I'm working on modernizing Rosetta Code's infrastructure. Starting with communications. Please accept this time-limited open invite to RC's Slack.. --Michael Mol (talk) 20:59, 30 May 2020 (UTC)

# Luhn test of credit card numbers

(Redirected from Luhn test)
Luhn test of credit card numbers
You are encouraged to solve this task according to the task description, using any language you may know.

The Luhn test is used by some credit card companies to distinguish valid credit card numbers from what could be a random selection of digits.

Those companies using credit card numbers that can be validated by the Luhn test have numbers that pass the following test:

1. Reverse the order of the digits in the number.
2. Take the first, third, ... and every other odd digit in the reversed digits and sum them to form the partial sum s1
3. Taking the second, fourth ... and every other even digit in the reversed digits:
1. Multiply each digit by two and sum the digits if the answer is greater than nine to form partial sums for the even digits
2. Sum the partial sums of the even digits to form s2
1. If s1 + s2 ends in zero then the original number is in the form of a valid credit card number as verified by the Luhn test.

For example, if the trial number is 49927398716:

Reverse the digits:
61789372994
Sum the odd digits:
6 + 7 + 9 + 7 + 9 + 4 = 42 = s1
The even digits:
1,  8,  3,  2,  9
Two times each even digit:
2, 16,  6,  4, 18
Sum the digits of each multiplication:
2,  7,  6,  4,  9
Sum the last:
2 + 7 + 6 + 4 + 9 = 28 = s2

s1 + s2 = 70 which ends in zero which means that 49927398716 passes the Luhn test

Write a function/method/procedure/subroutine that will validate a number with the Luhn test, and
use it to validate the following numbers:

   49927398716
49927398717
1234567812345678
1234567812345670


## 11l

Translation of: Python
F luhn(n)   V ch = String(n)   V sum = 0   V chParity = ch.len % 2   L(i) (ch.len-1 .. 0).step(-1)      V j = Int(ch[i])      I (i + 1) % 2 != chParity         j *= 2         I j > 9            j -= 9      sum += j   R sum % 10 == 0 L(n) (49927398716,      49927398717,      1234567812345678,      1234567812345670)   print(luhn(n))
Output:
1B
0B
0B
1B


## 360 Assembly

Translation of: VBScript

For maximum compatibility, this program uses only the basic instruction set (S/360) and an ASSIST macro (XPRNT) to keep the code as short as possible.

*        Luhn test of credit card numbers        22/05/2016LUHNTEST CSECT         USING  LUHNTEST,R13       base register         B      72(R15)            skip savearea         DC     17F'0'             savearea         STM    R14,R12,12(R13)    prolog         ST     R13,4(R15)         "         ST     R15,8(R13)         "         LR     R13,R15            "         LA     R9,T               @t(k)         LA     R8,N               for nLOOPK    EQU    *                  for k=1 to n         LR     R4,R9              @t(k),@s[1]         LA     R6,1               from i=1         LA     R7,M               to mLOOPI1   CR     R6,R7              for i=1 to m         BH     ELOOPI1            leave i         CLI    0(R4),C' '           if mid(s,i,1)=" "         BNE    ITERI1               then         BCTR   R6,0                   i-1         ST     R6,L                   l=i-1         B      ELOOPI1                exit for*                                    end ifITERI1   LA     R4,1(R4)             next @s[i]         LA     R6,1(R6)             i=i+1         B      LOOPI1             next iELOOPI1  EQU    *                  out of loop i         MVC    W,BLANK            w=" "         LA     R4,W               [email protected]         LR     R5,R9              [email protected]         A      R5,L               [email protected]+l         BCTR   R5,0               is=s+l-1         L      R6,L               i=l         LA     R7,1               to 1LOOPI2   CR     R6,R7              for i=l to 1 by -1          BL     ELOOPI2            leave i         MVC    0(1,R4),0(R5)        mid(w,iw,1)=mid(s,is,1)         LA     R4,1(R4)             iw=iw+1         BCTR   R5,0                 is=is-1         BCTR   R6,0                 i=i-1         B      LOOPI2             next iELOOPI2  EQU    *                  out of loop i         LA     R11,0              s1=0         LA     R12,0              s2=0         LA     R6,1               i=1         L      R7,L               to lLOOPI3   CR     R6,R7              for i=1 to l         BH     ELOOPI3            leave i         LA     R2,W-1             @w-1         AR     R2,R6              w[i]         MVC    CI,0(R2)           ci=mid(w,i,1)         NI     CI,X'0F'           zap upper half byte         LR     R4,R6              i         SRDA   R4,32              >>32         D      R4,=F'2'           i/2         LTR    R4,R4              if mod(i,2)>0         BNH    NOTMOD             then         XR     R2,R2                clear         IC     R2,CI                z=cint(mid(w,i,1))         AR     R11,R2               s1=s1+cint(mid(w,i,1))         B      EIFMOD             elseNOTMOD   XR     R2,R2                clear         IC     R2,CI                cint(mid(w,i,1))         SLA    R2,1                 *2         ST     R2,Z                 z=cint(mid(w,i,1))*2         C      R2,=F'10'            if z<10         BNL    GE10                 then         A      R12,Z                  s2=s2+z         B      EIF10                elseGE10     L      R2,Z                   z         CVD    R2,PL8                 binary to packed         UNPK   CL16,PL8               packed to zoned         OI     CL16+15,X'F0'          zoned to char (zap sign)         MVC    X(1),CL16+15           x=right(cstr(z),1)         NI     X,X'0F'                zap upper half byte         XR     R2,R2                  r2=0         IC     R2,X                   r2=cint(right(cstr(z),1))         AR     R12,R2                 s2=s2+r2         LA     R12,1(R12)             s2=s2+cint(right(cstr(z),1))+1EIF10    EQU    *                    end ifEIFMOD   EQU    *                  end if         LA     R6,1(R6)           i=i+1         B      LOOPI3             next iELOOPI3  EQU    *                  out of loop i         LR     R1,R11             s1         AR     R1,R12             s1+s2         CVD    R1,PL8             binary to packed         UNPK   CL16,PL8           packed to zoned         CLI    CL16+15,X'C0'      if right(cstr(s1+s2),1)="0"         BNE    NOTZERO            then         MVC    R,=CL8'Valid'        r="Valid"         B      ECLI               elseNOTZERO  MVC    R,=CL8'Invalid'      r="Invalid"ECLI     EQU    *                  end if         MVC    PG(M),0(R9)        t(k)         MVC    PG+M+1(L'R),R      r         XPRNT  PG,L'PG            print buffer         LA     R9,M(R9)           at=at+m         BCT    R8,LOOPK           next k         L      R13,4(0,R13)       epilog         LM     R14,R12,12(R13)    "         XR     R15,R15            "         BR     R14                exitN        EQU    (TEND-T)/L'TM        EQU    20T        DC     CL(M)'49927398716         '         DC     CL(M)'49927398717         '         DC     CL(M)'1234567812345678    '         DC     CL(M)'1234567812345670    'TEND     DS     0CW        DS     CL(M)BLANK    DC     CL(M)' 'L        DS     FZ        DS     FPL8      DS     PL8 CL16     DS     CL16CI       DS     CX        DS     CR        DS     CL8PG       DC     CL80' '            buffer         YREGS         END    LUHNTEST
Output:
49927398716          Valid
49927398717          Invalid
1234567812345678     Invalid
1234567812345670     Valid


## 8080 Assembly

	org	100h	jmp 	demo	;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;	;;;	Check if the 0-terminated string at HL passes the Luhn test.	;;;	Returns with carry clear if the string passes, carry set	;;;	if the string fails. luhn:	mvi	b,0	; Counter	mov	d,b	; D = S1+S2 (we don't need to keep them separate)lscan:	mov	a,m	; Get byte 	inx 	h	; Increment pointer	inr	b	; Increment counter	ana	a	; Is it 0?	jnz	lscan	; If not, try next byte	dcx	h	; Go to the byte before the 0	dcx	h	dcr	b	; Decrement counter	rz		; If 0, the string was empty, return.lloop:	mvi	c,'0'	; ASCII zero	mov	a,d	; Add odd digit to the total 	add	m	sub	c	; Subtract ASCII zero	mov	d,a	dcr	b	; If last digit, we're done	jz	ldone	dcx	h	; Go back one byte	mov	a,m	; Get even digit	sub	c	; Subtract ASCII zero	add	a	; Multiply by two	mvi	c,9	; 10-1, compensate for extra subtraction loopldiv:	inr	c	; Find two digits using trial subtraction	sui	10			jnc	ldiv	add	c	; Add the possible second digit in	add	d	; Add it to the total	mov	d,a	dcx	h	; Go back one byte	dcr	b	; Done yet?	jnz	lloopldone:	mov	a,d	; See if total is divisible by 10	mvi	b,10lchk:	sub	b	; Trial subtraction, subtract 10	rz		; If zero, it is divisible, return (carry clear)	rc		; If carry, it is not divisible, return (carry set)	jmp	lchk	;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;	;;;	Run the routine on the argument given on the CP/M command linedemo:	lxi	h,80h	; Zero-terminate the command line argument	mov	a,m 	add	l	mov	l,a	inr	l	mvi	m,0	mvi	l,82h	; Run the 'luhn' subroutine	call 	luhn	mvi	c,9	lxi	d,pass	; Carry clear = print 'Pass'	jnc	5	lxi	d,fail	; Carry set = print 'Fail'	jmp	5pass:	db	'Pass$'fail: db 'Fail$'
Output:
A>luhn 49927398716
Pass
A>luhn 49927398717
Fail
A>luhn 1234567812345678
Fail
A>luhn 1234567812345670
Pass

## 8086 Assembly

	bits	16	cpu	8086	org	100hsection	.text	jmp	demo		;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;	;;; 	Check whether the 0-terminated string at DS:SI passes the Luhn	;;; 	test. Returns with carry clear if the string passes, carry	;;;	set if the string fails.luhn:	push	es	; Keep original ES, and set ES=DS so SCASB can be used.	push	ds	; "REP DS:SCASB" is a bad idea, because the 286 has a	pop	es	; bug where it "forgets" the 2nd prefix if interrupted!	mov	di,si	; DI = pointer	xor	ax,ax	; Zero to test against	xor	bl,bl	; BL = S1+S2	mov	dx,0A30h	; DH = 10 (divisor), DL = '0' (ASCII zero)  	xor	cx,cx	; Set counter to 65535	dec	cx	cld		; Seek forwards	repnz	scasb	; Find zero	dec	di	; SCASB goes one byte too far	xchg	si,di	; SI = pointer, DI = end (or rather, beginning)	mov	cx,si	; CX = counter	sub	cx,di	jcxz	.done	; Empty string = stop	dec	si	; We don't need the zero itself	std		; Seek backwards.loop:	lodsb		; Get number in odd position	sub	al,dl	; Subtract ASCII zero	add	bl,al	; Add to total	dec	cx	; One fewer character	jz	.done	; No more characters = stop	lodsb		; Get number in even position	sub	al,dl	; Subtract ASCII zero	add	al,al	; Multiply by two	xor	ah,ah	; AX = AL 	div	dh	; Divide by 10; AL=quotient, AH=remainder	add	al,ah	; Add the two "digits" together	add	bl,al	; Add to total	loop 	.loop	; Decrement CX and loop.done:	xor	ah,ah	; Divide total by 10	mov	al,bl	div	dh	and	ah,ah	; If remainder 0, then return with carry clear	jz	.out	stc		; Set carry (remainder wasn't 0, the test failed).out:	cld		; Clean up: clear direction flag,	pop	es	; and restore ES.	ret 	;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;	;;;	Run the 'luhn' routine on the argument given on the MS-DOS	;;;	command line. demo:	mov	si,80h			; Zero-terminate the argument	xor	bh,bh	mov	bl,[si]	mov	[si+bx+1],bh	inc	si	inc	si	call 	luhn			; Call the routine	mov	ah,9	mov	dx,pass			; If carry is clear, print 'Pass'	jnc	print	mov	dx,fail			; Otherwise, print 'fail'print:	int	21h	retsection	.datapass:	db	'Pass$'fail: db 'Fail$'
Output:
C:\>luhn86 49927398716
Pass
C:\>luhn86 49927398717
Fail
C:\>luhn86 1234567812345678
Fail
C:\>luhn86 1234567812345670
Pass

## 8th

 \ Adapted from the C version:: remap \ n1 -- n2  [0,2,4,6,8,1,3,5,7,9]  swap caseof ; : luhn \ s -- f  0 swap  s:rev  (    '0 n:-    swap 2 n:mod if remap then    n:+  ) s:each   10 n:mod not ; : test-luhn \ s --  dup . space  luhn if "OK" else "FAIL" then . cr ; "49927398716" test-luhn"49927398717" test-luhn "1234567812345678" test-luhn"1234567812345670" test-luhn bye
Output:
49927398716 OK
49927398717 FAIL
1234567812345678 FAIL
1234567812345670 OK


## ABAP

METHOD luhn_check.   DATA: sum(1) TYPE n VALUE 0. " Sum of checksum.  DATA: current TYPE i. " Current digit.  DATA: odd TYPE i VALUE 1. " Multiplier.  DATA: len TYPE i. " String crowler.    " Luhn algorithm.  len = NUMOFCHAR( pi_string ) - 1.  WHILE ( len >= 0 ).    current = pi_string+len(1) * odd.    IF ( current > 9 ).      current = current - 9. " Digits sum.    ENDIF.    sum = sum + current.    odd = 3 - odd. " 1 <--> 2 Swich    len = len - 1. " Move to next charcter.  ENDWHILE.   " Validation check.  IF ( sum = 0 ).    pr_valid = abap_true.  ELSE.    pr_valid = abap_false.  ENDIF. ENDMETHOD.

