public static returns boolean
  select case meth.upper().left(1)
    when 'R' then eo = isEvenRemainder(anInt)
    when 'V' then eo = isEvenVerify(anInt)
    when 'P' then eo = isEvenPos(anInt)
    when 'B' then eo = isEvenBits(anInt)
    otherwise     eo = isEvenRemainder(anInt) -- default
    end
  return eo

-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
method isEvenRemainder(anInt) public static returns boolean
  return anInt // 2 == 0

-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
method isEvenVerify(anInt) public static returns boolean
  return anInt.right(1).verify('02468') == 0

-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
method isEvenPos(anInt) public static returns boolean
  return '13579'.pos(anInt.right(1)) == 0

-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
method isEvenBits(anInt) public static returns boolean
  return \(anInt.d2x(1).x2b().right(1))

-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
method eo(state = boolean) public static
  if state then sv = 'Even'
           else sv = 'Odd'
  return sv.left(4)

Output:

  Val: mod  - ver  - pos  - bits
  ---: ---- + ---- + ---- + ----
  -15: Odd  - Odd  - Odd  - Odd 
  -12: Even - Even - Even - Even
   -9: Odd  - Odd  - Odd  - Odd 
   -6: Even - Even - Even - Even
   -3: Odd  - Odd  - Odd  - Odd 
    0: Even - Even - Even - Even
    3: Odd  - Odd  - Odd  - Odd 
    6: Even - Even - Even - Even
    9: Odd  - Odd  - Odd  - Odd 
   12: Even - Even - Even - Even
   15: Odd  - Odd  - Odd  - Odd

Never

func isOdd(n : int) -> int {
    n % 2 == 1
}

func isEven(n : int) -> int {
    n % 2 == 0
}

NewLISP

(odd? 1)
(even? 2)

Nim

# Least signficant bit:
proc isOdd(i: int): bool = (i and 1) != 0
proc isEven(i: int): bool = (i and 1) == 0

# Modulo:
proc isOdd2(i: int): bool = (i mod 2) != 0
proc isEven2(i: int): bool = (i mod 2) == 0

# Bit Shifting:
proc isOdd3(n: int): bool = n != ((n shr 1) shl 1)
proc isEven3(n: int): bool = n == ((n shr 1) shl 1)

echo isEven(1)
echo isOdd2(5)

Oberon-2

Works with: oo2c

MODULE EvenOrOdd;
IMPORT
  S := SYSTEM,
  Out;
VAR
  x: INTEGER;
  s: SET;

BEGIN
  x := 10;Out.Int(x,0);
  IF ODD(x) THEN Out.String(" odd") ELSE Out.String(" even") END;
  Out.Ln;

  x := 11;s := S.VAL(SET,LONG(x));Out.Int(x,0);
  IF 0 IN s THEN Out.String(" odd") ELSE Out.String(" even") END;
  Out.Ln;

  x := 12;Out.Int(x,0);
  IF x MOD 2 # 0 THEN Out.String(" odd") ELSE Out.String(" even") END;
  Out.Ln
END EvenOrOdd.

Output:

10 even
11 odd
12 even

Objeck

a := Console->ReadString()->ToInt();
if(a % 2 = 0) {
  "even"->PrintLine();
}
else {
  "odd"->PrintLine();
};

OCaml

Modulo:

let is_even d =
  (d mod 2) = 0

let is_odd d =
  (d mod 2) <> 0

Bitwise and:

let is_even d =
  (d land 1) = 0

let is_odd d =
  (d land 1) <> 0

An instructive view on functional programming and recursion:

(* hmm, only valid for N >= 0 *)
let rec myeven = function
  | 0 -> true
  | 1 -> false
  | n -> myeven (n - 2)

(* and here we have the not function in if form *)
let myodd n = if myeven n then false else true

Oforth

12 isEven
12 isOdd

Ol

Actually, 'even?' and 'odd?' functions are built-in. But,

; 1. Check the least significant bit.
(define (even? i)
   (if (eq? (band i 1) 0) #t #f))
(define (odd? i)
   (if (eq? (band i 1) 1) #t #f))

(print (if (even? 12345678987654321) "even" "odd")) ; ==> odd
(print (if (odd? 12345678987654321) "odd" "even"))  ; ==> odd
(print (if (even? 1234567898765432) "even" "odd"))  ; ==> even
(print (if (odd? 1234567898765432) "odd" "even"))   ; ==> even

; 2. Divide i by 2. The remainder equals 0 iff i is even.
(define (even? i)
   (if (eq? (remainder i 2) 0) #t #f))
(define (odd? i)
   (if (eq? (remainder i 2) 1) #t #f))

(print (if (even? 12345678987654321) "even" "odd")) ; ==> odd
(print (if (odd? 12345678987654321) "odd" "even"))  ; ==> odd
(print (if (even? 1234567898765432) "even" "odd"))  ; ==> even
(print (if (odd? 1234567898765432) "odd" "even"))   ; ==> even

