ISBN13 check digit

From Rosetta Code
Task
ISBN13 check digit
You are encouraged to solve this task according to the task description, using any language you may know.
Task

Validate the check digit of an ISBN-13 code:

  •   Multiply every other digit by  3.
  •   Add these numbers and the other digits.
  •   Take the remainder of this number after division by  10.
  •   If it is  0,   the ISBN-13 check digit is correct.


You might use the following codes for testing:

  •   978-0596528126       (good)
  •   978-0596528120         (bad)
  •   978-1788399081       (good)
  •   978-1788399083         (bad)


Show output here, on this page


See also



11l[edit]

Translation of: Python
F is_isbn13(=n)
   n = n.replace(‘-’, ‘’).replace(‘ ’, ‘’)
   I n.len != 13
      R 0B
   V product = sum(n[(0..).step(2)].map(ch -> Int(ch)))
             + sum(n[(1..).step(2)].map(ch -> Int(ch) * 3))
   R product % 10 == 0

V tests = |‘978-1734314502
            978-1734314509
            978-1788399081
            978-1788399083’.split("\n")

L(t) tests
   print(‘ISBN13 ’t‘ validates ’is_isbn13(t))
Output:
ISBN13 978-1734314502 validates 1B
ISBN13 978-1734314509 validates 0B
ISBN13 978-1788399081 validates 1B
ISBN13 978-1788399083 validates 0B

8080 Assembly[edit]

	org	100h
	jmp	demo
	;;;	---------------------------------------------------------------
	;;;	Check if the string at BC is a valid ISBN-13 code.
	;;;	Carry set if true, clear if not.
isbn13:	lxi	h,0	; HL = accumulator
	mov	d,h	; D = 0 (such that if E=A, DE=A).
	call	isbngc	; Get first character
	rnc		; Carry clear = invalid
	dad	d	; Add to running total once
	call	isbngc	; Get second character
	rnc		; Carry clear = invalid
	dad	d	; Add to running total thrice
	dad	d
	dad	d
	call	isbngc	; Get third character
	rnc		; Carry clear = invalid
	dad	d	; Add to running total once
	ldax	b	; Fourth character should be a dash '-'
	inx	b
	cpi	'-'
	stc		; Clear carry w/o touching other flags
	cmc
	rnz		; If not equal, invalid.
	push	h	; Keep loop counter on stack
	mvi	l,5	; 5 times 2 characters
isbnlp:	xthl		; Accumulator in HL 
	call	isbngc	; Get even character
	jnc	isbnex	; If invalid, stop
	dad	d	; Add to running total thrice
	dad	d
	dad 	d
	call	isbngc	; Get odd character
	jnc	isbnex	; If invalid, stop
	dad	d	; Add to running total once
	xthl		; Loop counter in (H)L
	dcr	l	; Done yet?
	jnz	isbnlp	; If not, do next two characters
	pop	h	; Get accumulator
	lxi	d,-10	; Trial division by ten
isbndv:	dad	d	; Subtract 10
	jc	isbndv 	; Until zero passed
	mov	a,l	; Move low byte to A
	adi	10 	; Add ten back (the mod loop went one step too far)
	rz		; If zero, return (carry will have been set)
	ana	a	; Otherwise, make sure carry is clear
	ret		; And then return 
isbnex:	pop	h	; Test failed - throw away accumulator and return
	ret
isbngc:	ldax	b	; Get character from [BC]
	inx	b	; Increment BC 
	sui	'0'	; Subtract ASCII '0' to get digit value
	cpi	10	; If 10 or higher (unsigned), invalid digit.
	mov	e,a	; Set (D)E = value
	ret
	;;;	---------------------------------------------------------------
	;;;	Demo: see if the CP/M command line contains a valid ISBN13
	;;; 	code.
demo:	lxi	b,82h	; Start of command line argument, skipping first space
	call	isbn13	; Is it valid?
	mvi	c,9	; CP/M print string
	lxi	d,good	; If carry is set, then yes
	jc	5
	lxi	d,bad	; Otherwise, no.
	jmp	5
good:	db	'good$'
bad:	db	'bad$'
Output:
A>isbn13 978-1734314502
good
A>isbn13 978-1734314509
bad
A>isbn13 978-1788399081
good
A>isbn13 978-1788399083
bad

8086 Assembly[edit]

	cpu	8086
	bits	16
	org	100h
section	.text
	jmp	demo
isbn13:	;;;	---------------------------------------------------------------
	;;;	Check if the string at DS:SI is a valid ISBN-13 code.
	;;;	Carry set if true, clear if false.
	xor	dx,dx		; DX = running total
	xor	ah,ah		; Set AH=0 so that AX=AL 
	call	.digit		; Get first digit and add to DX
	call	.digit		; Get second digit and add to DX
	add	dx,ax		; Add to DX twice more
	add	dx,ax
	call	.digit		; Get third digit and add to DX
	lodsb			; Fourth character should be a '-'
	cmp	al,'-'
	jne	.fail 		; If not equal, fail
	mov	cx,5 		; Then loop 5 times for the next 10 digits
.loop:	call	.digit		; Get even digit and add to DX
	add	dx,ax		; Add to running total twice more
	add	dx,ax
	call	.digit		; Get odd digit and add to DX
	loop	.loop		; Do this 5 times
	mov	ax,dx		; Divide running total by 10
	mov	dl,10
	div	dl
	test	ah,ah		; Is the remainder zero?
	jnz	.out		; If not, stop (TEST clears carry)
	stc			; Otherwise, set carry and return
	ret
.digit:	lodsb			; Get first character
	sub	al,'0'		; Subtract ASCII 0 to get digit value
	cmp	al,9		 
	ja	.dfail
	add	dx,ax		; Add to ASCII
	ret
.dfail:	pop	dx		; Remove return pointer for .digit from stack
.fail:	clc			; Failure - clear carry
.out:	ret
	;;;	---------------------------------------------------------------
	;;;	Demo: see if the MS-DOS command line contains a valid ISBN13
	;;;	code.
demo:	mov	si,82h		; Start of command line argument skipping space
	call	isbn13		; Is it valid?
	mov	ah,9		; MS-DOS print string
	mov	dx,good		; If carry is set, it is good
	jc	.print
	mov	dx,bad		; Otherwise, it is bad
.print:	int	21h
	ret
section	.data
good:	db	'good$'
bad: 	db	'bad$'
Output:
C:\>isbn13 978-1734314502
good
C:\>isbn13 978-1734314509
bad
C:\>isbn13 978-1788399081
good
C:\>isbn13 978-1788399083
bad