## ACL2

(include-book "arithmetic-3/top" :dir :system) (defun digits (n)   (if (zp n)       nil       (cons (mod n 10)             (digits (floor n 10))))) (defun sum (xs)   (if (endp xs)       0       (+ (first xs)          (sum (rest xs))))) (defun double-and-sum-digits (xs)   (if (endp xs)       nil       (cons (sum (digits (* 2 (first xs))))             (double-and-sum-digits (rest xs))))) (defun dmx (xs)   (if (endp (rest xs))       (mv xs nil)       (mv-let (odds evens)               (dmx (rest (rest xs)))          (mv (cons (first xs) odds)              (cons (second xs) evens))))) (defun luhn (n)   (mv-let (odds evens)           (dmx (digits n))      (= (mod (+ (sum odds)                 (sum (double-and-sum-digits evens)))              10)         0)))
Output:
> (luhn 49927398716)
T
> (luhn 49927398717)
NIL
> (luhn 1234567812345678)
NIL
> (luhn 1234567812345670)
T

## Action!

PROC ReverseDigits(CHAR ARRAY n,rev)  BYTE i,j   i=n(0)  WHILE i>0 AND n(i)='0  DO    i==-1  OD   j=1  WHILE i>0  DO    rev(j)=n(i)    j==+1 i==-1  OD  rev(0)=j-1RETURN BYTE FUNC SumOddDigits(CHAR ARRAY n)  BYTE sum,i   sum=0  FOR i=1 TO n(0) STEP 2  DO    sum==+ValB(n(i))  ODRETURN(sum) BYTE FUNC SumEvenDigitsMultiplied(CHAR ARRAY n)  BYTE sum,i,v   sum=0  FOR i=2 TO n(0) STEP 2  DO    v=ValB(n(i))*2    IF v>9 THEN v==-9 FI    sum==+v  ODRETURN(sum) BYTE FUNC Luhn(CHAR ARRAY n)  CHAR ARRAY rev(20)  BYTE s1,s2   ReverseDigits(n,rev)  s1=SumOddDigits(rev)  s2=SumEvenDigitsMultiplied(rev)   IF (s1+s2) MOD 10=0 THEN    RETURN(1)  FIRETURN(0) PROC Test(CHAR ARRAY n)  PrintF("%S is ",n)  IF Luhn(n) THEN    PrintE("valid")  ELSE    PrintE("invalid")  FIRETURN PROC Main()  Test("49927398716")  Test("49927398717")  Test("1234567812345678")  Test("1234567812345670")RETURN
Output:
49927398716 is valid
49927398717 is invalid
1234567812345678 is invalid
1234567812345670 is valid


## ActionScript

function isValid(numString:String):Boolean{	var isOdd:Boolean = true;	var oddSum:uint = 0;	var evenSum:uint = 0;	for(var i:int = numString.length - 1; i >= 0; i--)	{		var digit:uint = uint(numString.charAt(i))		if(isOdd) oddSum += digit;		else evenSum += digit/5 + (2*digit) % 10;		isOdd = !isOdd;	}	if((oddSum + evenSum) % 10 == 0) return true; 	return false;} trace(isValid("49927398716"));trace(isValid("49927398717"));trace(isValid("1234567812345678"));trace(isValid("1234567812345670"));

Translation of: C
Works with: GNAT
with Ada.Text_IO;use  Ada.Text_IO; procedure Luhn is   function Luhn_Test (Number: String) return Boolean is    Sum  : Natural := 0;    Odd  : Boolean := True;    Digit: Natural range 0 .. 9;  begin    for p in reverse Number'Range loop      Digit := Integer'Value (Number (p..p));      if Odd then        Sum := Sum + Digit;      else        Sum := Sum + (Digit*2 mod 10) + (Digit / 5);      end if;      Odd := not Odd;    end loop;    return (Sum mod 10) = 0;  end Luhn_Test; begin   Put_Line (Boolean'Image (Luhn_Test ("49927398716")));  Put_Line (Boolean'Image (Luhn_Test ("49927398717")));  Put_Line (Boolean'Image (Luhn_Test ("1234567812345678")));  Put_Line (Boolean'Image (Luhn_Test ("1234567812345670"))); end Luhn;
Output:
TRUE
FALSE
FALSE
TRUE


## ALGOL 68

Translation of: C++ – Note: This specimen retains the original C coding style.
Works with: ALGOL 68 version Standard - no extensions to language used
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny
Works with: ELLA ALGOL 68 version Any (with appropriate job cards)
PROC to int = (CHAR c)INT:    ABS c - ABS "0"; PROC confirm = (STRING id)BOOL:(    BOOL is odd digit := TRUE;    INT s := 0;    STRING cp;     FOR cp key FROM UPB id BY -1 TO LWB id DO        INT k := to int(id[cp key]);        s +:=             IF is odd digit THEN k            ELIF k /= 9 THEN 2*k MOD 9             ELSE 9            FI;        is odd digit := NOT is odd digit    OD;    0 = s MOD 10); main:(    []STRING t cases = (        "49927398716",        "49927398717",        "1234567812345678",        "1234567812345670"    );    FOR cp key TO UPB t cases DO        STRING cp = t cases[cp key];        print((cp, ": ", confirm(cp), new line))    OD)
Output:
49927398716: T
49927398717: F
1234567812345678: F
1234567812345670: T


## ALGOL W

Separate source so the LuhnTest procedure can be used in other tasks, e.g.: Validate International Securities Identification Number

% returns true if ccNumber passes the Luhn test, false otherwise %% as Algol W has fixed length strings, the length of the number  %% must be specified in ccLength                                  %logical procedure LuhnTest ( string(32) value ccNumber                           ; integer    value ccLength                           ) ;begin    integer checkSum;    logical oddDigit, isValid;    checkSum := 0;    isValid := oddDigit := true;    for cPos := ccLength step -1 until 1 do begin        integer digit;        digit := decode( ccNumber( cPos - 1 // 1 ) ) - decode( "0" );        if digit < 0 or digit > 9 then isValid := false        else if oddDigit        then checkSum := checkSum + digit        else checkSum := checkSum + ( case digit + 1 of ( 0, 2, 4, 6, 8                                                        , 1, 3, 5, 7, 9                                                        )                                    );        oddDigit := not oddDigit    end for_cPos ;    isValid and ( ( checkSum rem 10 ) = 0 )end LuhnTest

Use the above to test the LuhnTest procedure:

begin    % external procedure that returns true if ccNumber passes the Luhn test, false otherwise %    logical procedure LuhnTest ( string(32) value ccNumber                               ; integer    value ccLength                               ) ; algol "LUHN" ;      % task test cases %     procedure testLuhnTest ( string(32) value ccNumber                           ; integer    value ccLength                           ) ;        write( s_w := 0, ccNumber, if LuhnTest( ccNumber, ccLength ) then " is valid" else " is invalid" );     testLuhnTest( "49927398716",      11 );    testLuhnTest( "49927398717",      11 );    testLuhnTest( "1234567812345678", 16 );    testLuhnTest( "1234567812345670", 16 ) end.
Output:
49927398716                      is valid
49927398717                      is invalid
1234567812345678                 is invalid
1234567812345670                 is valid


## APL

Works with: Dyalog APL
LuhnTest←{                                                                                   digits←⍎¨⍵                       ⍝ Characters to digits                        doubled←2∘×@(⌽⍤~1 0⍴⍨≢)⊢digits   ⍝ Double every other digit                    partial←-∘[email protected](9∘<)⊢doubled        ⍝ Subtract 9 is equivalent to sum of digits for the domain 10≤x≤19     0=10|+/partial                   ⍝ Valid if sum is a multiple of 10        }
Output:
      LuhnTest¨'49927398716' '49927398717' '1234567812345678' '1234567812345670'
1 0 0 1

Works with: APL+Win
    ∇ ret←LuhnTest num;s1;s2[1]   num←⌽((⌈10⍟num)/10)⊤num[2]   s1←+/((⍴num)⍴1 0)/num[3]   s2←+/∊(⊂10 10)⊤¨2×((⍴num)⍴0 1)/num[4]   ret←0=10⊤s1+s2    ∇
Output:
      LuhnTest¨ 49927398716 49927398717 1234567812345678 1234567812345670
1 0 0 1


## AppleScript

### Functional

-- luhn :: String -> Boolon luhn(s)    -- True if the digit string represents    -- a valid Luhn credit card number.     script divMod10Sum        on |λ|(a, x)            a + x div 10 + x mod 10        end |λ|    end script     0 = foldl(divMod10Sum, 0, ¬        zipWith(my mul, ¬            map(my int, reverse of (characters of s)), ¬            cycle({1, 2}))) mod 10end luhn  --------------------------- TEST ---------------------------on run    map(luhn, ¬        {"49927398716", "49927398717", ¬            "1234567812345678", "1234567812345670"})     --> {true, false, false, true}end run  ---------------- REUSABLE GENERIC FUNCTIONS ---------------- -- cycle :: [a] -> Generator [a]on cycle(xs)    script        property lng : 1 + (length of xs)        property i : missing value        on |λ|()            if missing value is i then                set i to 1            else                set nxt to (1 + i) mod lng                if 0 = ((1 + i) mod lng) then                    set i to 1                else                    set i to nxt                end if            end if            return item i of xs        end |λ|    end scriptend cycle -- foldl :: (a -> b -> a) -> a -> [b] -> aon foldl(f, startValue, xs)    tell mReturn(f)        set v to startValue        set lng to length of xs        repeat with i from 1 to lng            set v to |λ|(v, item i of xs, i, xs)        end repeat        return v    end tellend foldl -- int :: String -> Inton int(s)    s as integerend int -- length :: [a] -> Inton |length|(xs)    set c to class of xs    if list is c or string is c then        length of xs    else        (2 ^ 29 - 1) -- (maxInt - simple proxy for non-finite)    end ifend |length| -- 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 ifend mReturn -- map :: (a -> b) -> [a] -> [b]on map(f, xs)    -- The list obtained by applying f    -- to each element of xs.    tell mReturn(f)        set lng to length of xs        set lst to {}        repeat with i from 1 to lng            set end of lst to |λ|(item i of xs, i, xs)        end repeat        return lst    end tellend map -- min :: Ord a => a -> a -> aon min(x, y)    if y < x then        y    else        x    end ifend min -- mul (*) :: Num a => a -> a -> aon mul(a, b)    a * bend mul -- take :: Int -> [a] -> [a]-- take :: Int -> String -> Stringon take(n, xs)    set c to class of xs    if list is c then        if 0 < n then            items 1 thru min(n, length of xs) of xs        else            {}        end if    else if string is c then        if 0 < n then            text 1 thru min(n, length of xs) of xs        else            ""        end if    else if script is c then        set ys to {}        repeat with i from 1 to n            set v to |λ|() of xs            if missing value is v then                return ys            else                set end of ys to v            end if        end repeat        return ys    else        missing value    end ifend take -- zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]on zipWith(f, xs, ys)    set lng to min(|length|(xs), |length|(ys))    if 1 > lng then return {}    set xs_ to take(lng, xs) -- Allow for non-finite    set ys_ to take(lng, ys) -- generators like cycle etc    set lst to {}    tell mReturn(f)        repeat with i from 1 to lng            set end of lst to |λ|(item i of xs_, item i of ys_)        end repeat        return lst    end tellend zipWith
Output:
{true, false, false, true}

### Straightforward

on luhnTest(n)    -- Accept only text input.    if (n's class is not text) then return false    -- Edit out any spaces or dashes.    set astid to AppleScript's text item delimiters    set AppleScript's text item delimiters to {space, "-"}    set n to n's text items    set AppleScript's text item delimiters to ""    set n to n as text    set AppleScript's text item delimiters to astid    -- Check that what's left is numeric.    try        n as number    on error        return false    end try     -- Do the calculation two digits at a time, starting at the end of the text and working back.    set sum to 0    repeat with i from ((count n) - 1) to 1 by -2        set n2 to (text i thru (i + 1) of n) as integer        tell n2 div 10 mod 10 * 2 to set sum to sum + it div 10 + it mod 10 + n2 mod 10    end repeat    -- If there's an odd digit left over, add that in too.    if (i is 2) then set sum to sum + (character 1 of n)     return (sum mod 10 is 0)end luhnTest -- Test code:set testResults to {}repeat with testNumber in {"49927398716", "49927398717", "1234567812345678", "1234567812345670"}    set end of testResults to {testNumber:testNumber's contents, valid:luhnTest(testNumber)}end repeatreturn testResults
Output:
{{testNumber:"49927398716", valid:true}, {testNumber:"49927398717", valid:false}, {testNumber:"1234567812345678", valid:false}, {testNumber:"1234567812345670", valid:true}}

## ARM Assembly

.text.global _start_start:    ldr r0, =example_numbers    bl test_number     add r1, r0, #1    bl length    add r0, r1, r0    bl test_number     add r1, r0, #1    bl length    add r0, r1, r0    bl test_number     add r1, r0, #1    bl length    add r0, r1, r0    bl test_number     mov r0, #0    mov r7, #1    swi 0 test_number:    push {r0, lr}    bl print_string     bl luhn_test    cmp r0, #1    ldreq r0, =valid_message    ldrne r0, =invalid_message    bl print_string    pop {r0, lr}    mov pc, lr   print_string:    push {r0-r7, lr}    mov r1, r0   @ string to print    bl length    mov r2, r0   @ length of string    mov r0, #1   @ write to stdout    mov r7, #4   @ SYS_WRITE    swi 0        @ call system interupt    pop {r0-r7, lr}    mov pc, lr @ r0 address of credit card number string@ returns result in r0luhn_test:    push {r1-r7, lr}    mov r1, r0    bl isNumerical            @ check if string is a number    cmp r0, #1    bne .luhn_test_end        @ exit if not number    mov r0, r1     ldr r1, =reversed_string  @ address to store reversed string    bl reverse                @ reverse string    push {r0}    bl length   @ get length of string    mov r4, r0  @ store string length in r4     pop {r0}    mov r2, #0  @ string index    mov r6, #0  @ sum of odd digits    mov r7, #0  @ sum of even digits    .loadNext:        ldrb r3, [r1, r2]         @ load byte into r3        sub r3, #'0'              @ convert letter to digit        and r5, r2, #1            @ test if index is even or odd        cmp r5, #0        beq .odd_digit        bne .even_digit        .odd_digit:            add r6, r3              @ add digit to sum if odd            b .continue             @ skip next step        .even_digit:            lsl r3, #1              @ multiply digit by 2            cmp r3, #10             @ sum digits            subge r3, #10           @ get digit in 1s place            addge r3, #1            @ add 1 for the 10s place            add r7, r3              @ add digit sum to the total         .continue:         add r2, #1                @ increment digit index        cmp r2, r4                @ check if at end of string        blt .loadNext     add r0, r6, r7                @ add even and odd sum    mov r3, r0                    @ copy sum to r3    ldr r1, =429496730            @ (2^32-1)/10    sub r0, r0, r0, lsr #30       @ divide by 10    umull r2, r0, r1, r0    mov r1, #10    mul r0, r1                    @ multiply the r0 by 10 to see if divisible    cmp r0, r3                    @ compare with the original value in r3    .luhn_test_end:    movne r0, #0                  @ return false if invalid card number    moveq r0, #1                  @ return true if valid card number    pop {r1-r7, lr}    mov pc, lr length:    push {r1-r2, lr}    mov r2, r0              @ start of string address    .loop:        ldrb r1, [r2], #1   @ load byte from address r2 and increment        cmp r1, #0          @ check for end of string        bne .loop           @ load next byte if not 0    sub r0, r2, r0          @ subtract end of string address from start    sub r0, #1              @ end of line from count    pop {r1-r2, lr}    mov pc, lr @ reverses a string@ r0 address of string to reverse@ r1 address to store reversed stringreverse:    push {r0-r5, lr}    push {r0, lr}    bl length                @ get length of string to reverse    mov r3, r0               @ backword index    pop {r0, lr}    mov r4, #0               @ fowrard index    .reverse_next:        sub r3, #1           @ decrement backword index        ldrb r5, [r0, r3]    @ load byte from original string at index        strb r5, [r1, r4]    @ copy byte to reversed string        add r4, #1           @ increment fowrard index        cmp r3, #0           @ check if any characters are left        bge .reverse_next     mov r5, #0    strb r5, [r1, r4]  @ write null byte to terminate reversed string    pop {r0-r5, lr}    mov pc, lr isNumerical:    push {r1, lr}    .isNumerical_checkNext:        ldrb r1, [r0], #1        cmp r1, #0        beq .isNumerical_true        cmp r1, #'0'        blt .isNumerical_false        cmp r1, #'9'        bgt .isNumerical_false        b .isNumerical_checkNext    .isNumerical_false:        mov r0, #0        b .isNumerical_end    .isNumerical_true:        mov r0, #1    .isNumerical_end:    pop {r1, lr}    mov pc, lr  .datavalid_message:    .asciz " valid card number\n"invalid_message:    .asciz " invalid card number\n" reversed_string:    .space 32 example_numbers:    .asciz "49927398716"    .asciz "49927398717"    .asciz "1234567812345678"    .asciz "1234567812345670"