; 3. Use modular congruences. Same as 2.
(define (even? i)
   (if (eq? (mod i 2) 0) #t #f))
(define (odd? i)
   (if (eq? (mod i 2) 1) #t #f))

(print (if (even? 12345678987654321) "even" "odd")) ; ==> odd
(print (if (odd? 12345678987654321) "odd" "even"))  ; ==> odd
(print (if (even? 1234567898765432) "even" "odd"))  ; ==> even
(print (if (odd? 1234567898765432) "odd" "even"))   ; ==> even

OOC

// Using the modulo operator
even: func (n: Int) -> Bool {
  (n % 2) == 0
}

// Using bitwise and
odd: func (n: Int) -> Bool {
  (n & 1) == 1
}

PARI/GP

GP does not have a built-in predicate for testing parity, but it's easy to code:

odd(n)=n%2;

Alternately:

odd(n)=bitand(n,1);

PARI can use the same method as C for testing individual words. For multiprecision integers (t_INT), use mpodd. If the number is known to be nonzero, mod2 is (insignificantly) faster.

Pascal

Built-in boolean function odd:

isOdd := odd(someIntegerNumber);

bitwise and:

function isOdd(Number: integer): boolean
begin
  isOdd := boolean(Number and 1)
end;

Dividing and multiplying by 2 and test on equality:

function isEven(Number: integer): boolean
begin
  isEven := (Number = ((Number div 2) * 2))
end;

Using built-in modulo

function isOdd(Number: integer): boolean
begin
  isOdd := boolean(Number mod 2)
end;

Perl

for(0..10){
    print "$_ is ", qw(even odd)[$_ % 2],"\n";
}

or

print 6 % 2  ? 'odd' : 'even';   # prints even

Phix

There are builtin routines odd() and even() which return true/false - note however they will round non-integer arguments to the nearest whole number, which might be confusing. The mpz_odd() and mpz_even() are similar, but without any way to pass them fractions. In fact odd() invokes and_bits(i,1)=1 and even() invokes and_bits(i,1)=0, so no difference there, and "i&&1" is just shorthand for and_bits(i,1). Lastly remainder(i,2) can also validly be used, however "true" for odd numbers is actually 1 for positive odd integers and -1 for negative odd integers, plus fractions are preserved, so "remainder(i,2)==0" is perhaps for some uses a more flexible and accurate "even"/"not even" test.

with javascript_semantics
include mpfr.e
mpz z = mpz_init()
printf(1," i    odd  even  &&1  rmdr(2)\n")
for i=-5 to 5 do
    mpz_set_si(z,i)
    printf(1,"%2d: %5t %5t %3d %5d\n",{i,odd(i),even(i),i&&1,remainder(i,2)})
end for

Output:

 i    odd  even  &&1  rmdr(2)
-5:  true false   1    -1
-4: false  true   0     0
-3:  true false   1    -1
-2: false  true   0     0
-1:  true false   1    -1
 0: false  true   0     0
 1:  true false   1     1
 2: false  true   0     0
 3:  true false   1     1
 4: false  true   0     0
 5:  true false   1     1

Phixmonti

-5 5 2 tolist for
    dup print " " print 2 mod if "Odd" else "Even" endif print nl
endfor

PHP

// using bitwise and to check least significant digit
echo (2 & 1) ? 'odd' : 'even';
echo (3 & 1) ? 'odd' : 'even';

// using modulo
echo (3 % 2) ? 'odd' : 'even';
echo (4 % 2) ? 'odd' : 'even';

Output:

even
odd
odd
even

Picat

Works with: Picat

% Bitwise and
is_even_bitwise(I) = cond(I /\ 1 == 0, true, false).

% Modulo
is_even_mod(I) = cond(I mod 2 == 0, true, false).

% Remainder
is_even_rem(I) = cond(I rem 2 == 0, true, false).

yes_or_no(B) = YN =>
    B = true, YN = "Yes";
    B = false, YN = "No".

main :-
    foreach (I in 2..3)
        printf("%d is even? %s\n", I, yes_or_no(is_even_bitwise(I))),
        printf("%d is even? %s\n", I, yes_or_no(is_even_mod(I))),
        printf("%d is even? %s\n", I, yes_or_no(is_even_rem(I)))
    end.

Output:

2 is even? Yes
2 is even? Yes
2 is even? Yes
3 is even? No
3 is even? No
3 is even? No

Note: Picat has even/1 and odd/1 as built-ins predicates.

PicoLisp

PicoLisp doesn't have a built-in predicate for that. Using 'bit?' is the easiest and most efficient. The bit test with 1 will return NIL if the number is even.

: (bit? 1 3)
-> 1  # Odd

: (bit? 1 4)
-> NIL  # Even

Pike

> int i = 73;
> (i&1);
Result: 1
> i%2;
Result: 1

PL/I

i = iand(i,1)

The result is 1 when i is odd, and 0 when i is even.

PL/M

In PL/M, even numbers are falsy and odd numbers are truthy, so no explicit test is needed at all.