Action![edit]

INCLUDE "D2:CHARTEST.ACT" ;from the Action! Tool Kit

BYTE FUNC CheckISBN13(CHAR ARRAY t)
  BYTE i,index,sum,v

  sum=0 index=0
  FOR i=1 TO t(0)
  DO
    v=t(i)
    IF IsDigit(v) THEN
      v==-'0
      IF index MOD 2=1 THEN
        v==*3
      FI
      sum==+v
      index==+1
    ELSEIF v#'  AND v#'- THEN
      RETURN (0)
    FI
  OD
  IF index#13 OR sum MOD 10#0 THEN
    RETURN (0)
  FI
RETURN (1)

PROC Test(CHAR ARRAY t)
  BYTE correct

  correct=CheckISBN13(t)
  Print(t) Print(" is ")
  IF correct THEN
    PrintE("correct")
  ELSE
    PrintE("incorrect")
  FI
RETURN

PROC Main()
  Put(125) PutE() ;clear screen

  Test("978-1734314502")
  Test("978-1734314509")
  Test("978-1788399081")
  Test("978-1788399083")
RETURN
Output:

Screenshot from Atari 8-bit computer

978-1734314502 is correct
978-1734314509 is incorrect
978-1788399081 is correct
978-1788399083 is incorrect

Ada[edit]

with Ada.Text_IO;

procedure ISBN_Check is

   function Is_Valid (ISBN : String) return Boolean is
      Odd       : Boolean := True;
      Sum       : Integer := 0;
      Value     : Integer;
   begin
      for I in ISBN'Range loop
         if ISBN (I) in '0' .. '9' then
            Value := Character'Pos (ISBN (I)) - Character'Pos ('0');
            if Odd then
               Sum := Sum + Value;
            else
               Sum := Sum + 3 * Value;
            end if;
            Odd := not Odd;
         end if;
      end loop;
      return Sum mod 10 = 0;
   end Is_Valid;

   procedure Show (ISBN : String) is
      use Ada.Text_IO;
      Valid : constant Boolean := Is_Valid (ISBN);
   begin
      Put (ISBN); Put ("  ");
      Put ((if Valid then "Good" else "Bad"));
      New_Line;
   end Show;
begin
   Show ("978-1734314502");
   Show ("978-1734314509");
   Show ("978-1788399081");
   Show ("978-1788399083");
end ISBN_Check;
Output:
978-1734314502  Good
978-1734314509  Bad
978-1788399081  Good
978-1788399083  Bad

ALGOL 68[edit]

Works with: ALGOL 68G version Any - tested with release 2.8.3.win32
BEGIN # Check some IsBN13 check digits                                         #
    # returns TRUE if the alledged isbn13 has the correct check sum,           #
    #         FALSE otherwise                                                  #
    #         non-digit characters are ignored and there must be 13 digits     #
    PROC check isbn13 = ( STRING isbn13 )BOOL:
         BEGIN
            INT sum          := 0;
            INT digits       := 0;
            BOOL other digit := FALSE;
            FOR pos FROM LWB isbn13 TO UPB isbn13 DO
                IF CHAR c = isbn13[ pos ];
                   c >= "0" AND c <= "9"
                THEN
                    # have another digit                                       #
                    digits +:= 1;
                    sum    +:= ( ABS c - ABS "0" ) * IF other digit THEN 3 ELSE 1 FI;
                    other digit := NOT other digit
                FI
            OD;
            digits = 13 AND sum MOD 10 = 0
         END; # check isbn13 #
    # task test cases #
    []STRING tests    = ( "978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083" );
    []BOOL   expected = (             TRUE,            FALSE,             TRUE,            FALSE );
    FOR pos FROM LWB tests TO UPB tests DO
        BOOL result = check isbn13( tests[ pos ] );
        print( ( tests[ pos ]
               , ": "
               , IF result THEN "good" ELSE "bad" FI
               , IF result = expected[ pos ] THEN "" ELSE " NOT AS EXPECTED" FI
               , newline
               )
             )
    OD
END
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

APL[edit]

Works with: Dyalog APL
check_isbn13{
    13≠⍴n(⎕D)/⍵:0
    0=10|(¨n)+.×131 3
}
Output:
      check_isbn13¨ '978-1734314502' '978-1734314509' '978-1788399081' '978-1788399083'
1 0 1 0

AppleScript[edit]

Composition of pure functions[edit]

-------------------- ISBN13 CHECK DIGIT --------------------

-- isISBN13 :: String -> Bool
on isISBN13(s)
    script digitValue
        on |λ|(c)
            if isDigit(c) then
                {c as integer}
            else
                {}
            end if
        end |λ|
    end script
    
    set digits to concatMap(digitValue, characters of s)
    
    13 = length of digits ¬
        and 0 = sum(zipWith(my mul, digits, cycle({1, 3}))) mod 10
end isISBN13