## Arturo

digits: function [n][    res: new []    while -> n > 0 [        'res ++ n % 10        n: n / 10    ]    res] luhn?: function [n][    s1: new 0    s2: new 0    loop.with: 'i digits n 'd [        if? even? i -> 's1 + d        else [            'd * 2            if d > 9 -> 'd - 9            's2 + d        ]    ]    zero? (s1 + s2) % 10] print luhn? 49927398716print luhn? 49927398717print luhn? 1234567812345678print luhn? 1234567812345670
Output:
true
false
false
true

## AutoHotkey

; Originally submitted by Laszlo:; http://www.autohotkey.com/forum/post-229412.html#229412 MsgBox % LuhnTest(49927398716)MsgBox % LuhnTest(49927398717)MsgBox % LuhnTest(1234567812345678)MsgBox % LuhnTest(1234567812345670) Return ;----------------------------- LuhnTest(Number){  MultFactor := 2 - ( StrLen(Number) & 1 )  ,  Sum := 0  Loop, Parse, Number    Sum += ( ( 9 < ( Temp := MultFactor * A_LoopField ) ) ? Temp - 9 : Temp )  ,  MultFactor := 3 - MultFactor  Return !Mod(Sum,10)}

## AutoIt

 Global $avarray[4] = [49927398716, 49927398717, 1234567812345678, 1234567812345670]For$i = 0 To 3	checkLuhn($avarray[$i])Next Func checkLuhn($number)$sum = 0	$numDigits = StringSplit($number, "")	For $i =$numDigits[0] - 1 To 1 Step -2		$numDigits[$i] = $numDigits[$i] * 2		If $numDigits[$i] >= 10 Then $numDigits[$i] -= 9	Next	For $i = 1 To$numDigits[0]		$sum +=$numDigits[$i] Next If StringRight($sum, 1) = "0" Then		ConsoleWrite("Luhn-Check (" & $number & ") : True" & @CRLF) Return True Else ConsoleWrite("Luhn-Check (" &$number & ") : False" & @CRLF)		Return False	EndIfEndFunc   ;==>checkLuhn
Output:
Luhn-Check (49927398716) : True
Luhn-Check (49927398717) : False
Luhn-Check (1234567812345678) : False
Luhn-Check (1234567812345670) : True

## AWK

#!/usr/bin/awk -fBEGIN {    A[1] = 49927398716;    A[2] = 49927398717;    A[3] = 1234567812345678;    A[4] = 1234567812345670;    A[5] = "01234567897";    A[6] = "01234567890";    A[7] = "00000000000";    for (k in A) print "isLuhn("A[k]"): ",isLuhn(A[k]);	} function isLuhn(cardno) {    s = 0;    m = "0246813579";    n = length(cardno);    for (k = n; 0 < k; k -= 2) {	s += substr(cardno, k, 1);    }    for (k = n-1; 0 < k; k -= 2) {	s += substr(m, substr(cardno, k, 1)+1, 1);    }    return ((s%10)==0);	}
Output:
isLuhn(1234567812345670):  1
isLuhn(01234567897):  1
isLuhn(01234567890):  0
isLuhn(00000000000):  1
isLuhn(49927398716):  1
isLuhn(49927398717):  0
isLuhn(1234567812345678):  0

## Bash

#!/bin/bash function luhn_validate  # <numeric-string>{    num=$1 shift 1 len=${#num}    is_odd=1    sum=0    for((t = len - 1; t >= 0; --t)) {        digit=${num:$t:1}         if [[ $is_odd -eq 1 ]]; then sum=$(( sum + $digit )) else sum=$(( $sum + ($digit != 9 ? ( ( 2 * $digit ) % 9 ) : 9 ) )) fi is_odd=$(( ! $is_odd )) } # NOTE: returning exit status of 0 on success return$(( 0 != ( $sum % 10 ) ))} function print_result # <numeric-string>{ if luhn_validate "$1"; then        echo "$1 is valid" else echo "$1 is not valid"    fi} print_result "49927398716"print_result "49927398717"print_result "1234567812345678"print_result "1234567812345670"
Output:
49927398716 is valid
49927398717 is not valid
1234567812345678 is not valid
1234567812345670 is valid


## BASIC

dim card$(5)card$[1]="49927398716"card$[2]="49927398717"card$[3]="1234567812345678"card$[4]="1234567812345670" for test = 1 to 4 odd = True sum = 0 for n = length(card$[test]) to 1 step -1        num = int(mid(card$[test],n,1)) if odd then sum += num odd = False else num *= 2 if num <= 9 then sum += num else sum += int(left(string(num),1)) + int(right(string(num),1)) end if odd = True end if next if sum mod 10 = 0 then print card$[test], "True"    else        print card$[test], "False" end ifnext test ### QBasic Works with: QBasic version 1.1 Works with: QuickBasic version 4.5 CONST True = -1: False = NOT True DIM card$(5)card$(1) = "49927398716"card$(2) = "49927398717"card$(3) = "1234567812345678"card$(4) = "1234567812345670" FOR test = 1 TO 4    odd = True    sum = 0    FOR n = LEN(card$(test)) TO 1 STEP -1 num = VAL(MID$(card$(test), n, 1)) IF odd THEN sum = sum + num odd = False ELSE num = num * 2 IF num <= 9 THEN sum = sum + num ELSE sum = sum + VAL(LEFT$(STR$(num), 1)) + VAL(RIGHT$(STR$(num), 1)) END IF odd = True END IF NEXT IF sum MOD 10 = 0 THEN PRINT card$(test), "True"    ELSE       PRINT card$(test), "False" END IFNEXT test ### True BASIC LET true = -1LET false = 0 DIM card$(5)LET card$(1) = "49927398716"LET card$(2) = "49927398717"LET card$(3) = "1234567812345678"LET card$(4) = "1234567812345670" FOR test = 1 TO 4    LET odd = true    LET sum = 0    FOR n = LEN(card$(test)) TO 1 STEP -1 LET num = VAL((card$(test))[n:n+1-1])        IF odd<>0 THEN           LET sum = sum + num           LET odd = false        ELSE           LET num = num*2           IF num <= 9 THEN              LET sum = sum + num           ELSE              LET sum = sum + VAL((STR$(num))[1:1]) + VAL((STR$(num))[LEN(STR$(num))-1+1:maxnum]) END IF LET odd = true END IF NEXT n IF remainder(round(sum),10) = 0 THEN PRINT card$(test), "True" ELSE PRINT card$(test), "False"NEXT testEND ### Yabasic dim card$(5)card$(1)="49927398716"card$(2)="49927398717"card$(3)="1234567812345678"card$(4)="1234567812345670" for test = 1 to 4    odd = true    sum = 0    for n = len(card$(test)) to 1 step -1 num = val(mid$(card$(test),n,1)) if odd then sum = sum + num odd = false else num = num * 2 if num <= 9 then sum = sum + num else sum = sum + val(left$(str$(num),1)) + val(right$(str$(num),1)) fi odd = true fi next if mod(sum, 10) = 0 then print card$(test), chr$(9), "True" else print card$(test), chr$(9), "False" finext test ## Batch File This simple implementation does not reverse the numbers. Instead, it counts from right to left. @echo offsetlocal enabledelayedexpansion call :luhn 49927398716call :luhn 49927398717call :luhn 1234567812345678call :luhn 1234567812345670exit /b 0 :luhnset "input=%1"set "cnt=0"set "s1=0"set "s2=0":digit_loopset /a "cnt-=1"set /a "isOdd=(-%cnt%)%%2" if !isodd! equ 1 ( set /a "s1+=!input:~%cnt%,1!") else ( set /a "twice=!input:~%cnt%,1!*2" if !twice! geq 10 ( set /a "s2+=!twice:~0,1!+!twice:~1,1!" ) else ( set /a "s2+=!twice!" ))if "!input:~%cnt%!"=="!input!" ( set /a "sum=(!s1!+!s2!)%%10" if !sum! equ 0 (echo !input! is valid.) else (echo !input! is not valid.) goto :EOF)goto digit_loop Output: >luhn.bat 49927398716 is valid. 49927398717 is not valid. 1234567812345678 is not valid. 1234567812345670 is valid. > ## BBC BASIC  FOR card% = 1 TO 4 READ cardnumber$        IF FNluhn(cardnumber$) THEN PRINT "Card number " cardnumber$ " is valid"        ELSE          PRINT "Card number " cardnumber$" is invalid" ENDIF NEXT card% END DATA 49927398716, 49927398717, 1234567812345678, 1234567812345670 DEF FNluhn(card$)      LOCAL I%, L%, N%, S%      L% = LEN(card$) FOR I% = 1 TO L% N% = VAL(MID$(card$, L%-I%+1, 1)) IF I% AND 1 THEN S% += N% ELSE N% *= 2 S% += N% MOD 10 + N% DIV 10 ENDIF NEXT = (S% MOD 10) = 0 ## bc /* Return 1 if number passes Luhn test, else 0 */define l(n) { auto m, o, s, x o = scale scale = 0 m = 1 while (n > 0) { x = (n % 10) * m if (x > 9) x -= 9 s += x m = 3 - m n /= 10 } s %= 10 scale = o if (s) return(0) return(1)} l(49927398716)l(49927398717)l(1234567812345678)l(1234567812345670) Output: 1 0 0 1 ## BCPL get "libhdr" let luhn(s) = valof$(  let sum=0 and fac=1    for i = s%0 to 1 by -1    $( unless '0' <= s%i <= '9' resultis false sum := sum + fac*(s%i - '0') rem 10 + fac*(s%i - '0')/10 fac := 3 - fac$)    resultis sum rem 10 = 0$) let show(s) be writef("%S: %S*N", s, luhn(s) -> "pass", "fail") let start() be$(  show("49927398716")    show("49927398717")    show("1234567812345678")    show("1234567812345670")$) Output: 49927398716: pass 49927398717: fail 1234567812345678: fail 1234567812345670: pass ## Befunge v 1 >$0 v   v                                    <>&:19+|v  <            >v      5      6   7      8^  \   <>09p19p>09g+09p:|>2*:19+%19g+19p19+/19g+19p:|   2          3      4  >                           v                              v"invalid"<10  9                                        |%+91+g91g90<                              v  "valid"<                              >:#,[email protected]                                 11 

The labelled points (1 to 11) are: 1. Read in input until number greater than 10, 2. Reverse the order, 3. Set accumulators to 0, 4. Add odd number to accumulator, 5. Mod even number with 10, 6. Add this digit to accumulator, 7. Integer divide number by 10, 8. Add this digit to accumulator, 9. Add odd and even accumulators, 10. Mod this accumulator with 10, 11. Print result.

The code requires input be separated by spaces and ended with a number greater than 10 to exit the reading loop. This could be done by reading characters and ending at a new line, but this way is much simpler.

Inputs:

4 9 9 2 7 3 9 8 7 1 6 99
4 9 9 2 7 3 9 8 7 1 7 99
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 99
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 0 99

Output:
valid
invalid
invalid
valid


## BQN

Luhn ← (0=10|⊢)∘(+´(10|⊢)+⊢≥10˙)∘(⊢×≠⥊1‿2˙)∘(⌽•Fmt-'0'˙) (⍉⊢≍Luhn¨) ⟨49927398716,49927398717,1234567812345678,1234567812345670⟩
Output:
┌─
╵      49927398716 1
49927398717 0
1234567812345678 0
1234567812345670 1
┘

## Bracmat

  ( luhn  =   sum odd even    .   0:?sum      & rev$!arg:?arg & whl ' ( @( !arg : %?odd ( %?even ?arg | :?arg&0:?even ) ) & !odd+mod$(2*!even.10)+div$(!even.5)+!sum:?sum ) & mod$(!sum.10):0  )& ( test  =       .   out      $(!arg ":" (luhn$!arg&true|false))  )& test$49927398716& test$49927398717& test$1234567812345678& test$1234567812345670& ;
Output:
49927398716 : true
49927398717 : false
1234567812345678 : false
1234567812345670 : true

## Brainf***

>>>>>>>>>+>,----------[                        READ CHARACTERS UNTIL \N AND  >++++++++[<----->-]<++>>>>>>+>,----------]   SUBTRACT ASCII 0 FROM EACH<-<<<<<<<                                      GO TO LAST DIGIT[                                              WHILE THERE ARE DIGITS  >>>>>>>>[-<<<<<<<+>>>>>>>]<<<<<<<<             ADD RUNNING TOTAL TO ODD DGT  <<<<<<<                                        GO TO EVEN DIGIT  [                                              IF THERE IS ONE    >[->++<]>[-<+>]                                MUL BY TWO    >>>++++++++++<<<<[                             DIVMOD BY TEN      >>>[-]+>-[<-<]<[<<]                            DECR DIVISOR      >>[                                            IF ZERO        >++++++++++>+<<-]<<<                           SET TO TEN; INCR QUOTIENT    -]                                               DECR DIVIDEND UNTIL ZERO    ++++++++++>>>>[-<<<<->>>>]                     CALCULATE REMAINDER    >[-<<<<<+>>>>>]                                ADD QUOTIENT TO IT    >>[-<<<<<<<+>>>>>>>]<<<<<<<<                   THEN ADD RUNNING TOTAL    <<<<<                                          ZERO BEFORE NEXT ODD DIGIT  ]<<                                            GO TO NEXT ODD DIGIT]>>>>>>>-[+>>-]>                                GO TO TOTAL>>>>++++++++++<<<<[                            MODULO TEN  >>>[-]+>-[<-<]<[<<]                            DECR DIVISOR  >>[>++++++++++<-]                              IF ZERO SET BACK TO TEN<<<-]                                            DECR DIVIDEND UNTIL ZERO>>>++++++++++>[-<->]<                          REMAINDER: TEN MINUS DIVISOR<<<<<<++++++++++[->                            VALUES FOR ASCII OUTPUT  +++++++++++>                                   110  ++++++++++>                                    100  ++++++++>                                      80  +++++++<<<<]                                   70>>>>>+>                                        GO BACK TO REMAINDER[<<.<<---.<-----.+++.<]                        IF NOT ZERO FAIL<[<<.<---.<+++++..<]                           IF ZERO PASS++++++++++.                                    NEWLINE 
Output:
$echo 49927398716 | beef luhn.bf Pass$ echo 49927398717 | beef luhn.bf
Fail
$echo 1234567812345678 | beef luhn.bf Fail$ echo 1234567812345670 | beef luhn.bf
Pass