100H:
BDOS: PROCEDURE (FN, ARG); DECLARE FN BYTE, ARG ADDRESS; GO TO 5; END BDOS;
EXIT: PROCEDURE; CALL BDOS(0,0); END EXIT;
PUT$CHAR: PROCEDURE (CH); DECLARE CH BYTE; CALL BDOS(2, CH); END PUT$CHAR;
PRINT: PROCEDURE (S); DECLARE S ADDRESS; CALL BDOS(9, S); END PRINT;

DECLARE I BYTE;
DO I='0' TO '9';
    CALL PUT$CHAR(I);
    CALL PRINT(.' IS $');
    IF I THEN
        CALL PRINT(.'ODD$');
    ELSE
        CALL PRINT(.'EVEN$');
    CALL PRINT(.(13,10,'$'));
END;

CALL EXIT;
EOF

Output:

0 IS EVEN
1 IS ODD
2 IS EVEN
3 IS ODD
4 IS EVEN
5 IS ODD
6 IS EVEN
7 IS ODD
8 IS EVEN
9 IS ODD

Plain English

The noodle comes with even and odd deciders.

To run:
Start up.
If 56 is even, write "56 is even!" to the console.
If 4 is odd, write "4 is odd!" to the console.
Wait for the escape key.
Shut down.

Output:

56 is even!

PowerShell

Works with: PowerShell version 2

Predicate

A predicate can be used with BigInteger objects. Even/odd predicates to not exist for basic value types. Type accelerator [bigint] can be used in place of [System.Numerics.BigInteger].

$IsOdd  = -not ( [bigint]$N ).IsEven
$IsEven =      ( [bigint]$N ).IsEven

Least significant digit

$IsOdd  = [boolean]( $N -band 1 )
$IsEven = [boolean]( $N -band 0 )

Remainder

Despite being known as a modulus operator, the % operator in PowerShell actually returns a remainder. As such, when testing negative numbers it returns the true modulus result minus M. In this specific case, it returns -1 for odd negative numbers. Thus we test for not zero for odd numbers.

$IsOdd  = $N % 2 -ne 0
$IsEven = $N % 2 -eq 0

Processing

boolean isEven(int i){
  return i%2 == 0;
}

boolean isOdd(int i){
  return i%2 == 1;
}

Prolog

Prolog does not provide special even or odd predicates as one can simply write "0 is N mod 2" to test whether the integer N is even. To illustrate, here is a predicate that can be used both to test whether an integer is even and to generate the non-negative even numbers:

  even(N) :-
     (between(0, inf, N); integer(N) ),
     0 is N mod 2.

Least Significant Bit

If N is a positive integer, then lsb(N) is the offset of its least significant bit, so we could write:

  odd(N) :- N = 0 -> false; 0 is lsb(abs(N)).

Python

Python: Using the least-significant bit method

>>> def is_odd(i): return bool(i & 1)

>>> def is_even(i): return not is_odd(i)

>>> [(j, is_odd(j)) for j in range(10)]
[(0, False), (1, True), (2, False), (3, True), (4, False), (5, True), (6, False), (7, True), (8, False), (9, True)]
>>> [(j, is_even(j)) for j in range(10)]
[(0, True), (1, False), (2, True), (3, False), (4, True), (5, False), (6, True), (7, False), (8, True), (9, False)]
>>>

Python: Using modular congruences

>> def is_even(i):
        return (i % 2) == 0

>>> is_even(1)
False
>>> is_even(2)
True
>>>

Quackery

[ 1 & ]     is odd  ( n --> b )

[ odd not ] is even ( n --> b )

Output:

In the Quackery shell (REPL):

/O> 10 even
... 10 odd
... 11 even
... 11 odd
...

Stack: 1 0 0 1

Quackery: With Anonymous Mutual Recursion

Adapted from the example code at wp:Mutual recursion#Basic examples, with the additional observation that the parity of a negative number is the same as the parity of its absolute value.

See also Mutual recursion#Quackery and Anonymous recursion#Quackery.

  [ abs

    ' [ dup 0 = iff
         [ 2drop true ] done
         1 - this swap rot do ] ( x n --> b )

    ' [ dup 0 = iff
         [ 2drop false ] done
         1 - this swap rot do ] ( x n --> b )

     unrot do ]                 is even ( n --> b )

  11 times
    [ i^ 5 - dup echo
      say " is "
     even iff [ $ "even" ]
     else [ $ "odd" ]
     echo$ say "." cr ]

Output:

-5 is odd.
-4 is even.
-3 is odd.
-2 is even.
-1 is odd.
0 is even.
1 is odd.
2 is even.
3 is odd.
4 is even.
5 is odd.