--------------------------- TEST ---------------------------
on run
    script test
        on |λ|(s)
            {s, isISBN13(s)}
        end |λ|
    end script
    
    map(test, {"978-1734314502", "978-1734314509", ¬
        "978-1788399081", "978-1788399083"})
end run


-------------------- GENERIC FUNCTIONS ---------------------

-- concatMap :: (a -> [b]) -> [a] -> [b]
on concatMap(f, xs)
    set lng to length of xs
    set acc to {}
    tell mReturn(f)
        repeat with i from 1 to lng
            set acc to acc & (|λ|(item i of xs, i, xs))
        end repeat
    end tell
    return acc
end concatMap


-- 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 script
end cycle


-- foldl :: (a -> b -> a) -> a -> [b] -> a
on foldl(f, startValue, xs)
    tell mReturn(f)
        set v to startValue
        set lng to length of xs
        repeat with i from 1 to lng
            set v to |λ|(v, item i of xs, i, xs)
        end repeat
        return v
    end tell
end foldl


-- isDigit :: Char -> Bool
on isDigit(c)
    set n to (id of c)
    48  n and 57  n
end isDigit


-- length :: [a] -> Int
on |length|(xs)
    set c to class of xs
    if list is c or string is c then
        length of xs
    else
        (2 ^ 29 - 1) -- (maxInt - simple proxy for non-finite)
    end if
end |length|


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


-- min :: Ord a => a -> a -> a
on min(x, y)
    if y < x then
        y
    else
        x
    end if
end min


-- mReturn :: First-class m => (a -> b) -> m (a -> b)
on mReturn(f)
    -- 2nd class handler function lifted into 1st class script wrapper. 
    if script is class of f then
        f
    else
        script
            property |λ| : f
        end script
    end if
end mReturn


-- mul (*) :: Num a => a -> a -> a
on mul(a, b)
    a * b
end mul


-- sum :: [Num] -> Num
on sum(xs)
    script add
        on |λ|(a, b)
            a + b
        end |λ|
    end script
    
    foldl(add, 0, xs)
end sum


-- take :: Int -> [a] -> [a]
-- take :: Int -> String -> String
on 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 if
end 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 tell
end zipWith
Output:
{{"978-1734314502", true}, {"978-1734314509", false}, {"978-1788399081", true}, {"978-1788399083", false}}

Straightforward[edit]

This task can be tackled very simply by working through the numeric text two characters at a time:

on validateISBN13(ISBN13)
    if (ISBN13's class is not text) then return false
    
    set astid to AppleScript's text item delimiters
    set AppleScript's text item delimiters to {"-", space}
    set ISBN13 to ISBN13's text items
    set AppleScript's text item delimiters to ""
    set ISBN13 to ISBN13 as text
    set AppleScript's text item delimiters to astid
    
    if (((count ISBN13) is not 13) or (ISBN13 contains ".") or (ISBN13 contains ",")) then return false
    try
        ISBN13 as number
    on error
        return false
    end try
    
    set sum to 0
    repeat with i from 1 to 12 by 2
        set sum to sum + (character i of ISBN13) + (character (i + 1) of ISBN13) * 3 -- Automatic text-to-number coercions.
    end repeat
    
    return ((sum + (character 13 of ISBN13)) mod 10 = 0)
end validateISBN13

-- Test:
set output to {}
set verdicts to {"bad", "good"}
repeat with thisISBN13 in {"978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"}
    set isValid to validateISBN13(thisISBN13)
    set end of output to thisISBN13 & ": " & item ((isValid as integer) + 1) of verdicts
end repeat

set astid to AppleScript's text item delimiters
set AppleScript's text item delimiters to linefeed
set output to output as text
set AppleScript's text item delimiters to astid
return output
Output:
"978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad"

Or it can be handled purely numerically. Since the "weights" alternate and are palindromic, it makes no difference whether the last digit or the first is treated as the check digit. In fact, if preferred, the repeat below can go round 7 times with the return line as simply: return (sum mod 10 = 0).

on validateISBN13(ISBN13)
    if (ISBN13's class is not text) then return false
    
    set astid to AppleScript's text item delimiters
    set AppleScript's text item delimiters to {"-", space}
    set ISBN13 to ISBN13's text items
    set AppleScript's text item delimiters to ""
    set ISBN13 to ISBN13 as text
    set AppleScript's text item delimiters to astid
    
    if (((count ISBN13) is not 13) or (ISBN13 contains ".") or (ISBN13 contains ",")) then return false
    try
        set ISBN13 to ISBN13 as number
    on error
        return false
    end try
    
    set sum to 0
    repeat 6 times
        set sum to sum + ISBN13 mod 10 + ISBN13 mod 100 div 10 * 3
        set ISBN13 to ISBN13 div 100
    end repeat
    
    return ((sum + ISBN13) mod 10 = 0)
end validateISBN13

Arturo[edit]

validISBN?: function [isbn][
    currentCheck: to :integer to :string last isbn
    isbn: map split chop replace isbn "-" "" 'd -> to :integer d

    s: 0
    loop.with:'i isbn 'n [
        if? even? i -> s: s + n
        else -> s: s + 3*n
    ]
    checkDigit: 10 - s % 10
    return currentCheck = checkDigit
]

tests: [
    "978-1734314502" "978-1734314509"
    "978-1788399081" "978-1788399083"
]

loop tests 'test [
    print [test "=>" validISBN? test]
]
Output:
978-1734314502 => true 
978-1734314509 => false 
978-1788399081 => true 
978-1788399083 => false

AutoHotkey[edit]