## Burlesque

 tt         "Remove whitespace"vvpe         "Eval to number"vv<-         "Reverse digits"vvXX         "Split number into digits"vv { { "Odd digits"vv  2EN }   { "Even digits"vv  2en  {   2.*     "Double"vv   ^^ 9.>  "<test>=Duplicate greater than 9"vv   {    XX++   "Sum digits"vv   }if     "If <test>"vv  }m[      "For each even digit"vv }}M-       "Cool map. Create array of each branch applied to argument."vv {++}m[    "Sum each block (odd & even)"vv++        "Sum these"vv[-        "Last digit"vv0==       "Equal to zero"vvQ         "Pretty print"vv 
Output:
     49927398716        1
49927398717        0
1234567812345678        0
1234567812345670        1


## C

#include <string.h>#include <stdio.h> int luhn(const char* cc){	const int m[] = {0,2,4,6,8,1,3,5,7,9}; // mapping for rule 3	int i, odd = 1, sum = 0; 	for (i = strlen(cc); i--; odd = !odd) {		int digit = cc[i] - '0';		sum += odd ? digit : m[digit];	} 	return sum % 10 == 0;} int main(){	const char* cc[] = {		"49927398716",		"49927398717",		"1234567812345678",		"1234567812345670",		0	};	int i; 	for (i = 0; cc[i]; i++)		printf("%16s\t%s\n", cc[i], luhn(cc[i]) ? "ok" : "not ok"); 	return 0;}
Output:
     49927398716        ok
49927398717        not ok
1234567812345678        not ok
1234567812345670        ok


## C#

The LuhnCheck method takes an array of integers because values in memory will be integer-aligned.

     public static class Luhn    {        public static bool LuhnCheck(this string cardNumber)        {            return LuhnCheck(cardNumber.Select(c => c - '0').ToArray());        }         private static bool LuhnCheck(this int[] digits)        {            return GetCheckValue(digits) == 0;        }         private static int GetCheckValue(int[] digits)        {            return digits.Select((d, i) => i % 2 == digits.Length % 2 ? ((2 * d) % 10) + d / 5 : d).Sum() % 10;        }    }     public static class TestProgram    {        public static void Main()        {            long[] testNumbers = {49927398716, 49927398717, 1234567812345678, 1234567812345670};            foreach (var testNumber in testNumbers)                Console.WriteLine("{0} is {1}valid", testNumber, testNumber.ToString().LuhnCheck() ? "" : "not ");        }    } 
49927398716 is valid
49927398717 is not valid
1234567812345678 is not valid
1234567812345670 is valid


Note that the original implementation, which follows, is flawed because it assumes that n is a number which, when represented as a string, has an even number of characters. Granted, the brief is for Credit Card Numbers which are all, at the time of writing, an even number of digits.

using System;using System.Linq; namespace Luhn{    class Program    {        public static bool luhn(long n)        {            long nextdigit, sum = 0;                        bool alt = false;                        while (n != 0)            {                                nextdigit = n % 10;                if (alt)                {                    nextdigit *= 2;                    nextdigit -= (nextdigit > 9) ? 9 : 0;                }                sum += nextdigit;                alt = !alt;                n /= 10;            }            return (sum % 10 == 0);        }         public static bool luhnLinq(long n)        {            string s = n.ToString();            return s.Select((c, i) => (c - '0') << ((s.Length - i - 1) & 1)).Sum(n => n > 9 ? n - 9 : n) % 10 == 0;        }         static void Main(string[] args)        {                        long[] given = new long[] {49927398716, 49927398717, 1234567812345678, 1234567812345670};            foreach (long num in given)            {                string valid = (luhn(num)) ? " is valid" : " is not valid";                Console.WriteLine(num + valid);            }         }    }}
49927398716 is valid
49927398717 is not valid
1234567812345678 is not valid
1234567812345670 is valid


A solution without using LINQ, works for all versions of .NET.

 using System;namespace Luhn_Test{	public static class Extensions 	{		public static string Reverse(this string s )		{		    char[] charArray = s.ToCharArray();		    Array.Reverse( charArray );		    return new string( charArray );		}	}	class Program	{		public static bool Luhn(long x)		{			long s1=0;			long s2=0;			bool STATE=x%10!=0; // If it ends with zero, we want the order to be the other way around			x=long.Parse(x.ToString().Reverse());			while (x!=0)			{				s1+=STATE?x%10:0;				s2+=STATE?0:((x%10)*2>9)?(((x%10)*2/10)+((x%10)*2)%10):((x%10)*2); 				STATE=!STATE; //Switch state				x/=10; //Cut the last digit and continue			}			return ((s1+s2)%10==0); //Check if it ends with zero, if so, return true, otherwise,false.		}		public static void Main(string[] args)		{			long[] ks = {1234567812345670, 49927398717, 1234567812345678 ,1234567812345670 };			foreach (long k in ks)			{			Console.WriteLine("{0} is {1} Valid.",k,Luhn(k)?"":"Not");				}		Start:			try { 			Console.WriteLine("Enter your credit:");			long x=long.Parse(Console.ReadLine());			Console.WriteLine("{0} Valid.",Luhn(x)?"":"Not");			goto Start;			}			catch (FormatException)			{				goto Start;			}					}	}} 
1234567812345670 is Valid.
49927398717 is Not Valid.
1234567812345678 is Not Valid.
49927398716 is Valid.


 using System;using System.Linq; public class CreditCardLogic{    static Func<char, int> charToInt = c => c - '0';     static Func<int, int> doubleDigit = n => (n * 2).ToString().Select(charToInt).Sum();     static Func<int, bool> isOddIndex = index => index % 2 == 0;     public static bool LuhnCheck(string creditCardNumber)    {        var checkSum = creditCardNumber            .Select(charToInt)            .Reverse()            .Select((digit, index) => isOddIndex(index) ? digit : doubleDigit(digit))            .Sum();         return checkSum % 10 == 0;    }} 

Extremely compact version uses Europa rtl library https://github.com/CodeAlkemist/Europa-rtl

 using System;using EuropaRTL.Utilities; public static partial class Algoritmhs{    public static bool CheckLuhn(long n)    {        int s1 = n.Shatter(true).Subset(2).Arithmetic('+');        int s2 = n.Shatter(true).Subset(1, -1, 2).ArithmeticRA('*', 2).ShatterAndSum().Arithmetic('+');        return (s1 + s2) % 10 == 0 ? true : false;    }}class Program{    static void Main(string[] args)    {        long[] ll = {                49927398716,                49927398717,                1234567812345678,                1234567812345670            };        foreach (var item in ll)        {            item.ToString().WriteLine();            Algoritmhs.CheckLuhn(item).ToString().WriteLine();        }        Console.ReadKey();    }} 
49927398716
True
49927398717
False
1234567812345678
False
1234567812345670
False


## C++

#include <iostream>using namespace std; int toInt(const char c){    return c-'0';} int confirm( const char *id){    bool is_odd_dgt = true;    int s = 0;    const char *cp;     for(cp=id; *cp; cp++);    while(cp > id) {        --cp;        int k = toInt(*cp);        if (is_odd_dgt) {            s += k;        }        else {            s += (k!=9)? (2*k)%9 : 9;        }	is_odd_dgt = !is_odd_dgt;    }    return 0 == s%10;} int main( ){    const char * t_cases[] = {        "49927398716",        "49927398717",        "1234567812345678",        "1234567812345670",        NULL,    };    for ( const char **cp = t_cases; *cp; cp++) {        cout << *cp << ": " << confirm(*cp) << endl;    }    return 0;}

### C++11

#include <iostream>#include <vector>#include <algorithm>using namespace std; bool luhn( const string& id){  static const int m[10]  = {0,2,4,6,8,1,3,5,7,9}; // mapping for rule 3  bool is_odd_dgt = false;  auto lambda = [&](int a, char c) {return a + ((is_odd_dgt = !is_odd_dgt) ? c-'0' : m[c-'0']);};  int s = std::accumulate(id.rbegin(), id.rend(), 0, lambda);  return 0 == s%10;} int main( ){  auto t_cases = {"49927398716", "49927398717", "1234567812345678", "1234567812345670"};  auto print = [](const string & s) {cout << s << ": " << luhn(s) << endl;};  for_each(t_cases.begin(), t_cases.end(), print);  return 0;} 

It is also possible to achieve a compile-time version using metaprogramming.

#include <iostream>#include <type_traits> template<size_t I, int... Args>struct find_impl; template<int A, int... Args>struct find_impl<0, A, Args...> {    using type = std::integral_constant<int, A>;}; template<int A, int B, int... Args>struct find_impl<0, A, B, Args...> {    using type = std::integral_constant<int, A>;}; template<size_t I, int A, int B, int... Args>struct find_impl<I, A, B, Args...> {    using type = typename find_impl<I-1, B, Args...>::type;}; namespace detail {template<typename, typename>struct append_sequence{}; template<typename T, typename... Ts>struct append_sequence<T, std::tuple<Ts...>> {    using type = std::tuple<Ts..., T>;}; template<typename... Ts>struct reverse_sequence {    using type = std::tuple<>;}; template<typename T, typename... Ts>struct reverse_sequence<T, Ts...> {    using type = typename append_sequence<                            T,                            typename reverse_sequence<Ts...>::type                        >::type;};} template<size_t I>using rule3 = typename find_impl<I, 0, 2, 4, 6, 8, 1, 3, 5, 7, 9>::type; template<int A, char C, bool dgt>struct calc    : std::integral_constant<int, A + C - '0'>{}; template<int A, char C>struct calc<A, C, false>    : std::integral_constant<int, A + rule3<C - '0'>::type::value>{}; template<typename Acc, bool Dgt, char...>struct luhn_impl; template<typename Acc, bool Dgt, char A, char... Args>struct luhn_impl<Acc, Dgt, A, Args...> {    using type = typename calc<Acc::value, A, Dgt>::type;}; template<typename Acc, bool Dgt, char A, char B, char... Args>struct luhn_impl<Acc, Dgt, A, B, Args...> {    using type =        typename luhn_impl<typename calc<Acc::value, A, Dgt>::type, !Dgt, B, Args...>::type;}; template<typename>struct luhn; template<typename... Args>struct luhn<std::tuple<Args...>> {    using type = typename luhn_impl<std::integral_constant<int, 0>, true, Args::value...>::type;    constexpr static bool result = (type::value % 10) == 0;}; template<char... Args>bool operator "" _luhn() {    return luhn<typename detail::reverse_sequence<std::integral_constant<char, Args>...>::type>::result;} int main() {    std::cout << std::boolalpha;    std::cout << 49927398716_luhn << std::endl;    std::cout << 49927398717_luhn << std::endl;    std::cout << 1234567812345678_luhn << std::endl;    std::cout << 1234567812345670_luhn << std::endl;    return 0;} 
true
false
false
true