R

is.even <- function(x) !is.odd(x)

is.odd <- function(x) intToBits(x)[1] == 1
#or
is.odd <- function(x) x %% 2 == 1

Racket

With built in predicates:

(even? 6) ; -> true
(even? 5) ; -> false
(odd? 6) ; -> false
(odd? 5) ; -> true

With modular arithmetic:

(define (my-even? x)
  (= (modulo x 2) 0))

(define (my-odd? x)
  (= (modulo x 2) 1))

With mutually recursive functions:

(define (even-or-odd? i)
  (letrec ([even? (λ (n)
                    (if (= n 0)
                        'even
                        (odd? (sub1 n))))]
           [odd? (λ (n)
                   (if (= n 0)
                       'odd
                       (even? (sub1 n))))])
    (even? i)))

(even-or-odd? 100)  ; => 'even
(even-or-odd? 101)  ; => 'odd

Raku

(formerly Perl 6) Raku doesn't have a built-in for this, but with subsets it's easy to define a predicate for it.

subset Even of Int where * %% 2;
subset Odd of Int where * % 2;

say 1 ~~ Even; # false
say 1 ~~ Odd;  # true
say 1.5 ~~ Odd # false ( 1.5 is not an Int )

Rascal

public bool isEven(int n) = (n % 2) == 0;
public bool isOdd(int n) = (n % 2) == 1;

Or with block quotes:

public bool isEven(int n){return (n % 2) == 0;}
public bool isOdd(int n){return (n % 2) == 1;}

RATFOR

program evenodd

integer a

write(*,101,ADVANCE="NO")
read(*,102)a

if (mod(a,2) .eq. 0) write(*,103)a
   else   write(*,104)a


101  format("Enter a number: ")
102  format(i7)
103  format(i7," Is Even.")
104  format(i7," Is Odd.")


end

Rapira

fun is_even(n)
  return (n /% 2) = 0
end

Red

Red [
    date: 2021-10-24
    red-version: 0.6.4
    description: "Test whether an integer is even or odd."
]

print even? 10 ;== true
print odd? 10 ;== false

ReScript

let is_even = d => mod(d, 2) == 0

let is_odd = d => mod(d, 2) != 0

REXX

Programming note:   division by   1   (one)   in REXX is a way to normalize a number:

• by removing a superfluous leading   +   sign
• by removing superfluous leading zeroes
• by removing superfluous trailing zeroes
• by removing a trailing decimal point
• possible converting an exponentiated number
• possible rounding the number to the current digits

Programming note:   the last method is the fastest method in REXX to determine oddness/evenness.
It requires a sparse stemmed array     !.     be defined in the program's prologue (or elsewhere).
This method gets its speed from   not   using any BIF and   not   performing any (remainder) division.

Some notes on programming styles:   If (execution) speed isn't an issue, then the 1^st test method
shown would be the simplest   (in terms of coding the concisest/tightest/smallest code).   The other test
methods differ mostly in programming techniques, mostly depending on the REXX programmer's style.  
The last method shown is the fastest algorithm, albeit it might be a bit obtuse (without comments) to a
novice reader of the REXX language   (and it requires additional REXX statement baggage).

/*REXX program tests and displays if an integer is  even or odd  using different styles.*/
!.=0;   do j=0  by 2  to 8;   !.j=1;   end       /*assign  0,2,4,6,8  to a "true" value.*/
                                                 /* [↑]  assigns even digits to  "true".*/
numeric digits 1000                              /*handle most huge numbers from the CL.*/
parse arg x _ .                                  /*get an argument from the command line*/
if x==''               then call terr "no integer input (argument)."
if _\=='' | arg()\==1  then call terr "too many arguments: "          _  arg(2)
if \datatype(x, 'N')   then call terr "argument isn't numeric: "      x
if \datatype(x, 'W')   then call terr "argument isn't an integer: "   x
y=abs(x)/1                                       /*in case  X  is negative or malformed,*/
                                                 /* [↑]  remainder of neg # might be -1.*/
                                                 /*malformed #s: 007  9.0  4.8e1  .21e2 */
call tell 'remainder method (oddness)'
if y//2  then say  x  'is odd'
         else say  x  'is even'
                                                 /* [↑]  uses division to get remainder.*/

call tell 'rightmost digit using BIF (not evenness)'
_=right(y, 1)
if pos(_, 86420)==0  then say x 'is odd'
                     else say x 'is even'
                                                 /* [↑]  uses 2 BIF (built─in functions)*/

call tell 'rightmost digit using BIF (evenness)'
_=right(y, 1)
if pos(_, 86420)\==0  then say x 'is even'
                      else say x 'is odd'
                                                 /* [↑]  uses 2 BIF (built─in functions)*/

call tell 'even rightmost digit using array (evenness)'
_=right(y, 1)
if !._  then say x 'is even'
        else say x 'is odd'
                                                 /* [↑]  uses a BIF (built─in function).*/

call tell 'remainder of division via function invoke (evenness)'
if even(y)  then say x 'is even'
            else say x 'is odd'
                                                 /* [↑]  uses (even) function invocation*/

call tell 'remainder of division via function invoke (oddness)'
if odd(y)  then say x 'is odd'
           else say x 'is even'
                                                 /* [↑]  uses (odd)  function invocation*/

call tell 'rightmost digit using BIF (not oddness)'
_=right(y, 1)
if pos(_, 13579)==0  then say x 'is even'
                     else say x 'is odd'
                                                 /* [↑]  uses 2 BIF (built─in functions)*/