ISBN13_check_digit(n){
	for i, v in StrSplit(RegExReplace(n, "[^0-9]"))
		sum += !Mod(i, 2) ? v*3 : v
	return n "`t" (Mod(sum, 10) ? "(bad)" : "(good)")
}
Examples:
output := ""
nums := ["978-1734314502","978-1734314509","978-1788399081","978-1788399083"]
for i, n in nums
	output .= ISBN13_check_digit(n) "`n"
MsgBox % output
return
Output:
978-1734314502	(good)
978-1734314509	(bad)
978-1788399081	(good)
978-1788399083	(bad)

AWK[edit]

# syntax: GAWK -f ISBN13_CHECK_DIGIT.AWK
BEGIN {
    arr[++n] = "978-1734314502"
    arr[++n] = "978-1734314509"
    arr[++n] = "978-1788399081"
    arr[++n] = "978-1788399083"
    arr[++n] = "9780820424521"
    arr[++n] = "0820424528"
    for (i=1; i<=n; i++) {
      printf("%s %s\n",arr[i],isbn13(arr[i]))
    }
    exit(0)
}
function isbn13(isbn,  check_digit,i,sum) {
    gsub(/[ -]/,"",isbn)
    if (length(isbn) != 13) { return("NG length") }
    for (i=1; i<=12; i++) {
      sum += substr(isbn,i,1) * (i % 2 == 1 ? 1 : 3)
    }
    check_digit = 10 - (sum % 10)
    return(substr(isbn,13,1) == check_digit ? "OK" : sprintf("NG check digit S/B %d",check_digit))
}
Output:
978-1734314502 OK
978-1734314509 NG check digit S/B 2
978-1788399081 OK
978-1788399083 NG check digit S/B 1
9780820424521 OK
0820424528 NG length

BCPL[edit]

get "libhdr"

let checkISBN(s) = valof
$(  let tally = 0
    unless s%0 = 14 resultis false
    unless s%4 = '-' resultis false 
    
    for i=1 to 3
    $(  let digit = s%i-'0'
        test i rem 2 = 0 
            do tally := tally + 3 * digit
            or tally := tally + digit
    $)
    
    for i=5 to 14
    $(  let digit = s%i-'0'
        test i rem 2 = 0
            do tally := tally + digit
            or tally := tally + 3 * digit
    $)
    
    resultis tally rem 10 = 0
$)

let show(s) be
    writef("%S: %S*N", s, checkISBN(s) -> "good", "bad")

let start() be
$(  show("978-1734314502")
    show("978-1734314509")
    show("978-1788399081")
    show("978-1788399083")
$)
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

C[edit]

#include <stdio.h>

int check_isbn13(const char *isbn) {
    int ch = *isbn, count = 0, sum = 0;
    /* check isbn contains 13 digits and calculate weighted sum */
    for ( ; ch != 0; ch = *++isbn, ++count) {
        /* skip hyphens or spaces */
        if (ch == ' ' || ch == '-') {
            --count;
            continue;
        }
        if (ch < '0' || ch > '9') {
            return 0;
        }
        if (count & 1) {
            sum += 3 * (ch - '0');
        } else {
            sum += ch - '0';
        }
    }
    if (count != 13) return 0;
    return !(sum%10);
}

int main() {
    int i;
    const char* isbns[] = {"978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"};
    for (i = 0; i < 4; ++i) {
        printf("%s: %s\n", isbns[i], check_isbn13(isbns[i]) ? "good" : "bad");
    }
    return 0;
}
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

C++[edit]

Translation of: C
#include <iostream>

bool check_isbn13(std::string isbn) {
    int count = 0;
    int sum = 0;

    for (auto ch : isbn) {
        /* skip hyphens or spaces */
        if (ch == ' ' || ch == '-') {
            continue;
        }
        if (ch < '0' || ch > '9') {
            return false;
        }
        if (count & 1) {
            sum += 3 * (ch - '0');
        } else {
            sum += ch - '0';
        }
        count++;
    }

    if (count != 13) {
        return false;
    }
    return sum % 10 == 0;
}

int main() {
    auto isbns = { "978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083" };
    for (auto isbn : isbns) {
        std::cout << isbn << ": " << (check_isbn13(isbn) ? "good" : "bad") << '\n';
    }

    return 0;
}
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

C#[edit]

using System;
using System.Linq;

public class Program
{
    public static void Main() {
        Console.WriteLine(CheckISBN13("978-1734314502"));
        Console.WriteLine(CheckISBN13("978-1734314509"));
        Console.WriteLine(CheckISBN13("978-1788399081"));
        Console.WriteLine(CheckISBN13("978-1788399083"));

        static bool CheckISBN13(string code) {
            code = code.Replace("-", "").Replace(" ", "");
            if (code.Length != 13) return false;
            int sum = 0;
            foreach (var (index, digit) in code.Select((digit, index) => (index, digit))) {
                if (char.IsDigit(digit)) sum += (digit - '0') * (index % 2 == 0 ? 1 : 3);
                else return false;
            }
            return sum % 10 == 0;
        }
    }
}
Output:
True
False
True
False

CLU[edit]

isbn13_check = proc (s: string) returns (bool)
    if string$size(s) ~= 14 then return(false) end
    if s[4] ~= '-' then return(false) end
    begin
        check: int := 0
        for i: int in int$from_to(1, 14) do
            if i=4 then continue end
            d: int := int$parse(string$c2s(s[i]))
            if i=2 cor (i>4 cand i//2=1) then d := d*3 end
            check := check + d
        end
        return(check//10 = 0)
    end except when bad_format: 
        return(false)
    end
end isbn13_check

start_up = proc ()
    po: stream := stream$primary_output()
    tests: array[string] := array[string]$
       ["978-1734314502",
        "978-1734314509",
        "978-1788399081",
        "978-1788399083"]
        
    for test: string in array[string]$elements(tests) do
        stream$puts(po, test)
        stream$puts(po, ": ")
        if isbn13_check(test)
            then stream$putl(po, "good")
            else stream$putl(po, "bad")
        end
    end
end start_up
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

COBOL[edit]

Works with: GnuCOBOL
      ******************************************************************
      * Author: Jay Moseley
      * Date: November 10, 2019
      * Purpose: Testing various subprograms/ functions.
      * Tectonics: cobc -xj testSubs.cbl
      ******************************************************************
       IDENTIFICATION DIVISION.