## Caché ObjectScript

Class Utils.Check [ Abstract ]{ ClassMethod Luhn(x As %String) As %Boolean{	// https://www.simple-talk.com/sql/t-sql-programming/calculating-and-verifying-check-digits-in-t-sql/	SET x=$TRANSLATE(x," "), cd=$EXTRACT(x,*)	SET x=$REVERSE($EXTRACT(x,1,*-1)), t=0	FOR i=1:1:$LENGTH(x) { SET n=$EXTRACT(x,i)		IF i#2 SET n=n*2 IF $LENGTH(n)>1 SET n=$EXTRACT(n,1)+$EXTRACT(n,2) SET t=t+n } QUIT cd=((t*9)#10)} } Examples: USER>For { Read ccn Quit:ccn="" Write ": "_##class(Utils.Check).Luhn(ccn), ! } 49927398716: 1 49927398717: 0 1234567812345678: 0 1234567812345670: 1 USER> ## Ceylon shared void run() { value numbers = "49927398716 49927398717 1234567812345678 1234567812345670"; for(number in numbers.lines) { print("number passes? luhn(number)"); }} shared Boolean luhn(String number) { value digits = number .reversed .map(Character.string) .map(Integer.parse) .narrow<Integer>(); value s1 = sum { 0, *digits.by(2) }; value s2 = sum { 0, *digits .skip(1) .by(2) .map(curry(times<Integer>)(2)) .map((Integer element) => element / 10 + element % 10) }; return (s1 + s2) % 10 == 0;} ## Clojure (defn luhn? [cc] (let [factors (cycle [1 2]) numbers (map #(Character/digit % 10) cc) sum (reduce + (map #(+ (quot % 10) (mod % 10)) (map * (reverse numbers) factors)))] (zero? (mod sum 10)))) (doseq [n ["49927398716" "49927398717" "1234567812345678" "1234567812345670"]] (println (luhn? n))) ## CLU luhn = proc (num: string) returns (bool) signals (bad_format) total: int := 0 even: bool := true for i: int in int$from_to_by(string$size(num), 1, -1) do digit: int := int$parse(string$c2s(num[i])) resignal bad_format even := ~even if even then digit := 2 * digit if digit >= 10 then digit := digit//10 + 1 end end total := total + digit end return(total // 10 = 0)end luhn start_up = proc () po: stream := stream$primary_output()    tests: sequence[string] := sequence[string]$["49927398716", "49927398717", "1234567812345678", "1234567812345670"] for test: string in sequence[string]$elements(tests) do        stream$puts(po, test || ": ") if luhn(test) then stream$putl(po, "pass")            else stream$putl(po, "fail") end endend start_up Output: 49927398716: pass 49927398717: fail 1234567812345678: fail 1234567812345670: pass ## COBOL Works with: OpenCOBOL  IDENTIFICATION DIVISION. PROGRAM-ID. LUHNTEST. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. data division. WORKING-STORAGE SECTION. 01 inp-card. 03 inp-card-ch pic x(01) occurs 20 times. 01 ws-result pic 9(01). 88 pass-luhn-test value 0. PROCEDURE DIVISION. move "49927398716" to inp-card perform test-card move "49927398717" to inp-card perform test-card move "1234567812345678" to inp-card perform test-card move "1234567812345670" to inp-card perform test-card stop run . test-card. call "LUHN" using inp-card, ws-result if pass-luhn-test display "input=" inp-card "pass" else display "input=" inp-card "fail" . END PROGRAM LUHNTEST. IDENTIFICATION DIVISION. PROGRAM-ID. LUHN. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. DATA DIVISION. WORKING-STORAGE SECTION. 01 maxlen pic 9(02) comp value 16. 01 inplen pic 9(02) comp value 0. 01 i pic 9(02) comp value 0. 01 j pic 9(02) comp value 0. 01 l pic 9(02) comp value 0. 01 dw pic 9(02) comp value 0. 01 ws-total pic 9(03) comp value 0. 01 ws-prod pic 99. 01 filler redefines ws-prod. 03 ws-prod-tens pic 9. 03 ws-prod-units pic 9. 01 ws-card. 03 filler occurs 16 times depending on maxlen. 05 ws-card-ch pic x(01). 05 ws-card-digit redefines ws-card-ch pic 9(01). LINKAGE SECTION. 01 inp-card. 03 inp-card-ch pic x(01) occurs 20 times. 01 ws-result pic 9(01). 88 pass-luhn-test value 0. PROCEDURE DIVISION using inp-card, ws-result. perform varying i from 1 by +1 until i > maxlen or inp-card-ch (i) = space end-perform compute l = i - 1 compute inplen = l perform varying j from 1 by +1 until j > inplen if l < 1 move "0" to ws-card-ch (j) else move inp-card-ch (l) to ws-card-ch (j) compute l = l - 1 end-if end-perform move 0 to ws-total perform varying i from 1 by +1 until i > inplen compute dw = 2 - (i - 2 * function integer (i / 2)) compute ws-prod = ws-card-digit (i) * dw compute ws-total = ws-total + ws-prod-tens + ws-prod-units end-perform compute ws-result = ws-total - 10 * function integer (ws-total / 10) goback . END PROGRAM LUHN. Output: input=49927398716 pass input=49927398717 fail input=1234567812345678 fail input=1234567812345670 pass  ## Comal 0010 FUNC luhn(s$) CLOSED0020   total#:=00030   even#:=TRUE0040   FOR i#:=LEN(s$) TO 1 STEP -1 DO0050 digit#:=VAL(s$(i#))0060     even#:=NOT even#0070     IF even# THEN digit#:=(2*digit#) DIV 10+(2*digit#) MOD 100080     total#:+digit#0090   ENDFOR i#0100   RETURN total# MOD 10=00110 ENDFUNC luhn0120 //0130 PROC test(s$)0140 PRINT s$,": ",0150   IF luhn(s$) THEN0160 PRINT "pass"0170 ELSE0180 PRINT "fail"0190 ENDIF0200 ENDPROC test0210 //0220 test("49927398716")0230 test("49927398717")0240 test("1234567812345678")0250 test("1234567812345670")0260 END Output: 49927398716: pass 49927398717: fail 1234567812345678: fail 1234567812345670: pass ## Common Lisp (defun luhn (n) (labels ((sum-digits (n) (if (> n 9) (- n 9) n))) (let ((n* (reverse n)) (l (length n))) (let ((s1 (loop for i from 0 below l by 2 summing (digit-char-p (aref n* i)))) (s2 (loop for i from 1 below l by 2 summing (sum-digits (* 2 (digit-char-p (aref n* i))))))) (zerop (mod (+ s1 s2) 10)))))) Another version, using Maciej Pasternacki's reader macros for function composition and currying in the curly package: (require :curly)(use-package :curly)(enable-curly-syntax) (defun luhn (seq) (labels ((sum-digits (n) (if (> n 9) (- n 9) n))) (funcall {zerop (mod * 10) (apply #'+) (mapcar #'sum-digits) (mapcar #'* '#1=(1 2 . #1#)) (map 'list #'digit-char-p) reverse} seq))) ## Cowgol include "cowgol.coh"; # Given a string containing the digits of a credit card number,# see if it passes the Luhn test.sub luhn(card: [uint8]): (ok: uint8) is # Scan ahead to last digit, counting digits var n: uint8 := 0; while [card] != 0 loop n := n + 1; card := @next card; end loop; var sum: uint8 := 0; while n > 0 loop # odd digit is simply added card := @prev card; n := n - 1; sum := sum + ([card] - '0'); # if uneven amount of digits, stop if n == 0 then break; end if; # even digit card := @prev card; n := n - 1; var digit := [card] - '0'; # it is good to avoid unnecessary multiplication/ # division, since 8-bit processors and microcontrollers # don't tend to have that in hardware if digit < 5 then sum := sum + digit + digit; else digit := digit - 5; sum := sum + digit + digit + 1; end if; end loop; # there is no boolean type, comparisons only work # in conditionals; this is the only way to return # a status if sum % 10 == 0 then ok := 1; else ok := 0; end if;end sub; # Test and printsub test(card: [uint8]) is var msg: [uint8][] := {"Fail", "Pass"}; print(card); print(": "); print(msg[luhn(card)]); print_nl();end sub; test("49927398716");test("49927398717");test("1234567812345678");test("1234567812345670"); Output: 49927398716: Pass 49927398717: Fail 1234567812345678: Fail 1234567812345670: Pass ## Crystal def luhn_valid?(n) # Card values can be numbers or strings d2sum = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9] sum, n = 0, n.to_u64 while n > 0; sum += n%10; n //= 10; sum += d2sum[n%10]; n //= 10 end sum % 10 == 0end cards = [49927398716, "49927398717", 1234567812345678, "1234567812345670"]cards.each{ |i| puts "#{i}: #{luhn_valid?(i)}" } Output: 49927398716: true 49927398717: false 1234567812345678: false 1234567812345670: true ## D ### Functional Version Translation of: Haskell import std.algorithm, std.range, std.string; enum luhnTest = (in string n) pure /*nothrow*/ @safe /*@nogc*/ => retro(n) .zip(only(1, 2).cycle) .map!(p => (p[0] - '0') * p[1]) .map!(d => d / 10 + d % 10) .sum % 10 == 0; void main() { assert("49927398716 49927398717 1234567812345678 1234567812345670" .split.map!luhnTest.equal([true, false, false, true]));} ### More Imperative Version Translation of: C import std.algorithm; bool luhnTest(in string num) @safe pure nothrow @nogc { uint sum; foreach_reverse (immutable i, immutable n; num) { immutable uint ord = n - '\u0030'; sum += ((num.length - i) & 1) ? ord : ord / 5 + (2 * ord) % 10; } return sum % 10 == 0;} void main() { immutable data = ["49927398716", "49927398717", "1234567812345678", "1234567812345670"]; assert(data.map!luhnTest.equal([true, false, false, true]));} ### Stronger Statically Typed Version This version uses more precise types. Translation of: SPARK import std.stdio; struct Interval(T) { immutable T a, b; this(in T a_, in T b_) pure nothrow @nogc { this.a = a_; this.b = b_; } bool opBinaryRight(string op="in")(in T x) const pure nothrow @nogc { return x >= a && x <= b; } pure nothrow @safe @nogc const invariant { assert(a <= b); }} Interval!T interval(T)(in T a, in T b) pure nothrow @nogc { return Interval!T(a, b);} bool luhnTest(in string num) pure nothrow @nogcin { assert(num.length <= 20);} body { int sum = 0; bool od = true; bool ok = true; immutable int numLen = num.length; foreach_reverse (immutable p; 0 .. numLen) { immutable int i = num[p] - '0'; if (i !in interval(0, 9)) { ok = false; break; } immutable int x = ((i * 2) % 10) + (i / 5); assert((numLen - p) in interval(0, 19)); assert(sum in interval(0, (numLen - p) * 10)); assert(i in interval(0, 9)); assert(x in interval(0, 9)); sum += od ? i : x; od = !od; } return ok && (sum % 10) == 0;} void main() { foreach (immutable n; ["49927398716", "49927398717", "1234567812345678", "1234567812345670", "123456781234567D"]) writefln("%s is %svalid", n, luhnTest(n) ? "" : "not ");} ## Draco proc nonrec luhn(*char num) bool: [10] byte map = (0, 2, 4, 6, 8, 1, 3, 5, 7, 9); byte total, digit; *char start; bool even; start := num; total := 0; even := true; while num* /= '\e' do num := num + 1 od; while num := num - 1; num >= start do digit := num* - '0'; even := not even; if even then digit := map[digit] fi; total := total + digit od; total % 10 = 0corp proc nonrec test(*char num) void: writeln(num, ": ", if luhn(num) then "pass" else "fail" fi)corp proc nonrec main() void: test("49927398716"); test("49927398717"); test("1234567812345678"); test("1234567812345670")corp Output: 49927398716: pass 49927398717: fail 1234567812345678: fail 1234567812345670: pass ## EchoLisp  ;; value for 'even' numbers(define (even-val n) (if (> n 4) (+ n n -9) (+ n n))) ;;Luhn test;; input : a string of decimal digits;; output #t or #f(define (valid nums (odd #f )) (let ((nums (map string->number (reverse (string->list nums))))) (= 0 (modulo (for/sum ((n nums)) (set! odd (not odd)) (if odd n (even-val n))) 10)))) (valid "49927398716") → #t(valid "1234567812345670") → #t(valid "1234567812345678") → #f(valid "49927398717") → #f  ## Elixir defmodule Luhn do def valid?(cc) when is_binary(cc), do: String.to_integer(cc) |> valid? def valid?(cc) when is_integer(cc) do 0 == Integer.digits(cc) |> Enum.reverse |> Enum.chunk(2, 2, [0]) |> Enum.reduce(0, fn([odd, even], sum) -> Enum.sum([sum, odd | Integer.digits(even*2)]) end) |> rem(10) endend numbers = ~w(49927398716 49927398717 1234567812345678 1234567812345670)for n <- numbers, do: IO.puts "#{n}: #{Luhn.valid?(n)}" Output: 49927398716: true 49927398717: false 1234567812345678: false 1234567812345670: true  ## Emacs Lisp Library: seq.el (require 'seq) (defun luhn (str) "Check if STR is a valid credit card number using the Luhn algorithm." (if (string-match-p "[^0-9]" str) (error "String contains invalid character") (let ((digit-list (reverse (mapcar #'(lambda (x) (- x 48)) (string-to-list str))))) (zerop (mod (apply #'+ (seq-map-indexed (lambda (elt idx) (if (not (zerop (% idx 2))) (if (> (* 2 elt) 9) (- (* 2 elt) 9) (* 2 elt)) elt)) digit-list)) 10))))) (mapcar #'luhn '("49927398716" "49927398717" "1234567812345678" "1234567812345670")) Output: (t nil nil t)  ## Erlang  -module(luhn_test). -export( [credit_card/1, task/0] ). luhn_sum([Odd, Even |Rest]) when Even >= 5 -> Odd + 2 * Even - 10 + 1 + luhn_sum(Rest);luhn_sum([Odd, Even |Rest]) -> Odd + 2 * Even + luhn_sum(Rest);luhn_sum([Odd]) -> Odd;luhn_sum([]) -> 0. check( Sum ) when (Sum rem 10) =:= 0 -> valid;check( _Sum ) -> invalid. credit_card(Digits) -> check(luhn_sum(lists:map(fun(D) -> D-$0 end, lists:reverse(Digits)))). task() ->    Numbers = ["49927398716", "49927398717", "1234567812345678", "1234567812345670"],    [io:fwrite("~s: ~p~n", [X, credit_card(X)]) || X <- Numbers]. 
Output:
16> luhn_test:task().
49927398716: valid
49927398717: invalid
1234567812345678: invalid
1234567812345670: valid


## Euphoria

Translation of: C
function luhn(sequence cc)    integer isOdd, oddSum, evenSum, digit    isOdd = 1    oddSum = 0    evenSum = 0    for i = length(cc) to 1 by -1 do        digit = cc[i] - '0'        if isOdd then            oddSum += digit        else            evenSum += floor(digit / 5) + remainder(2 * digit, 10)        end if        isOdd = not isOdd    end for    return not remainder(oddSum + evenSum, 10)end function constant cc_numbers = {    "49927398716",    "49927398717",    "1234567812345678",    "1234567812345670"} for i = 1 to length(cc_numbers) do    printf(1,"%s = %d\n", {cc_numbers[i], luhn(cc_numbers[i])})end for
Output:
49927398716 = 1
49927398717 = 0
1234567812345678 = 0
1234567812345670 = 1

## Excel

### LAMBDA

Binding the name luhnChecked to the following lambda expression in the Name Manager of the Excel WorkBook:

luhnChecked=LAMBDA(s,    LET(        ns, REVERSECOLS(VALUE(CHARSROW(s))),        ixs, SEQUENCE(1, COLUMNS(ns), 1, 1),         0 = MOD(SUM(                FILTER(ns, 0 <> MOD(ixs, 2))            ) + (                LAMBDA(n,                    DIGITSUM(                        CONCAT(TEXT(2 * n, "0"))                    )                )(                    FILTER(ns, 0 = MOD(ixs, 2))                )            ),            10        )    ))

and also assuming the following generic bindings in the Name Manager for the WorkBook:

CHARSROW=LAMBDA(s,    MID(s,        SEQUENCE(1, LEN(s), 1, 1),        1    ))  DIGITSUM=LAMBDA(s,    SUM(VALUE(        MID(s,            SEQUENCE(LEN(s), 1, 1, 1),            1        )    )))  REVERSECOLS=LAMBDA(xs,    LET(        n, COLUMNS(xs),         SORTBY(            xs,            SEQUENCE(1, n, n, -1)        )    ))
Output:
 =luhnChecked(A2) fx A B 1 Digit strings Luhn result 2 49927398716 TRUE 3 49927398717 FALSE 4 1234567812345678 FALSE 5 1234567812345670 TRUE

## F#

let luhn (s:string) =  let rec g r c = function  | 0 -> r  | i ->      let d = ((int s.[i - 1]) - 48) <<< c      g (r + if d < 10 then d else d - 9) (1 - c) (i - 1)  (g 0 0 s.Length) % 10 = 0

## Factor

Works with: Factor version 0.98
USING: kernel math math.parser math.order math.ranges sequences ;IN: luhn : reversed-digits ( n -- list )    { } swap    [ dup 0 > ]        [ 10 /mod  swapd suffix  swap ]    while drop ; : luhn-digit  ( n -- n )    reversed-digits dup length <iota> [        2dup swap nth        swap odd? [ 2 *  10 /mod + ] when    ] map sum 10 mod    nip ; : luhn? ( n -- ? )    luhn-digit 0 = ; 
Output:
( scratchpad ) 49927398716 luhn? .
t
( scratchpad ) 49927398717 luhn? .
f
( scratchpad ) 1234567812345678 luhn? .
f
( scratchpad ) 1234567812345670 luhn? .
t