call tell 'rightmost (binary) bit (oddness)'
if right(x2b(d2x(y)), 1)  then say x 'is odd'
                          else say x 'is even'
                                                 /* [↑]  requires extra numeric digits. */

call tell 'parse statement using BIF (not oddness)'
parse var  y   ''  -1  _                         /*obtain last decimal digit of the Y #.*/
if pos(_, 02468)==0  then say x 'is odd'
                     else say x 'is even'
                                                 /* [↑]  uses a BIF (built─in function).*/

call tell 'parse statement using array (evenness)'
parse var  y   ''  -1  _                         /*obtain last decimal digit of the Y #.*/
if !._  then say  x  'is even'
        else say  x  'is odd'
                                                 /* [↑]  this is the fastest algorithm. */
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
even:                     return \( arg(1)//2 )  /*returns "evenness" of arg, version 1.*/
even:                     return    arg(1)//2==0 /*   "         "      "  "      "    2.*/
even: parse arg '' -1 _;  return !._             /*   "         "      "  "      "    3.*/
                                                 /*last version shown is the fastest.   */
odd:                      return   arg(1)//2     /*returns  "oddness" of the argument.  */
tell: say;   say center('using the' arg(1), 79, "═");                    return
terr: say;   say '***error***';     say;    say arg(1);    say;          exit 13

output   when using the input of:   0

═════════════════════using the remainder method (oddness)══════════════════════
0 is even

══════════════using the rightmost digit using BIF (not evenness)═══════════════
0 is even

════════════════using the rightmost digit using BIF (evenness)═════════════════
0 is even

═════════════using the even rightmost digit using array (evenness)═════════════
0 is even

════════using the remainder of division via function invoke (evenness)═════════
0 is even

═════════using the remainder of division via function invoke (oddness)═════════
0 is even

═══════════════using the rightmost digit using BIF (not oddness)═══════════════
0 is even

══════════════════using the rightmost (binary) bit (oddness)═══════════════════
0 is even

═══════════════using the parse statement using BIF (not oddness)═══════════════
0 is even

═══════════════using the parse statement using array (evenness)════════════════
0 is even

output   when using the input of:   9876543210987654321098765432109876543210987654321

═════════════════════using the remainder method (oddness)══════════════════════
9876543210987654321098765432109876543210987654321 is odd

   (rest of the output was elided.)

output   when using the input of:   .6821e4

═════════════════════using the remainder method (oddness)══════════════════════
.8621e4 is odd

   (rest of the output was elided.)

output   when using the input of:   -9411

═════════════════════using the remainder method (oddness)══════════════════════
-9411 is odd

   (rest of the output was elided.)

Ring

size = 10
for i = 1 to size
    if i % 2 = 1 see "" + i + " is odd" + nl
    else see "" + i + " is even" + nl ok
next

RPL

To test oddity of real numbers (floating point numbers) :

≪ 2 MOD ≫ ‘ODD?’ STO

To test oddity of binary integers (unsigned integers) :

≪ #1 AND #1 ≠ ≫ ‘BODD?’ STO

To test oddity without caring of the data type :

≪ IF DUP TYPE THEN #1 AND #1 ≠ ELSE 2 MOD END ≫

Input:

47 ODD?
#Fh BODD?

Output:

2: 1
1: 1

Ruby

In Ruby, integers behave like objects, so they respond to methods like : 5.even? resulting to false

print "evens: "
p -5.upto(5).select(&:even?)
print "odds: "
p -5.upto(5).select(&:odd?)

Output:

evens: [-4, -2, 0, 2, 4]
odds: [-5, -3, -1, 1, 3, 5]

Other ways to test even-ness:

n & 1 == 0
quotient, remainder = n.divmod(2); remainder == 0

# The next way only works when n.to_f/2 is exact.
# If Float is IEEE double, then -2**53 .. 2**53 must include n.
n.to_f/2 == n/2

# You can use the bracket operator to access the i'th bit
# of a Fixnum or Bignum (i = 0 means least significant bit)
n[0].zero?

Rust

Checking the least significant digit:

let is_odd = |x: i32| x & 1 == 1;
let is_even = |x: i32| x & 1 == 0;

Using modular congruences:

let is_odd = |x: i32| x % 2 != 0;
let is_even = |x: i32| x % 2 == 0;

Scala

def isEven( v:Int ) : Boolean = v % 2 == 0
def isOdd( v:Int ) : Boolean = v % 2 != 0

Accept any numeric type as an argument:

def isEven( v:Number ) : Boolean = v.longValue % 2 == 0
def isOdd( v:Number ) : Boolean = v.longValue % 2 != 0

Output:

isOdd( 81 )                     // Results in true
isEven( BigInt(378) )           // Results in true
isEven( 234.05003513013145 )    // Results in true

Scheme

even? and odd? functions are built-in (R⁴RS, R⁵RS, and R⁶RS):

> (even? 5)
#f
> (even? 42)
#t
> (odd? 5)
#t
> (odd? 42)
#f

sed

s/[02468]$/& is even/
s/[13579]$/& is odd/

Output:

$ seq -18 7 17 | sed -f even_or_odd.sed                                                                                                                                                                                                                           
-18 is even
-11 is odd
-4 is even
3 is odd
10 is even
17 is odd

Seed7

Test whether an integer or bigInteger is odd:

odd(aNumber)

Test whether an integer or bigInteger is even:

not odd(aNumber)

SenseTalk

set num to random of 100 -- start with a random number from 1 to 100

// use the 'is a' operator to test the value
if num is an odd number then put num & " is odd"

// see if num is divisible by 2
if num is divisible by 2 then put num & " is even (is divisible by 2)"

// check to see if the remainder is 0 when dividing by 2
if num rem 2 is 0 then put num & " is even (zero remainder)"

SequenceL

even(x) := x mod 2 = 0;
odd(x) := x mod 2 = 1;

Output:

cmd:>even(1 ... 10)
[false,true,false,true,false,true,false,true,false,true]
cmd:>odd(1 ... 10)
[true,false,true,false,true,false,true,false,true,false]

SETL

SETL provides built-in even and odd functions. This short program illustrates their use.

xs := {1..10};
evens := {x in xs | even( x )};
odds := {x in xs | odd( x )};
print( evens );
print( odds );

Output:

{2 4 6 8 10}
{1 3 5 7 9}

Shen

Mutual Recursion:

(define even?
    0 -> true
    X -> (odd? (- X 1)))

(define odd?
    0 -> false
    X -> (even? (- X 1)))

Modulo:

(define even? X -> (= 0 (shen.mod X 2)))

(define odd? X -> (not (= 0 (shen.mod X 2))))

Sidef

Built-in methods:

var n = 42;
say n.is_odd;       # false
say n.is_even;      # true

Checking the last significant digit:

func is_odd(n)  { n&1 == 1 };
func is_even(n) { n&1 == 0 };

Using modular congruences:

func is_odd(n)  { n%2 == 1 };
func is_even(n) { n%2 == 0 };

Smalltalk

Using the built in methods on Number class:

5 even
5 odd

even is implemented as follows:

Number>>even
	^((self digitAt: 1) bitAnd: 1) = 0

SNOBOL4

Works with: Macro SNOBOL4 in C

Works with: Spitbol

Works with: SNOBOL4+

      DEFINE('even(n)')                         :(even_end)
even  even = (EQ(REMDR(n, 2), 0) 'even', 'odd') :(RETURN)
even_end

      OUTPUT = "-2 is " even(-2)
      OUTPUT = "-1 is " even(-1)
      OUTPUT = "0 is " even(0)
      OUTPUT = "1 is " even(1)
      OUTPUT = "2 is " even(2)
END

Output:

-2 is even
-1 is odd
0 is even
1 is odd
2 is even

SNUSP

$====!/?\==even#
      - -
#odd==\?/

SPL

> n, 0..9
  ? #.even(n), #.output(n," even")
  ? #.odd(n), #.output(n," odd")
<

Output:

0 even
1 odd
2 even
3 odd
4 even
5 odd
6 even
7 odd
8 even
9 odd

SQL

Database vendors can't agree on how to get a remainder. This should work for many, including Oracle. For others, including MS SQL Server, try "int % 2" instead of "mod(int, 2)".

-- Setup a table with some integers
create table ints(int integer);
insert into ints values (-1);
insert into ints values (0);
insert into ints values (1);
insert into ints values (2);

-- Are they even or odd?
select
  int,
  case mod(int, 2) when 0 then 'Even' else 'Odd' end
from
  ints;

Output:

       INT CASE
---------- ----
        -1 Odd
         0 Even
         1 Odd
         2 Even

SSEM

The SSEM doesn't provide AND, but for once the instruction set does allow the problem to be solved quite elegantly (albeit extravagantly slowly). Load the value of $n$ into storage address 15. The first three instructions test whether $n$ is positive, and replace it with its negation if it isn't. We then loop, subtracting 2 each time and testing whether we have got down either to 0 or to 1. When we have, the computer will halt with the accumulator storing 0 if $n$ was even or 1 if it was odd.

Note that the constant 2, stored at address 14, does double service: it is the operand for the Sub. instruction at address 6 and also the jump target returning to the top of the main loop (which is at address 2 + 1 = 3).

For larger positive or smaller negative values of $n$, you should be ready with something else to do while the machine is working: a test run took several minutes to confirm that 32,769 was odd.