       PROGRAM-ID. testSubs.
       ENVIRONMENT DIVISION.

       CONFIGURATION SECTION.
       REPOSITORY.
           FUNCTION ALL INTRINSIC
           FUNCTION validISBN13.

       INPUT-OUTPUT SECTION.
       FILE-CONTROL.

       DATA DIVISION.

       FILE SECTION.

       WORKING-STORAGE SECTION.

       01  IX                          PIC S9(4) COMP.
       01  TEST-ISBNS.
           02  FILLER                  PIC X(14) VALUE '978-1734314502'.
           02  FILLER                  PIC X(14) VALUE '978-1734314509'.
           02  FILLER                  PIC X(14) VALUE '978-1788399081'.
           02  FILLER                  PIC X(14) VALUE '978-1788399083'.
       01  TEST-ISBN                   REDEFINES TEST-ISBNS
                                       OCCURS 4 TIMES
                                       PIC X(14).

       PROCEDURE DIVISION.

       MAIN-PROCEDURE.

           PERFORM 
             VARYING IX 
             FROM 1
             BY 1
             UNTIL IX > 4

             DISPLAY TEST-ISBN (IX) '   ' WITH NO ADVANCING
             END-DISPLAY
             IF validISBN13(TEST-ISBN (IX)) = -1
               DISPLAY '(bad)'
             ELSE
               DISPLAY '(good)'
             END-IF

           END-PERFORM.

           GOBACK.

       END PROGRAM testSubs.

      ******************************************************************
      * Author: Jay Moseley
      * Date: May 19, 2016
      * Purpose: validate ISBN-13 (International Standard
      *          Book Number).
      ******************************************************************
       IDENTIFICATION DIVISION.

       FUNCTION-ID. validISBN13.
       ENVIRONMENT DIVISION.

       CONFIGURATION SECTION.
       REPOSITORY.
           FUNCTION ALL INTRINSIC.

       INPUT-OUTPUT SECTION.
       FILE-CONTROL.

       DATA DIVISION.

       FILE SECTION.

       WORKING-STORAGE SECTION.

       01  PASSED-SIZE                 PIC S9(6) COMP-5.
       01  IX                          PIC S9(4) COMP.

       01  WORK-FIELDS.
           02  WF-DIGIT                PIC X.
           02  WF-COUNT                PIC 9(2).
               88  WEIGHT-1  VALUE 1, 3, 5, 7, 9, 11, 13.
               88  WEIGHT-3  VALUE 2, 4, 6, 8, 10, 12.
           02  WF-SUM                  PIC S9(8) COMP.

       LINKAGE SECTION.

       01  PASSED-ISBN                 PIC X ANY LENGTH.
       01  RETURN-VALUE                PIC S9.

       PROCEDURE DIVISION USING PASSED-ISBN
                          RETURNING RETURN-VALUE.

           CALL 'C$PARAMSIZE'
             USING 1
             GIVING PASSED-SIZE
           END-CALL.
       
       COMPUTE-CKDIGIT.

           INITIALIZE WORK-FIELDS.
           PERFORM 
             VARYING IX 
             FROM 1 
             BY 1
             UNTIL IX GREATER THAN PASSED-SIZE

               MOVE PASSED-ISBN (IX:1) TO WF-DIGIT
               IF WF-DIGIT IS NUMERIC
                 ADD 1 TO WF-COUNT
                 IF WEIGHT-1
                   ADD NUMVAL(WF-DIGIT) TO WF-SUM
                 ELSE
                   COMPUTE WF-SUM = WF-SUM + 
                     (NUMVAL(WF-DIGIT) * 3)
                   END-COMPUTE
                 END-IF
               END-IF

           END-PERFORM.

           IF MOD(WF-SUM, 10) = 0
             MOVE +0 TO RETURN-VALUE
           ELSE
             MOVE -1 TO RETURN-VALUE
           END-IF.

           GOBACK.
      * - - - - - - - - - - - - - - - - - - - - - - PROGRAM EXIT POINT

       END FUNCTION validISBN13.
Output:
978-1734314502   (good)
978-1734314509   (bad)
978-1788399081   (good)
978-1788399083   (bad)

Cowgol[edit]

include "cowgol.coh";
 
sub check_isbn13(isbn: [uint8]): (r: uint8) is  
    var n: uint8 := 0;
    r := 0;
    loop    
        var c := [isbn];
        isbn := @next isbn;
        if c == 0 then break; end if;
        c := c - '0';
        if c <= 9 then
            r := r + c;
            n := n + 1;
            if (n & 1) == 0 then
                r := r + c * 2;
            end if;
        end if;
    end loop;
    if n == 13 and r%10 == 0 then
        r := 1;
    else
        r := 0;
    end if;
end sub;
 
var isbns: [uint8][] := {
    "978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"
};
 
var result: [uint8][] := {": bad\n", ": good\n"};
 
var n: uint8 := 0;
while n < @sizeof isbns loop
    print(isbns[n]);
    print(result[check_isbn13(isbns[n])]);
    n := n + 1;
end loop;
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

D[edit]

Translation of: Kotlin
import std.stdio;

bool isValidISBN13(string text) {
    int sum, i;
    foreach (c; text) {
        if ('0' <= c && c <= '9') {
            int value = c - '0';
            if (i % 2 == 0) {
                sum += value;
            } else {
                sum += 3 * value;
            }

            i++;
        }
    }
    return i == 13 && 0 == sum % 10;
}

unittest {
    assert(isValidISBN13("978-1734314502"));
    assert(!isValidISBN13("978-1734314509"));
    assert(isValidISBN13("978-1788399081"));
    assert(!isValidISBN13("978-1788399083"));
}