## Forth

: luhn ( addr len -- ? )  0 >r over +             ( R: sum )  begin  1- 2dup <=  while                   \ odd         dup [email protected] [char] 0 -         r> + >r         1- 2dup <=  while                   \ even         dup [email protected] [char] 0 -         2* 10 /mod +     \ even digits doubled, split, and summed         r> + >r  repeat then  2drop  r> 10 mod 0= ; s" 49927398716"      luhn .   \ -1s" 49927398717"      luhn .   \ 0s" 1234567812345678" luhn .   \ 0s" 1234567812345670" luhn .   \ -1

## Fortran

program luhn  implicit none  integer              :: nargs  character(len=20)    :: arg  integer              :: alen, i, dr  integer, allocatable :: number(:)  integer, parameter   :: drmap(0:9) = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9]   ! Get number  nargs = command_argument_count()  if (nargs /= 1) then     stop  end if  call get_command_argument(1, arg, alen)  allocate(number(alen))  do i=1, alen     number(alen-i+1) = iachar(arg(i:i)) - iachar('0')  end do   ! Calculate number  dr = 0  do i=1, alen     dr = dr + merge(drmap(number(i)), number(i), mod(i,2) == 0)  end do   if (mod(dr,10) == 0) then     write(*,'(a,i0)') arg(1:alen)//' is valid'  else     write(*,'(a,i0)') arg(1:alen)//' is not valid'  end ifend program luhn ! Results:! 49927398716 is valid! 49927398717 is not valid! 1234567812345678 is not valid! 1234567812345670 is valid

## FreeBASIC

' version 05-07-2015' compile with: fbc -s console #Ifndef TRUE        ' define true and false for older freebasic versions    #Define FALSE 0    #Define TRUE Not FALSE#EndIf Function luhntest(cardnr As String) As Integer     cardnr = Trim(cardnr) ' we don't want spaces    Dim As String reverse_nr = cardnr    Dim As Integer i, j, s1, s2, l = Len(cardnr) - 1     ' reverse string    For i = 0 To l        reverse_nr[i] = cardnr[l - i]    Next    ' sum odd numbers    For i = 0 To l Step 2        s1 = s1 + (reverse_nr[i] - Asc("0"))    Next    ' sum even numbers    For i = 1 To l Step 2        j = reverse_nr[i] - Asc("0")        j = j * 2        If j > 9 Then j = j Mod 10 + 1        s2 = s2 + j    Next     If (s1 + s2) Mod 10 = 0 Then        Return TRUE    Else        Return FALSE    End If End Function ' ------=< MAIN >=------ Dim As String input_nr(1 To ...) = {"49927398716", "49927398717",_                          "1234567812345678", "1234567812345670"}Dim As Integer a Print  "Task test number 49927398716 should be TRUE, report back as ";Print IIf(luhntest("49927398716" ) = TRUE, "TRUE", "FALSE")Print : Print Print "test card nr:"For a = 1 To UBound(input_nr)    Print input_nr(a); " = "; IIf(luhntest(input_nr(a)) = TRUE, "TRUE", "FALSE")Next ' empty keyboard bufferWhile InKey <> "" : WendPrint : Print "hit any key to end program"SleepEnd
Output:
Task test number 49927398716 should be TRUE, report back as TRUE

test card nr:
49927398716 = TRUE
49927398717 = FALSE
1234567812345678 = FALSE
1234567812345670 = TRUE

## Free Pascal

program luhn;   function lunh(arg: string): boolean;  var    i, sum: integer;    temp: byte;  begin    sum := 0;    for i:= length(arg) downto 1 do begin  // Run the characters backwards      temp := byte(arg[i])-48;             // Convert from ASCII to byte      if (length(arg)-i) mod 2 = 0        then sum := sum + temp             // Odd characters just add        else if temp < 5           then sum := sum + 2*temp        // Even characters add double           else sum := sum + (2*temp)-9;   // or sum the digits of the doubling    end;    result := sum mod 10 = 0;              // Return true if sum ends in a 0  end; begin  writeln('     49927398716: ', lunh('49927398716'));  writeln('     49927398717: ', lunh('49927398717'));  writeln('1234567812345678: ', lunh('1234567812345678'));  writeln('1234567812345670: ', lunh('1234567812345670'));end.
Output:
     49927398716: TRUE
49927398717: FALSE
1234567812345678: FALSE
1234567812345670: TRUE

## FunL

def luhn_checksum( card_number ) =  def digits_of( n ) = [int(d) | d <- n.toString()]   digits = digits_of( card_number ).reverse()  odd_digits = digits(0:digits.length():2)  even_digits = digits(1:digits.length():2)  (sum( odd_digits ) + sum( sum(digits_of(d*2)) | d <- even_digits )) mod 10 def is_luhn_valid( card_number ) = luhn_checksum( card_number ) == 0 for n <- [49927398716, 49927398717, 1234567812345678, 1234567812345670]  println( n + ' is ' + (if is_luhn_valid(n) then 'valid' else 'invalid') )
Output:
49927398716 is valid
49927398717 is invalid
1234567812345678 is invalid
1234567812345670 is valid


## Gambas

Public Sub Main()Dim sTrial As String[] = ["49927398716", "49927398717", "1234567812345678", "1234567812345670"]Dim sRev As StringDim siCount, siOdd, siEven, siHold, siQty As Short For siQty = 0 To sTrial.Max   siOdd = 0  siEven = 0  sRev = ""   For siCount = Len(sTrial[siQty]) DownTo 1    sRev &= Mid(sTrial[siQty], siCount, 1)  Next   For siCount = 1 To Len(sRev)    If Odd(siCount) Then siOdd += Val(Mid(sRev, siCount, 1))    If Even(siCount) Then      siHold = Val(Mid(sRev, siCount, 1)) * 2      If siHold > 9 Then         siEven += Val(Mid(Str(siHold), 1, 1)) + Val(Mid(Str(siHold), 2, 1))      Else        siEven += Val(Mid(sRev, siCount, 1)) * 2      End If    End If  Next   sRev = Str(siOdd + siEven)  If sRev Ends "0" Then     Print sTrial[siQty] & " is a valid number"  Else    Print sTrial[siQty] & " is NOT a valid number"  End IfNext End

Output:

49927398716 is a valid number
49927398717 is NOT a valid number
1234567812345678 is NOT a valid number
1234567812345670 is a valid number


## GAP

IsLuhn := function(n)	local c, d, i, j, r;	d := "0123456789";	j := 1;	r := 0;	for c in Reversed(String(n)) do		i := Position(d, c);		if i = fail then			continue;		fi;		i := j*(i - 1);		r := r + QuoInt(i, 10) + RemInt(i, 10);		j := 3 - j;	od;	return RemInt(r, 10) = 0;end; List([49927398716, 49927398717, 1234567812345678, 1234567812345670], IsLuhn);# [ true, false, false, true ] # Will also work on strings, and will skip non-digitsIsLuhn("4-992-739-871-6");# true

## Go

package main import (    "fmt"    "strings") const input = 499273987164992739871712345678123456781234567812345670 var t = [...]int{0, 2, 4, 6, 8, 1, 3, 5, 7, 9} func luhn(s string) bool {    odd := len(s) & 1    var sum int    for i, c := range s {        if c < '0' || c > '9' {            return false        }        if i&1 == odd {            sum += t[c-'0']        } else {            sum += int(c - '0')        }    }    return sum%10 == 0} func main() {    for _, s := range strings.Split(input, "\n") {        fmt.Println(s, luhn(s))    }}
Output:
49927398716 true
49927398717 false
1234567812345678 false
1234567812345670 true


## Groovy

def checkLuhn(number) {    int total    (number as String).reverse().eachWithIndex { ch, index ->        def digit = Integer.parseInt(ch)        total += (index % 2 ==0) ? digit : [0, 2, 4, 6, 8, 1, 3, 5, 7, 9][digit]    }    total % 10 == 0}

Testing the function:

def verifyLuhn(number, expected) {    println "Checking: $number (${checkLuhn(number)})"    assert expected == checkLuhn(number)} [49927398716: true, 49927398717: false, 1234567812345678: false, 1234567812345670: true].each { number, expected ->    verifyLuhn number, expected}
Output:
Checking: 49927398716 (true)
Checking: 49927398717 (false)
Checking: 1234567812345678 (false)
Checking: 1234567812345670 (true)

import Data.Char (digitToInt)luhn = (0 ==) . (mod 10) . sum . map (uncurry (+) . (divMod 10)) .       zipWith (*) (cycle [1,2]) . map digitToInt . reverse
Output:
map luhn ["49927398716", "49927398717", "1234567812345678", "1234567812345670"][True,False,False,True]

Or, aiming for a legible relationship with the stages shown in the task description:

import Data.Char (digitToInt)import Data.List (transpose)import Data.List.Split (chunksOf) luhn :: String -> Boolluhn x = 0 == rem (s1 + s2) 10  where    stringInts = fmap digitToInt    [odds, evens] =      (transpose . chunksOf 2)        (stringInts $reverse x) s1 = sum odds s2 = sum$ sum . stringInts . show . (2 *) <$> evens main :: IO ()main = mapM_ (print . ((,) <*> luhn)) [ "49927398716", "49927398717", "1234567812345678", "1234567812345670" ] Output: ("49927398716",True) ("49927398717",False) ("1234567812345678",False) ("1234567812345670",True) ## HicEst CHARACTER numbers="49927398716 49927398717 1234567812345678 1234567812345670 " DO nr = 1, 4 EDIT(Text=numbers, ITeM=nr, Parse=number) sum_odds = 0 sum_even = 0 DO i = LEN(number), 1, -2 sum_odds = sum_odds + ICHAR(number(i)) - 48 IF(i > 1) THEN even2 = 2 * (ICHAR(number(i-1)) - 48) sum_even = sum_even + MOD(even2, 10) + INT(even2/10) ENDIF ENDDO valid = (0 == MOD(sum_odds + sum_even, 10)) WRITE() number, " is ", "invalid"(1 + 2*valid:)ENDDO 49927398716 is valid 49927398717 is invalid 1234567812345678 is invalid 1234567812345670 is valid ## Icon and Unicon We use map to pre-compute the sum of doubled digits. procedure main(aL)every write(i := !aL ," - ", ((\isluhn10(i),"valid")|"invalid") \ 1)end procedure isluhn10(i) #: isluhn10(i) returns i (if i passes luhn10) or fails local sum sum :=0reverse(integer(i)) ? while not pos(0) do { sum +:= move(1) sum +:= map(move(1),"0123456789","0246813579") } return (sum % 10 = 0,i)end Output: # luhn10 49927398716 49927398717 1234567812345678 1234567812345670 49927398716 - valid 49927398717 - invalid 1234567812345678 - invalid 1234567812345670 - valid  ## IS-BASIC 100 PROGRAM "CredCard.bas"110 DO120 PRINT :PRINT "Credit card number:":INPUT PROMPT ">":CCN$130   IF CCN$="" THEN EXIT DO140 IF LUHN(TRIM$(CCN$)) THEN150 PRINT "Card number is valid."160 ELSE170 SET #102:INK 3:PRINT "Card number is invalid.":SET #102:INK 1180 END IF190 LOOP200 DEF LUHN(CCN$)210   LET L=LEN(CCN$):LET S=0220 FOR I=1 TO L230 LET N=VAL(CCN$(L-I+1))240     IF I BAND 1 THEN250       LET S=S+N260     ELSE270       LET N=N*2:LET S=S+MOD(N,10)+INT(N/10)280     END IF290   NEXT300   LET LUHN=MOD(S,10)=0310 END DEF320 DEF TRIM$(S$)330   LET T$=""340 FOR I=1 TO LEN(S$)350     IF S$(I)>CHR$(47) AND S$(I)<CHR$(58) THEN LET T$=T$&S$(I)360 NEXT370 LET TRIM$=T$380 END DEF Output: Credit card number: >49927398716 Card number is valid. Credit card number: >49927398717 Card number is invalid. Credit card number: >1234 5678 1234 5678 Card number is invalid. Credit card number: >1234 5678 1234 5670 Card number is valid. ## J We can treat the odd digits the same as even digits, except that they are not doubled. Also, we do not need the intermediate sums. luhn=: 0 = 10 (| +/@,) 10 #.inv 1 2 *&|: _2 "."0\ |. Example use:  luhn&> '49927398716';'49927398717';'1234567812345678';'1234567812345670'1 0 0 1 Interpreting that example: In J, 1 is true, 0 is false, so the first and last provided digit sequences were valid and the middle two were not. ## Java public class Luhn { public static void main(String[] args) { System.out.println(luhnTest("49927398716")); System.out.println(luhnTest("49927398717")); System.out.println(luhnTest("1234567812345678")); System.out.println(luhnTest("1234567812345670")); } public static boolean luhnTest(String number){ int s1 = 0, s2 = 0; String reverse = new StringBuffer(number).reverse().toString(); for(int i = 0 ;i < reverse.length();i++){ int digit = Character.digit(reverse.charAt(i), 10); if(i % 2 == 0){//this is for odd digits, they are 1-indexed in the algorithm s1 += digit; }else{//add 2 * digit for 0-4, add 2 * digit - 9 for 5-9 s2 += 2 * digit; if(digit >= 5){ s2 -= 9; } } } return (s1 + s2) % 10 == 0; }} Output: true false false true ## JavaScript Using prototype. mod10check = function(cc) { return$A(cc).reverse().map(Number).inject(0, function(s, d, i) {    return s + (i % 2 == 1 ? (d == 9 ? 9 : (d * 2) % 9) : d);  }) % 10 == 0;};['49927398716','49927398717','1234567812345678','1234567812345670'].each(function(i){alert(mod10check(i))});

Without any library.

var LuhnCheck = (function(){	var luhnArr = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9];	return function(str)	{		var counter = 0;		var incNum;		var odd = false;		var temp = String(str).replace(/[^\d]/g, "");		if ( temp.length == 0)			return false;		for (var i = temp.length-1; i >= 0; --i)		{			incNum = parseInt(temp.charAt(i), 10);			counter += (odd = !odd)? incNum : luhnArr[incNum];		}		return (counter%10 == 0);	}})();

Highly compressed version.

var luhn10 = function(a,b,c,d,e) {  for(d = +a[b = a.length-1], e=0; b--;)    c = +a[b], d += ++e % 2 ? 2 * c % 10 + (c > 4) : c;  return !(d%10)}; // returns trueluhn10('4111111111111111')  // returns falseluhn10('4111111111111112')  

Naive implementation

const lunhCheck = (str) => {    const sumDigit = (c) => (c < 10) ? c :              sumDigit( Math.trunc(c / 10) + (c % 10));     return str.split('').reverse()              .map(Number)              .map((c, i) => i % 2 !== 0 ? sumDigit(c * 2) : c)              .reduce((acc,v) => acc + v) % 10 === 0;}; lunhCheck('49927398716'); // returns truelunhCheck('49927398717'); // returns falselunhCheck('1234567812345678'); // returns falselunhCheck('1234567812345670'); // returns true 

## jq

Works with: jq version 1.4 or later

Works with gojq, the Go implementation of jq

For the specific task defined here, both jq (version 1.4 or later) and gojq should suffice, but for very large integers (greater than 2^53), either gojq or a version of the C implementation of jq with support for very large external integers would be required.