11110000000000100000000000000000   0. -15 to c
00000000000000110000000000000000   1. Test
11110000000001100000000000000000   2. c to 15
11110000000000100000000000000000   3. -15 to c
00001000000001100000000000000000   4. c to 16
00001000000000100000000000000000   5. -16 to c
01110000000000010000000000000000   6. Sub. 14
11110000000001100000000000000000   7. c to 15
10110000000000010000000000000000   8. Sub. 13
00000000000000110000000000000000   9. Test
01110000000000000000000000000000  10. 14 to CI
11110000000000100000000000000000  11. -15 to c
00000000000001110000000000000000  12. Stop
10000000000000000000000000000000  13. 1
01000000000000000000000000000000  14. 2

Standard ML

fun even n =
  n mod 2 = 0;

fun odd n =
  n mod 2 <> 0;

(* bitwise and *)

type werd = Word.word;

fun evenbitw(w: werd) =
  Word.andb(w, 0w2) = 0w0;

fun oddbitw(w: werd) =
  Word.andb(w, 0w2) <> 0w0;

Stata

mata
function iseven(n) {
	return(mod(n,2)==0)
}

function isodd(n) {
	return(mod(n,2)==1)
}
end

Swift

func isEven(n:Int) -> Bool {

    // Bitwise check
    if (n & 1 != 0) {
        return false
    }

    // Mod check
    if (n % 2 != 0) {
        return false
    }
    return true
}

Swift

// Swift has Int.isMultiple(of:Int) -> Bool

var isEven: (_:Int) -> Bool = {$0.isMultiple(of: 2)}

Symsyn

n : 23

 if n bit 0
    'n is odd' []
 else
    'n is even' []

Tcl

package require Tcl 8.5

# Bitwise test is the most efficient
proc tcl::mathfunc::isOdd x  { expr {$x & 1} }
proc tcl::mathfunc::isEven x { expr {!($x & 1)} }

puts " # O E"
puts 24:[expr isOdd(24)],[expr isEven(24)]
puts 49:[expr isOdd(49)],[expr isEven(49)]

Output:

 # O E
24:0,1
49:1,0

TI-57

This routine returns the remainder of the division by 2 of the number in the display register. It is therefore a kind of is_odd(x) function.

Lbl 9
/
2
-
CE
Int
=
×
2
=
INV SBR

TUSCRIPT

$$ MODE TUSCRIPT
LOOP n=-5,5
x=MOD(n,2)
SELECT x
CASE 0
PRINT n," is even"
DEFAULT
PRINT n," is odd"
ENDSELECT
ENDLOOP

Output:

-5 is odd
-4 is even
-3 is odd
-2 is even
-1 is odd
0 is even
1 is odd
2 is even
3 is odd
4 is even
5 is odd 

UNIX Shell

is_even() {
	return $(($1 & 1))
}

Ursa

decl int input
set input (in int console)
if (= (mod input 2) 1)
        out "odd" endl console
else
        out "even" endl console
end if

Output:

123
odd

உயிர்/Uyir

முதன்மை என்பதின் வகை எண் பணி {{
        எ இன் வகை எண்{$5} = 0;
        படை வகை சரம்;

        "எண்ணைக் கொடுங்கள்? ") ஐ திரை.இடு;

        எ = எண்{$5} ஐ விசை.எடு;

        ஒருக்கால் (எ.இருமம்(0) == 1) ஆகில் {
                படை = "ஒற்றை";
        } இல்லையேல் {
                படை = "இரட்டை ";
        }

        {எ, " ஒரு ", படை, "ப்படை எண் ஆகும்"} என்பதை திரை.இடு;

        முதன்மை  = 0;
}};

Verilog

module main;
  integer i;

  initial begin
        for (i = 1; i <= 10; i = i+1) begin
          if (i % 2 == 0) $display(i, " is even");
          else            $display(i, " is odd");
        end
      $finish ;
    end
endmodule

V (Vlang)

fn test(n i64) {
    print('Testing integer $n')

    if n&1 == 0 {
        print(' even')
    }else{
        print('  odd')
    }

    if n%2 == 0 {
        println(' even')
    }else{
        println('  odd')
    }
}

fn main(){
    test(-2)
    test(-1)
    test(0)
    test(1)
    test(2)
}

Output:

Testing integer -2 even even
Testing integer -1  odd  odd
Testing integer 0 even even
Testing integer 1  odd  odd
Testing integer 2 even even

WDTE

let s => import 'stream';
let str => import 'strings';

let evenOrOdd n => (
	let even n => == (% n 2) 0;
	switch n {
		even => 'even';
		default => 'odd';
	};
);

s.range 10
-> s.map (@ s n => str.format '{} is {}.' n (evenOrOdd n))
-> s.map (io.writeln io.stdout)
-> s.drain;

WebAssembly

This solution tests the low bit of the given integer, which is always 0 for even numbers and 1 for odd numbers (including negative numbers).

(module
  ;; function isOdd: returns 1 if its argument is odd, 0 if it is even.
  (func $isOdd (param $n i32) (result i32)
    get_local $n
    i32.const 1
    i32.and   ;; computes (n & 1), i.e. returns low bit of n
  )
  (export "isOdd" (func $isOdd))
)

Wren

Library: Wren-fmt

import "./fmt" for Fmt

var isEven1 = Fn.new { |i| i & 1 == 0 }

var isEven2 = Fn.new { |i| i % 2 == 0 }

var tests = [10, 11, 0,  57,  34,  -23,  -42]
System.print("Tests    : %(Fmt.v("s", -4, tests, 0, " ", ""))")
var res1 = tests.map { |t| isEven1.call(t) ? "even" : "odd" }.toList
System.print("Method 1 : %(Fmt.v("s", -4, res1, 0, " ", ""))")
var res2 = tests.map { |t| isEven2.call(t) ? "even" : "odd" }.toList
System.print("Method 2 : %(Fmt.v("s", -4, res2, 0, " ", ""))")