Draco[edit]

proc nonrec isbn13_check(*char isbn) bool:
    byte n, check, d;
    char cur;
    bool ok;
    n := 0;
    check := 0;
    ok := true;
    while
        cur := isbn*;
        isbn := isbn + 1;
        ok and cur ~= '\e'
    do
        if n=3 then
            if cur ~= '-' then ok := false fi
        elif cur<'0' or cur>'9' then
            ok := false
        else
            d := cur - '0';
            if n=1 or (n>3 and n&1 = 0) then
                d := d * 3;
            fi;
            check := check + d
        fi;
        n := n + 1
    od;
    ok and n = 14 and check%10 = 0
corp

proc nonrec test(*char isbn) void:
    writeln(isbn, ": ", 
            if isbn13_check(isbn) then "good" else "bad" fi)
corp

proc nonrec main() void:
    test("978-1734314502");
    test("978-1734314509");
    test("978-1788399081");
    test("978-1788399083")
corp
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

Excel[edit]

LAMBDA[edit]

Binding the name ISBN13Check to the following lambda expression in the Name Manager of the Excel WorkBook:

(See LAMBDA: The ultimate Excel worksheet function)

ISBN13Check
=LAMBDA(s,
    LET(
        ns, FILTERP(
            LAMBDA(v,
                NOT(ISERROR(v))
            )
        )(
            VALUE(CHARSROW(s))
        ),
        ixs, SEQUENCE(
            1, COLUMNS(ns),
            1, 1
        ),

        0 = MOD(
            SUM(
                IF(0 <> MOD(ixs, 2),
                    INDEX(ns, ixs),
                    3 * INDEX(ns, ixs)
                )
            ),
            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
    )
)


FILTERP
=LAMBDA(p,
    LAMBDA(xs,
        FILTER(xs, p(xs))
    )
)


ISDIGIT
=LAMBDA(c,
    LET(
        ic, CODE(c),

        AND(47 < ic, 58 > ic)
    )
)
Output:
fx =ISBN13Check(A2)
A B
1 Candidate string ISBN13 checked
2 978-1734314502 TRUE
3 978-1734314509 FALSE
4 978-1788399081 TRUE
5 978-1788399083 FALSE

Factor[edit]

USING: combinators.short-circuit formatting kernel math
math.functions math.parser math.vectors qw sequences
sequences.extras sets unicode ;

: (isbn13?) ( str -- ? )
    string>digits
    [ <evens> sum ] [ <odds> 3 v*n sum + ] bi 10 divisor? ;

: isbn13? ( str -- ? )
    "- " without
    { [ length 13 = ] [ [ digit? ] all? ] [ (isbn13?) ] } 1&& ;

qw{ 978-1734314502 978-1734314509 978-1788399081 978-1788399083 }
[ dup isbn13? "good" "bad" ? "%s: %s\n" printf ] each
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

Forth[edit]

The following word not only identifies correct 13 digit ISBN (and EAN) codes, but also 8 digit EAN and GTIN codes.

: is-digit [char] 0 - 10 u< ;

: isbn?                                ( a n -- f)
  1- chars over + 2>r 0 1 2r> ?do
    dup i c@ dup is-digit              \ get length and factor, setup loop
    if [char] 0 - * rot + swap 3 * 8 mod else drop drop then
  -1 chars +loop drop 10 mod 0=        \ now calculate checksum
;
Output:

In Forth, a "true" value is indicated by "-1".

s" 978-1734314502" isbn? .  -1  ok
s" 978-1734314509" isbn? .  0  ok
s" 978-1788399081" isbn? .  -1  ok
s" 978-1788399083" isbn? .  0  ok

Fortran[edit]

program isbn13
    implicit none

    character(len=14), dimension(4), parameter  :: isbns=["978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"]
    integer                                     :: i

    do i = 1, ubound(isbns, 1)
        if (check_isbn13(isbns(i))) then
            print*, isbns(i), " : ", "good"
        else
            print*, isbns(i), " : ", "bad"
        end if
    end do
contains
    pure function check_isbn13(isbn)
        character(len=*), intent(in)    :: isbn
        logical                         :: check_isbn13
        integer                         :: summ, counter, i, digit

        check_isbn13 = .false.
        counter = 0
        summ = 0

        do i = 1, len(isbn)
            if (isbn(i:i) == ' ' .or. isbn(i:i) == '-') cycle
            counter = counter + 1
            read(isbn(i:i), '(I1)') digit
            if (modulo(counter, 2) == 0) then
                summ = summ + 3*digit
            else
                summ = summ + digit
            end if
        end do
        if (counter == 13 .and. modulo(summ, 10) == 0) check_isbn13 = .true.
    end function check_isbn13
end program isbn13
Output:
 978-1734314502 : good
 978-1734314509 : bad
 978-1788399081 : good
 978-1788399083 : bad

FreeBASIC[edit]

#define ZEROC asc("0")

function is_num( byval c as string ) as boolean
    if asc(c) >= ZEROC andalso asc(c)<ZEROC+10 then return true
    return false
end function

function is_good_isbn( isbn as string ) as boolean
    dim as uinteger charno = 0, digitno = 0, sum = 0
    dim as string*1 currchar
    while charno <= len(isbn)
        currchar = mid(isbn,charno,1)
        if is_num(currchar) then
            if digitno mod 2 = 1 then
                sum += 2*(asc(currchar)-ZEROC)
            end if
            sum += asc(currchar)-ZEROC
            digitno += 1
        end if
        charno += 1
    wend
    if sum mod 10 = 0 then 
        return true
    else 
        return false
    end if
end function

dim as string isbns(0 to 3) = { "978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083" }
dim as uinteger i
for i = 0 to 3
    if is_good_isbn( isbns(i) ) then
        print isbns(i)+": good"
    else
        print isbns(i)+": bad"
    end if
next i
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