49927398716
49927398717
1234567812345678
1234567812345670
!
Pass
Fail
Fail
Pass


$include "seed7_05.s7i"; const func boolean: luhnTest (in string: cardNumber) is func result var boolean: luhnTest is FALSE; local var integer: index is 0; var integer: digit is 0; var boolean: isOdd is TRUE; var integer: oddSum is 0; var integer: evenSum is 0; begin for index range length(cardNumber) downto 1 do digit := integer parse str(cardNumber[index]); if isOdd then oddSum +:= digit; else evenSum +:= digit div 5 + (2 * digit) rem 10; end if; isOdd := not isOdd; end for; luhnTest := (oddSum + evenSum) rem 10 = 0; end func; const proc: main is func local var string: cardNumber is ""; begin for cardNumber range [] ("49927398716", "49927398717", "1234567812345678", "1234567812345670") do writeln(cardNumber <& ": " <& luhnTest(cardNumber)); end for; end func; Output: 49927398716: TRUE 49927398717: FALSE 1234567812345678: FALSE 1234567812345670: TRUE  ## SenseTalk function LuhnCheck ccNum put length of ccNum into numDigits put the last character of ccNum into total put numDigits modulo 2 into parity repeat for each character of the first numDigits - 1 characters of ccNum put it into digit if (the counter - 1) modulo 2 equals parity multiply digit by 2 end if if digit is greater than 9 subtract 9 from digit end if add digit to total end repeat return total is divisible by 10end LuhnCheck repeat for each item of (49927398716, 49927398717, 1234567812345678, 1234567812345670) put it && LuhnCheck(it)end repeat ## SequenceL  main(args(2)) := sum(luhnTest(asciiToInt(args[1]) - asciiToInt('0'))) mod 10 = 0; s2Mapping := [0,2,4,6,8,1,3,5,7,9]; luhnTest(x(1))[i] := x[i] when i mod 2 = size(x) mod 2 else s2Mapping[x[i] + 1];  ## Shen  (define mapi _ _ [] -> [] F N [X | Xs] -> [(F N X) | (mapi F (+ N 1) Xs)]) (define double X -> (let Y (* 2 X) (if (> Y 9) (- Y 9) Y))) (define luhn? Number -> (let Exploded (explode Number) Digits (map (/. H (- (string->n H) 48)) Exploded) Reversed (reverse Digits) Doubled (mapi (/. N X (if (= 1 (shen.mod N 2)) (double X) X)) 0 Reversed) Summed (sum Doubled) Modded (shen.mod Summed 10) (= 0 Modded))) "Expected: [true false false true]" (map (function luhn?) ["49927398716" "49927398717" "1234567812345678" "1234567812345670"])  Output: mapi transform-x luhn? "Expected: [true false false true]" [true false false true] run time: 0.014999985694885254 secs loaded  ## Sidef func luhn (n) { static a = {|j| (2*j // 10) + (2*j % 10) }.map(^10) var checksum = n.digits.map_kv {|i,j| i.is_odd ? a[j] : j }.sum checksum % 10 == 0} for n in [49927398716, 49927398717, 1234567812345678, 1234567812345670] { say [n, luhn(n)]} Output: [49927398716, true] [49927398717, false] [1234567812345678, false] [1234567812345670, true] ## SNOBOL4 Using a precomputed array.  define('luhn(n)a,d,i,j,sum') :(luhn_end)luhn n = reverse(n); a = array('0:9')ln1 a<i> = (2 * i / 10) + remdr(2 * i,10) i = lt(i,9) i + 1 :s(ln1)ln2 n len(1) . d = :f(ln3) d = ne(remdr(j,2),0) a<d>; j = j + 1 sum = sum + d :(ln2)ln3 luhn = 0; luhn = eq(remdr(sum,10),0) 1 :(return)luhn_end ok = array('0:1') ok<0> = 'FAIL' ok<1> = 'OK' * Test and display define('test(n)') :(test_end)test output = n ': ' ok<luhn(n)> :(return)test_end test('49927398716') test('49927398717') test('1234567812345678') test('1234567812345670')end  Output: 49927398716: OK 49927398717: FAIL 1234567812345678: FAIL 1234567812345670: OK ## SPARK Works with SPARK GPL 2010 and GPS GPL 2010. Based on the Ada version. All code shown to be free of run-time type errors. A final test has been added which passes as valid unless there is an explicit test for all digits. with Spark_IO;--# inherit Spark_IO;--# main_program;procedure Luhn--# global in out Spark_IO.Outputs;--# derives Spark_IO.Outputs from *;is function Luhn_Test (Num : String) return Boolean --# pre Num'Last <= 20; is Sum : Integer := 0; Od : Boolean := True; Int : Integer; X : Integer; OK : Boolean := True; begin for P in reverse Integer range Num'Range loop Int := Character'Pos(Num(P)) - Character'Pos('0'); if Int not in 0 .. 9 then OK := False; exit; end if; X := (((Int*2) mod 10) + (Int / 5)); --# assert Num'Last - P in 0 .. 19 --# and Sum in 0 .. (Num'Last - P) * 10 --# and Int in 0 .. 9 --# and X in 0 .. 10; if Od then Sum := Sum + Int; else Sum := Sum + X; end if; Od := not Od; end loop; return OK and (Sum mod 10) = 0; end Luhn_Test; procedure Do_Test (Num : in String) --# global in out Spark_IO.Outputs; --# derives Spark_IO.Outputs from *, Num; --# pre Num'Last <= 20; is begin Spark_IO.Put_String(Spark_IO.Standard_Output, Num, 16); if Luhn_Test(Num) then Spark_IO.Put_String(Spark_IO.Standard_Output, " is valid.", 0); else Spark_IO.Put_String(Spark_IO.Standard_Output, " is not valid.", 0); end if; Spark_IO.New_Line(Spark_IO.Standard_Output, 1); end Do_Test; begin Do_Test("49927398716"); Do_Test("49927398717"); Do_Test("1234567812345678"); Do_Test("1234567812345670"); Do_Test("123456781234567D");end Luhn; Output: 49927398716 is valid. 49927398717 is not valid. 1234567812345678 is not valid. 1234567812345670 is valid. 123456781234567D is not valid. ## SQL PL Works with: Db2 LUW With SQL PL:  --#SET TERMINATOR @ SET SERVEROUTPUT ON @ CREATE OR REPLACE FUNCTION LUHN_TEST ( IN NUMBER VARCHAR(24) ) RETURNS SMALLINT --) RETURNS BOOLEAN BEGIN DECLARE TYPE CARD_NUMBER AS VARCHAR(1) ARRAY [24]; DECLARE LENGTH SMALLINT; DECLARE REVERSE CARD_NUMBER; DECLARE I SMALLINT; DECLARE POS SMALLINT; DECLARE S1 SMALLINT; DECLARE S2 SMALLINT; DECLARE TEMP SMALLINT; DECLARE RET SMALLINT; --DECLARE RET BOOLEAN; DECLARE INVALID_CHAR CONDITION FOR SQLSTATE 'LUHN1'; -- Reverse the order of the digits in the number. SET LENGTH = LENGTH(NUMBER); SET I = 1; WHILE (I <= LENGTH) DO SET POS = LENGTH - I + 1; SET REVERSE[POS] = SUBSTR(NUMBER, I, 1); IF (ASCII(REVERSE[POS]) < 48 OR 57 < ASCII(REVERSE[POS])) THEN SIGNAL INVALID_CHAR SET MESSAGE_TEXT = 'Invalid character, not a digit'; END IF; SET I = I + 1; END WHILE; -- Take the first, third, ... and every other odd digit in the reversed digits and sum them to form the partial sum s1 SET S1 = 0; SET I = 1; WHILE (I <= LENGTH) DO IF (MOD(I, 2) = 1) THEN SET S1 = S1 + REVERSE[I]; END IF; -- CALL DBMS_OUTPUT.PUT_LINE('I ' || I || ', S1 ' || S1 || ', val ' || REVERSE[I]); SET I = I + 1; END WHILE; -- Taking the second, fourth ... and every other even digit in the reversed digits: SET S2 = 0; SET TEMP = 0; SET I = 1; WHILE (I <= LENGTH) DO IF (MOD(I, 2) = 0) THEN -- Multiply each digit by two and sum the digits if the answer is greater than nine to form partial sums for the even digits SET TEMP = REVERSE[I] * 2; IF (TEMP > 9) THEN SET TEMP = (TEMP / 10) + (MOD(TEMP, 10)); END IF; -- Sum the partial sums of the even digits to form s2 SET S2 = S2 + TEMP; END IF; -- CALL DBMS_OUTPUT.PUT_LINE('I ' || I || ', S2 ' || S2 || ', TEMP ' || TEMP || ' val ' || REVERSE[I]); SET I = I + 1; END WHILE; -- If s1 + s2 ends in zero then the original number is in the form of a valid credit card number as verified by the Luhn test. SET RET = 1; --SET RET = FALSE; SET TEMP = S1 + S2; IF (MOD(TEMP, 10) = 0) THEN SET RET = 0; --SET RET = TRUE; CALL DBMS_OUTPUT.PUT_LINE('It is a valid number ' || S1 || '+' || S2 || '=' || TEMP); ELSE CALL DBMS_OUTPUT.PUT_LINE('It is NOT a valid number ' || S1 || '+' || S2 || '=' || TEMP); END IF; RETURN RET; END@  Output: db2 [email protected] db2 => SET SERVEROUTPUT ON @ DB20000I The SET SERVEROUTPUT command completed successfully. db2 => CREATE OR REPLACE FUNCTION VALIDATE_CREDIT_CARD_NUMBER ( ... db2 (cont.) => END @ DB20000I The SQL command completed successfully. db2 => values VALIDATE_CREDIT_CARD_NUMBER(49927398716)@ 1 ------ 0 1 record(s) selected. It is a valid number 42+28=70 db2 => VALUES VALIDATE_CREDIT_CARD_NUMBER(49927398717)@ 1 ------ 1 1 record(s) selected. It is NOT a valid number 43+28=71 db2 => VALUES VALIDATE_CREDIT_CARD_NUMBER(1234567812345678)@ 1 ------ 1 1 record(s) selected. It is NOT a valid number 40+28=68 db2 => VALUES VALIDATE_CREDIT_CARD_NUMBER(1234567812345670)@ 1 ------ 0 1 record(s) selected. It is a valid number 32+28=60  ## Standard ML local fun revDigits 0 = [] | revDigits n = (n mod 10) :: revDigits (n div 10) fun digitSum n = if n > 9 then digitSum (n div 10 + n mod 10) else n fun luhn_sum [] = 0 | luhn_sum [d] = d | luhn_sum (d::d'::ds) = d + digitSum (2*d') + luhn_sum dsin fun luhn_test n = luhn_sum (revDigits n) mod 10 = 0 val res = map luhn_test [49927398716, 49927398717, 1234567812345678, 1234567812345670];end; (*[opening file "luhn.sml"]> val luhn_test = fn : int -> bool val res = [true, false, false, true] : bool list[closing file "luhn.sml"]*) ## Swift func luhn(_ number: String) -> Bool { return number.reversed().enumerated().map({ let digit = Int(String($0.element))!        let even = $0.offset % 2 == 0 return even ? digit : digit == 9 ? 9 : digit * 2 % 9 }).reduce(0, +) % 10 == 0} luhn("49927398716") // trueluhn("49927398717") // false ## Tcl Based on an algorithmic encoding for the test on Wikipedia. package require Tcl 8.5proc luhn digitString { if {[regexp {[^0-9]}$digitString]} {error "not a number"}    set sum 0    set flip 1    foreach ch [lreverse [split $digitString {}]] { incr sum [lindex { {0 1 2 3 4 5 6 7 8 9} {0 2 4 6 8 1 3 5 7 9} } [expr {[incr flip] & 1}]$ch]    }    return [expr {($sum % 10) == 0}]} Driver: foreach testNumber { 49927398716 49927398717 1234567812345678 1234567812345670} { puts [format "%s is %s"$testNumber \	      [lindex {"NOT valid" "valid"} [luhn $testNumber]]]} Output: 49927398716 is valid 49927398717 is NOT valid 1234567812345678 is NOT valid 1234567812345670 is valid  ## Terraform variable number { type = "string"} locals { digits = reverse(split("", var.number)) count = length(local.digits) odds = [for i in range(local.count): local.digits[i] if i%2==0] evens = [for i in range(local.count): local.digits[i] if i%2==1] s1 = length(flatten([for d in local.odds: range(d)])) doubles = [for d in local.evens: d * 2] partials = [for d in local.doubles: d < 10 ? d : floor(d/10)+d%10] s2 = length(flatten([for p in local.partials: range(p)])) check = (local.s1 + local.s2) % 10} output "valid" { value = local.check == 0} Output: $ terraform apply
var.number
Enter a value: 49927398716