Output:

Tests    : 10   11   0    57   34   -23  -42 
Method 1 : even odd  even odd  even odd  even
Method 2 : even odd  even odd  even odd  even

x86-64 Assembly

evenOdd:
mov  rax,1
and  rax,rdi
ret

XBS

#>
Typed XBS
evenOrOdd function
true = even
false = odd
<#
func evenOrOdd(a:number=0){
	send a%2==0;
}
set arr:array = [0,1,2,3,4,5,6,7,9,10];
foreach(v of arr){
	log(v+" is even? "+evenOrOdd(v))
}

Output:

0 is even? true
1 is even? false
2 is even? true
3 is even? false
4 is even? true
5 is even? false
6 is even? true
7 is even? false
9 is even? false
10 is even? true

xEec

>100 p i# jz-1 o# t h#1 ms jz2003 p >0110 h#2 r ms t h#1 ms p 
jz1002 h? jz2003 p jn0110 h#10 o$ p jn100 >2003 p p h#0 h#10 
h$d h$d h$o h#32 h$s h$i h#32 jn0000 >1002 p p h#0 h#10 
h$n h$e h$v h$e h#32 h$s h$i h#32 >0000 o$ p jn0000 jz100

XLISP

XLISP provides EVENP and ODDP, or, if you prefer, EVEN? and ODD?; if one wanted to reimplement them, it could be done like this (or in other ways).

(defun my-evenp (x)
    (= (logand x 1) 0) )

(defun my-oddp (x)
    (/= (logand x 1) 0) )

Xojo

For num As Integer = 1 To 5
  If num Mod 2 = 0 Then
    MsgBox(Str(num) + " is even.")
  Else
    MsgBox(Str(num) + " is odd.")
  End If
Next

Output:

1 is odd.
2 is even.
3 is odd.
4 is even.
5 is odd.

XPL0

include c:\cxpl\codes;
int I;
[for I:= -4 to +3 do
        [IntOut(0, I);
        Text(0, if I&1 then " is odd   " else " is even  ");
        Text(0, if rem(I/2)#0 then "odd" else "even");
        CrLf(0);
        ];
]

Output:

-4 is even  even
-3 is odd   odd
-2 is even  even
-1 is odd   odd
0 is even  even
1 is odd   odd
2 is even  even
3 is odd   odd

Z80 Assembly

Z80 Assembly has a few ways of testing if a number is even or odd:

RRC

A right rotate will set the carry if the register's value is odd and clear it if it's even. This does alter the contents of the register, so only use this method if you don't need to remember the number being tested after getting the results of the test. This is the fastest way the Z80 can test a value for even or odd, but only when testing the accumulator A

rrca
jp nc,isEven

SRA/SRL

In similar vein, there are also shift instructions. The arithmetic shift instruction retains the sign bit (bit 7) of the operand in question, while the logical shift sets bit 7 to 0.

sra a
jp nc,isEven

AND

AND 1 will change the accumulator to 1 if its value was odd, and 0 if its value was even. If you want to selectively load a 0 or 1 into the accumulator based on whether a variable is odd or even, this is the best way to do so. Like the RRC method, this test is destructive, so if you need to preserve the original value of the accumulator after the test, use the method below instead.

and &01
jp z,isEven

BIT

This method is the slowest, but it doesn't change the value in the register being tested. It works on any 8 bit register, (HL), (IX+#), or (IY+#), making it the most versatile. Although I say it's the slowest, the difference is so small and the execution time so fast that you'd never notice anyway. The Z80 can perform all these tests faster than you can blink!

bit 0,c
jp z,C_IS_EVEN

zkl

[-3..4].pump(fcn(n){ println(n," is ",n.isEven and "even" or "odd") })

Ints have isEven and isOdd properties. pump, in this case, is the same as apply/map without aggregating a result.

Output:

-3 is odd
-2 is even
-1 is odd
0 is even
1 is odd
2 is even
3 is odd
4 is even

[-3..4].apply("isEven").println();

Output:

L(False,True,False,True,False,True,False,True)

Zoea

program: even_or_odd 
  case: 1
        input: 2 
        output: even 
  case: 2 
        input: 4 
        output: even 
  case: 3 
        input: 1 
        output: odd 
  case: 4 
        input: 7 
        output: odd

Zoea Visual

Even or odd

zonnon

module Main;
var
	x: integer;
	s: set;
begin
	x := 10;writeln(x:3," is odd?",odd(x));
	s := set(s);writeln(x:3," is odd?",0 in s); (* check right bit *)
	x := 11;writeln(x:3," is odd?",odd(x));
	s := set(x);writeln(x:3," is odd?",0 in s); (* check right bit *)
end Main.

Output:

 10 is odd? false
 10 is odd? false
 11 is odd?  true
 11 is odd?  true