F#[edit]

// ISBN13 Check Digit
open System

let parseInput (input: string) =
    Seq.map(fun c -> c |> string) input |> Seq.toList |> List.map(fun x -> Int32.Parse x)

[<EntryPoint>]
let main argv =
    let isbnnum = parseInput (String.filter (fun x -> x <> '-') argv.[0])
    // Multiply every other digit by 3
    let everyOther = List.mapi (fun i x -> if i % 2 = 0 then x * 3 else x) isbnnum
    // Sum the *3 list with the original list
    let sum = List.sum everyOther + List.sum isbnnum
    // If the remainder of sum / 10 is 0 then it's a valid ISBN13
    if sum % 10 = 0 then
        printfn "%s Valid ISBN13" argv.[0]
    else
        printfn "%s Invalid ISBN13" argv.[0]
    0
Output:
978-1734314502 Valid ISBN13
978-1734314509 Inalid ISBN13
978-1788399081 Valid ISBN13
978-1788399083 Inalid ISBN13

Fōrmulæ[edit]

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

Programs in Fōrmulæ are created/edited online in its website, However they run on execution servers. By default remote servers are used, but they are limited in memory and processing power, since they are intended for demonstration and casual use. A local server can be downloaded and installed, it has no limitations (it runs in your own computer). Because of that, example programs can be fully visualized and edited, but some of them will not run if they require a moderate or heavy computation/memory resources, and no local server is being used.

In this page you can see the program(s) related to this task and their results.

Go[edit]

package main

import (
    "fmt"
    "strings"
    "unicode/utf8"
)

func checkIsbn13(isbn string) bool {
    // remove any hyphens or spaces
    isbn = strings.ReplaceAll(strings.ReplaceAll(isbn, "-", ""), " ", "")
    // check length == 13
    le := utf8.RuneCountInString(isbn)
    if le != 13 {
        return false
    }
    // check only contains digits and calculate weighted sum
    sum := int32(0)
    for i, c := range isbn {
        if c < '0' || c > '9' {
            return false
        }
        if i%2 == 0 {
            sum += c - '0'
        } else {
            sum += 3 * (c - '0')
        }
    }
    return sum%10 == 0
}

func main() {
    isbns := []string{"978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"}
    for _, isbn := range isbns {
        res := "bad"
        if checkIsbn13(isbn) {
            res = "good"
        }
        fmt.Printf("%s: %s\n", isbn, res)
    }
}
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

Haskell[edit]

import Data.Char (digitToInt, isDigit)
import Text.Printf (printf)

pair :: Num a => [a] -> [(a, a)]
pair [] = []
pair xs = p (take 2 xs) : pair (drop 2 xs)
  where
    p ps = case ps of
      (x : y : zs) -> (x, y)
      (x : zs) -> (x, 0)

validIsbn13 :: String -> Bool
validIsbn13 isbn
  | length (digits isbn) /= 13 = False
  | otherwise = calc isbn `rem` 10 == 0
  where
    digits = map digitToInt . filter isDigit
    calc = sum . map (\(x, y) -> x + y * 3) . pair . digits

main :: IO ()
main =
  mapM_
    (printf "%s: Valid: %s\n" <*> (show . validIsbn13))
    [ "978-1734314502",
      "978-1734314509",
      "978-1788399081",
      "978-1788399083"
    ]
Output:
978-1734314502: Valid: True
978-1734314509: Valid: False
978-1788399081: Valid: True
978-1788399083: Valid: False

Or, expressed in terms of cycle:

import Data.Char (digitToInt, isDigit)

isISBN13 :: String -> Bool
isISBN13 =
  (0 ==)
    . flip rem 10
    . sum
    . flip
      (zipWith ((*) . digitToInt) . filter isDigit)
      (cycle [1, 3])

main :: IO ()
main =
  mapM_
    (print . ((,) <*> isISBN13))
    [ "978-1734314502",
      "978-1734314509",
      "978-1788399081",
      "978-1788399083"
    ]
Output:
("978-1734314502",True)
("978-1734314509",False)
("978-1788399081",True)
("978-1788399083",False)

IS-BASIC[edit]

100 PROGRAM "ISBN13.bas"
110 DO
120   PRINT :INPUT PROMPT "ISBN-13 code: ":IS$
130   IF IS$="" THEN EXIT DO
140   IF ISBN(IS$) THEN
150     PRINT "Ok."
160   ELSE
170     PRINT "CRC error."
180   END IF
190 LOOP
200 DEF TRIM$(S$)
210   LET T$=""
220   FOR I=1 TO LEN(S$)
230     IF S$(I)>CHR$(47) AND S$(I)<CHR$(58) THEN LET T$=T$&S$(I)
240   NEXT
250   LET TRIM$=T$
260 END DEF
270 DEF ISBN(S$)
280   LET SUM,ISBN=0:LET ISBN$=TRIM$(IS$)
290   IF LEN(ISBN$)<>13 THEN PRINT "Invalid length.":EXIT DEF
300   FOR I=1 TO 11 STEP 2
310     LET SUM=SUM+VAL(ISBN$(I))+VAL(ISBN$(I+1))*3
320   NEXT
330   LET SUM=SUM+VAL(ISBN$(13))
340   IF MOD(SUM,10)=0 THEN LET ISBN=-1
350 END DEF

J[edit]