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

valid = true
$TF_VAR_number=49927398717 terraform apply >/dev/null; terraform output valid false$ TF_VAR_number=1234567812345678 terraform apply >/dev/null; terraform output valid
false
$TF_VAR_number=1234567812345670 terraform apply >/dev/null; terraform output valid true ## TI-83 BASIC PROGRAM:LUHN:Disp "ENTER NUMBER":Input Str1:0→S:0→E:For(I,length(Str1),1,-1) :inString("0123456789",sub(Str1,I,1))–1→X :If X<0 :Goto BA :If E≠0 :Then :2X→X :If X>9 :X–9→X :End :X+S→S :not(E)→E:End:If fPart(S/10)=0:Then :Disp "GOOD CARD":Else :Lbl BA :Disp "BAD CARD":End  ## Transact-SQL  CREATE FUNCTION dbo._CreditCardNumCheck( @strCCNum VarChar(40) )RETURNS VarChar(7)ASBEGIN DECLARE @string VarChar(40) = REVERSE(@strCCNum); -- usage: set once, never changed DECLARE @strS2Values VarChar(10) = '0246813579'; -- constant: maps digits to their S2 summed values DECLARE @table TABLE (ID INT, Value INT, S_Value INT); -- ID=digit position. S_Value is used for SUM(). DECLARE @p INT = 0; -- loop counter: position in string -- Convert the reversed string's digits into rows in a table variable, S_Values to be updated afterwards WHILE @p < LEN(@string) BEGIN SET @p = @p+1; INSERT INTO @table (ID,Value,S_Value) VALUES (@p, CONVERT(INT,SUBSTRING(@string,@p,1)), 0); END -- Update S_Value column : the digit's value to be summed (for even-positioned digits this is mapped via @strS2Values) UPDATE @table SET S_Value = CASE WHEN ID % 2 = 1 THEN Value ELSE CONVERT(INT,SUBSTRING(@strS2Values,Value+1,1)) END -- If the SUM of S_Values ends in 0 (modulo 10 = 0) then the CC Number is valid RETURN CASE WHEN (SELECT SUM(S_Value) FROM @table) % 10 = 0 THEN 'Valid' ELSE 'Invalid' ENDEND  ## TUSCRIPT $$MODE TUSCRIPTMODE DATA$$ SET cardnumbers=*499273987164992739871712345678123456781234567812345670$$MODE TUSCRIPT-> collecting information for output-formatSET length=MAX_LENGTH(cardnumbers)SET adjust=length+2 LOOP c=cardnumbers-> ">/" = any digitSET cstring=STRINGS (c,":>/:")SET creverse=REVERSE (cstring)SET s1=evenx2=esum=s2="" LOOP n,oe=creverse SET modrest=MOD(n,2) IF (modrest==0) THEN SET even=oe*2 IF (even>9) THEN SET estring=STRINGS (even,":>/:") SET esum=SUM (estring) SET s2=APPEND (s2,esum) ELSE SET s2=APPEND (s2,even) ENDIF ELSE SET s1=APPEND(s1,oe) ENDIF ENDLOOPSET s1=SUM(s1),s2=SUM(s2)SET checksum=s1+s2SET c=CENTER(c,-adjust)IF (checksum.ew."0") THEN PRINT c,"true"ELSE PRINT c,"false"ENDIFENDLOOP Output: 49927398716 true 49927398717 false 1234567812345678 false 1234567812345670 true  ## TXR @(do (defun luhn (num) (for ((i 1) (sum 0)) ((not (zerop num)) (zerop (mod sum 10))) ((inc i) (set num (trunc num 10))) (let ((dig (mod num 10))) (if (oddp i) (inc sum dig) (let ((dig2 (* 2 dig))) (inc sum (+ (trunc dig2 10) (mod dig2 10)))))))))@(collect :vars nil)@{ccnumber /[0-9]+/}@(output)@ccnumber -> @(if (luhn (int-str ccnumber 10)) "good" "bad")@(end)@(end) $ txr luhn.txr luhn.txt
49927398716 -> good
1234567812345670 -> good

## UNIX Shell

Works with: bash
Works with: ksh
function luhn {  typeset n p s t=('0123456789' '0516273849')  while ((-n<${#1})); do p="${t[n--%2]%${1:n:1}*}" ((s+=${#p}))  done  ((s%10))} for c in 49927398716 49927398717 1234567812345678 1234567812345670; do    if luhn $c; then echo$c is invalid    else        echo $c is valid fidone Notes: • The parameter expansion hack (p=${t…%${1:n:1}};…${#p}…) is an interesting way of converting a set of characters to ordinals. It's highly extensible to larger character sets (e.g. for ISBN and Code 39 checksums).
• Invalid characters are effectively treated as 0s. This is actually useful sometimes for ignoring alphabetic prefixes.
• When attempting to understand the function, remember that n is negative, so it indexes from the end of the input string.
Output:
49927398716 is valid
49927398717 is invalid
1234567812345678 is invalid
1234567812345670 is valid

## Ursala

#import std#import nat luhn = %nP; %np*hxiNCNCS; not remainder\10+ //sum:[email protected] ~&iK27K28TK25 iota10

Some notes on this solution:

• iota10 is the list of natural numbers <0,1,2,3,4,5,6,7,8,9>
• ~&K27 and ~&K28 of iota10 extract the alternate items, respectively <0,2,4,6,8> and <1,3,5,7,9>
• ~&K27K28T iota10 is their concatenation, <0,2,4,6,8,1,3,5,7,9> which is also the list of values obtained by doubling each item of iota10 and taking digit sums
• ~&iK27K28TX iota10 would be the pair (<0,1,2,3,4,5,6,7,8,9>,<0,2,4,6,8,1,3,5,7,9>), but using the reification operator K25 in place of X makes it an executable function taking any item of the left list as an argument and returning the corresponding item of the right.
• The part beginning with // is a function of the form //f a, which can be applied to any argument b to obtain f(a,b). In this case, the f is sum:[email protected], which is equivalent to the composition of two functions sum:-0 and ~&DrlrHK32, and a is the function just obtained by reification.
• The function ~&D by itself takes a pair (a,<b0...bn>) whose right side is a list, and returns the list of pairs <(a,b0)...(a,bn)> (i.e., a copy of a paired with each b). The a here will end up being the aforementioned function.
• ~&DrlrHK32 not only forms such a list of pairs, but operates on each pair thus obtained, alternately applying ~&r and ~&lrH to each pair in sequence, where ~&r simply returns the right side of the pair, and ~&lrH uses the left side as a function, which is applied to the right.
• sum:-0 computes the cumulative sum of a list of natural numbers using the binary sum function, and the reduction operator (:-) with vacuous sum 0.
• The whole thing described up to this point is therefore a function that will take a list of numbers in the range 0 to 9, and compute the summation obtained when doubling and digit summing alternate items.
• The input list to this function is constructed from a single natural number first by %nP, which transforms it to text format in decimal, followed by %np*hxiNCNCS, which reverses the digits, makes a separate text of each, and parses them as individual numbers.
• The output from the function is tested for divisibility by 10 with remainder\10, with the result negated so that zero values map to true and non-zero to false.

usage:

#cast %bL test = luhn* <49927398716,49927398717,1234567812345678,1234567812345670>
Output:
<true,false,false,true>


 Option Explicit Sub Main()  Debug.Print "Number 49927398716 is "; Luhn("49927398716")  Debug.Print "Number 49927398717 is "; Luhn("49927398717")  Debug.Print "Number 1234567812345678 is "; Luhn("1234567812345678")  Debug.Print "Number 1234567812345670 is "; Luhn("1234567812345670")End SubPrivate Function Luhn(Nb As String) As StringDim t$, i&, Summ&, s& t = StrReverse(Nb) For i = 1 To Len(t) Step 2 Summ = Summ + CInt(Mid(t, i, 1)) Next i For i = 2 To Len(t) Step 2 s = 2 * (CInt(Mid(t, i, 1))) If s >= 10 Then Summ = Summ - 9 End If Summ = Summ + s Next i If Summ Mod 10 = 0 Then Luhn = "valid" Else Luhn = "invalid" End IfEnd Function Output: Number 49927398716 is valid Number 49927398717 is invalid Number 1234567812345678 is invalid Number 1234567812345670 is valid ## VBScript Function Luhn_Test(cc) cc = RevString(cc) s1 = 0 s2 = 0 For i = 1 To Len(cc) If i Mod 2 > 0 Then s1 = s1 + CInt(Mid(cc,i,1)) Else tmp = CInt(Mid(cc,i,1))*2 If tmp < 10 Then s2 = s2 + tmp Else s2 = s2 + CInt(Right(CStr(tmp),1)) + 1 End If End If Next If Right(CStr(s1 + s2),1) = "0" Then Luhn_Test = "Valid" Else Luhn_Test = "Invalid" End IfEnd Function Function RevString(s) For i = Len(s) To 1 Step -1 RevString = RevString & Mid(s,i,1) NextEnd Function WScript.Echo "49927398716 is " & Luhn_Test("49927398716")WScript.Echo "49927398717 is " & Luhn_Test("49927398717") WScript.Echo "1234567812345678 is " & Luhn_Test("1234567812345678")WScript.Echo "1234567812345670 is " & Luhn_Test("1234567812345670") Output: 49927398716 is Valid 49927398717 is Invalid 1234567812345678 is Invalid 1234567812345670 is Valid ## Visual Basic Works with: Visual Basic version VB6 Standard Public Function LuhnCheckPassed(ByVal dgts As String) As BooleanDim i As Long, s As Long, s1 As Long dgts = VBA.StrReverse(dgts) For i = 1 To Len(dgts) Step 2 s = s + CInt(Mid$(dgts, i, 1))    Next i    For i = 2 To Len(dgts) Step 2        s1 = 2 * (CInt(Mid$(dgts, i, 1))) If s1 >= 10 Then s = s - 9 End If s = s + s1 Next i LuhnCheckPassed = Not CBool(s Mod 10)End Function Test: Sub Main() Debug.Assert LuhnCheckPassed("49927398716") Debug.Assert Not LuhnCheckPassed("49927398717") Debug.Assert Not LuhnCheckPassed("1234567812345678") Debug.Assert LuhnCheckPassed("1234567812345670")End Sub ## Visual Basic .NET  Imports System.Linq Function ValidLuhn(value As String) Return value.Select(Function(c, i) (AscW(c) - 48) << ((value.Length - i - 1) And 1)).Sum(Function(n) If(n > 9, n - 9, n)) Mod 10 = 0 End Function Sub Main() Console.WriteLine(ValidLuhn("49927398716")) Console.WriteLine(ValidLuhn("49927398717")) Console.WriteLine(ValidLuhn("1234567812345678")) Console.WriteLine(ValidLuhn("1234567812345670")) End Sub  Output: True False False True  ## Vlang Translation of: go const ( input = '499273987164992739871712345678123456781234567812345670' t = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9]) fn luhn(s string) bool { odd := s.len & 1 mut sum := 0 for i, c in s.split('') { if c < '0' || c > '9' { return false } if i&1 == odd { sum += t[c.int()-'0'.int()] } else { sum += c.int() - '0'.int() } } return sum%10 == 0} fn main() { for s in input.split("\n") { println('$s ${luhn(s)}') }} Output: 49927398716 true 49927398717 false 1234567812345678 false 1234567812345670 true  ## Wren Library: Wren-fmt Library: Wren-trait import "/fmt" for Fmtimport "/trait" for Stepped var luhn = Fn.new { |s| // reverse digits s = s[-1..0] // sum the odd digits var s1 = Stepped.new(s, 2).reduce(0) { |sum, d| sum + d.bytes[0] - 48 } // sum two times the even digits var s2 = Stepped.new(s[1..-1], 2).reduce(0) { |sum, d| var d2 = (d.bytes[0] - 48) * 2 return sum + ((d2 > 9) ? d2%10 + 1 : d2) } // check if s1 + s2 ends in zero return (s1 + s2)%10 == 0} var tests = [ "49927398716", "49927398717", "1234567812345678", "1234567812345670"]for (test in tests) { var ans = (luhn.call(test)) ? "pass" : "fail" System.print("%(Fmt.s(-16, test)) -> %(ans)")} Output: 49927398716 -> pass 49927398717 -> fail 1234567812345678 -> fail 1234567812345670 -> pass  ## Xojo Public Function Modulus10(digits As String) as String // // Confirm the digits are really, well, digits // dim validator as new RegEx validator.SearchPattern = "\A\d+\z" if validator.Search( digits ) is nil then // // Raise an exception or something // end if static doublingTable() as string = array( "0", "2", "4", "6", "8", "1", "3", "5", "7", "9" ) dim digitArr() as string = digits.Split( "" ) for i as integer = digitArr.Ubound downto 0 step 2 digitArr( i ) = doublingTable( digitArr( i ).Val ) next dim sum as integer for each digit as string in digitArr sum = sum + digit.Val next dim check as integer = ( sum * 9 ) mod 10 return str( check )End Function Public Function ValidateMod10(digits As String) as Boolean dim checkDigit as string = digits.Right( 1 ) digits = digits.Left( digits.Len - 1 ) return Modulus10( digits ) = checkDigitEnd Function  Output: ValididateMod10( "49927398716" ) = True ValididateMod10( "49927398717" ) = False ValididateMod10( "1234567812345678" ) = False ValididateMod10( "1234567812345670" ) = True  ## XPL0 string 0; \use zero-terminated strings func Valid(Str); \Return 'true' if digits in Str pass Luhn testchar Str;int Len, Sum, I, Dig;[Len:= 0; \find length of Strwhile Str(Len) do Len:= Len+1;Sum:= 0; \sum even and odd digitsfor I:= 0 to Len-1 do \(no need to reverse) [if (I xor Len) and 1 then Sum:= Sum + Str(I) - ^0 else [Dig:= Str(I) - ^0; Dig:= Dig*2; Sum:= Sum + Dig/10 + rem(0); ]; ];return rem(Sum/10) = 0; ]; int Luhn, N;[Luhn:= ["49927398716", "49927398717", "1234567812345678", "1234567812345670"];for N:= 0 to 4-1 do [Text(0, Luhn(N)); Text(0, if Valid(Luhn(N)) then " is valid" else " is not valid"); CrLf(0); ];] Output: 49927398716 is valid 49927398717 is not valid 1234567812345678 is not valid 1234567812345670 is valid  ## zkl fcn luhnTest(n){ 0 == (n.split().reverse().reduce(fcn(s,n,clk){ s + if(clk.next()) n else 2*n%10 + n/5 },0,Walker.cycle(1,0)) %10)} T(49927398716,49927398717,1234567812345678,1234567812345670).apply(luhnTest).println(); Output: L(True,False,False,True)  ## ZX Spectrum Basic 10 LET c$="49927398716": GO SUB 100020 LET c$="49927398717": GO SUB 100030 LET c$="1234567812345678": GO SUB 100040 LET c$="1234567812345670": GO SUB 1000999 STOP 1000 REM *************1001 REM * LUHN TEST *1002 REM *************1010 LET r$=""1020 FOR i=LEN c$TO 1 STEP -11030 LET r$=r$+c$(i)1040 NEXT i1050 LET s1=0: LET s2=01060 FOR i=1 TO LEN r$STEP 21070 LET s1=s1+VAL r$(i)1080 NEXT i1090 FOR i=2 TO LEN r$STEP 21100 LET s2sub=VAL r$(i)*21110 IF s2sub>=10 THEN LET s2sub=1+s2sub-101120 LET s2=s2+s2sub1130 NEXT i1140 LET s$=STR$ (s1+s2)1150 IF s$(LEN s$)="0" THEN PRINT c$;" VALID!": LET retval=1: RETURN 1160 PRINT c$;" INVALID!": LET retval=0: RETURN
Output:
49927398716 VALID!
49927398717 INVALID!
1234567812345678 INVALID!
1234567812345670 VALID!