   D            =:  '0123456789'
   
   isbn13c      =:  D&([ check@:i. clean)
     check      =:  0 = 10 | lc
       lc       =:  [ +/@:* weight
         weight =:  1 3 $~ #
     clean      =:  ] -. a. -. [
Output:
   isbn13c;._1 ' 978-1734314502 978-1734314509 978-1788399081 978-1788399083'
1 0 1 0

Java[edit]

public static void main(){
        System.out.println(isISBN13("978-1734314502"));
        System.out.println(isISBN13("978-1734314509"));
        System.out.println(isISBN13("978-1788399081"));
        System.out.println(isISBN13("978-1788399083"));
    }
public static boolean isISBN13(String in){
        int pre = Integer.parseInt(in.substring(0,3));
        if (pre!=978)return false;
        String postStr = in.substring(4);
        if (postStr.length()!=10)return false;
        int post = Integer.parseInt(postStr);
        int sum = 38;
        for(int x = 0; x<10;x+=2)
        sum += (postStr.charAt(x)-48)*3 + ((postStr.charAt(x+1)-48));
        if(sum%10==0) return true;
        return false;
    }
Output:
true
false
true
false

jq[edit]

Works with: jq

Works with gojq, the Go implementation of jq

def isbn_check:
  def digits: tostring | explode | map( select(. >= 48 and . <= 57) | [.] | implode | tonumber);
  def sum(s): reduce s as $x (null; . + $x);
  digits
  | . as $digits
  |      sum(range(0;length;2) | $digits[.]) as $one
  | (3 * sum(range(1;length;2) | $digits[.])) as $two
  | (($one+$two) % 10) == 0;

def testingcodes:
 ["978-1734314502", "978-1734314509",
  "978-1788399081", "978-1788399083"];
 
testingcodes[]
| "\(.): \(if isbn_check then "good" else "bad" end)"
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

Julia[edit]

function isbncheck(str)
    return sum(iseven(i) ? 3 * parse(Int, ch) : parse(Int, ch) 
        for (i, ch) in enumerate(replace(str, r"\D" => ""))) % 10 == 0
end

const testingcodes = ["978-1734314502", "978-1734314509",
                      "978-1788399081", "978-1788399083"]

for code in testingcodes
    println(code, ": ", isbncheck(code) ? "good" : "bad")
end
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

Kotlin[edit]

fun isValidISBN13(text: String): Boolean {
    val isbn = text.replace(Regex("[- ]"), "")
    return isbn.length == 13 && isbn.map { it - '0' }
        .mapIndexed { index, value -> when (index % 2) { 0 -> value else -> 3 * value } }
        .sum() % 10 == 0
}

Tested using Spek

describe("ISBN Utilities") {
    mapOf(
        "978-1734314502" to true,
        "978-1734314509" to false,
        "978-1788399081" to true,
        "978-1788399083" to false
    ).forEach { (input, expected) ->
        it("returns $expected for $input") {
            println("$input: ${when(isValidISBN13(input)) { 
                true -> "good"
                else -> "bad"
            }}")
            assert(isValidISBN13(input) == expected)
        }
    }
}
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

langur[edit]

Works with: langur version 0.8.11

In this example, we map to multiple functions (actually 1 no-op).

val .isbn13checkdigit = f(var .s) {
    .s = replace(.s, RE/[\- ]/)
    matching(re/^[0-9]{13}$/, .s) and
        fold(f{+}, map [_, f{x 3}], s2n .s) div 10
}

val .tests = h{
    "978-0596528126": true,
    "978-0596528120": false,
    "978-1788399081": true,
    "978-1788399083": false,
}

for .key of .tests {
    val .pass = .isbn13checkdigit(.key)
    write .key, ": ", if(.pass: "good"; "bad")
    writeln if(.pass == .tests[.key]: ""; " (ISBN-13 CHECK DIGIT TEST FAILED)")
}
Works with: langur version 0.9.0

In this example, we set a for loop value as it progresses.

val .isbn13checkdigit = f(var .s) {
    .s = replace(.s, RE/[\- ]/)
    var .alt = true
    matching(re/^[0-9]{13}$/, .s) and
        for[=0] .d in s2n(.s) { _for += if(not= .alt: .d x 3; .d) } div 10
}

val .tests = h{
    "978-0596528126": true,
    "978-0596528120": false,
    "978-1788399081": true,
    "978-1788399083": false,
}

for .key of .tests {
    val .pass = .isbn13checkdigit(.key)
    write .key, ": ", if(.pass: "good"; "bad")
    writeln if(.pass == .tests[.key]: ""; " (ISBN-13 CHECK DIGIT TEST FAILED)")
}
Output:
978-0596528126: good
978-0596528120: bad
978-1788399081: good
978-1788399083: bad

Lua[edit]

Translation of: C
function checkIsbn13(isbn)
    local count = 0
    local sum = 0
    for c in isbn:gmatch"." do
        if c == ' ' or c == '-' then
            -- skip
        elseif c < '0' or '9' < c then
            return false
        else
            local digit = c - '0'
            if (count % 2) > 0 then
                sum = sum + 3 * digit
            else
                sum = sum + digit
            end
            count = count + 1
        end
    end

    if count ~= 13 then
        return false
    end
    return (sum % 10) == 0
end

function test(isbn)
    if checkIsbn13(isbn) then
        print(isbn .. ": good")
    else
        print(isbn .. ": bad")
    end
end

function main()
    test("978-1734314502")
    test("978-1734314509")
    test("978-1788399081")
    test("978-1788399083")
end

main()
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad


Mathematica / Wolfram Language[edit]

ClearAll[ValidISBNQ]
ValidISBNQ[iban_String] := Module[{i},
  i = StringReplace[iban, {" " -> "", "-" -> ""}];
  If[StringMatchQ[i, Repeated[DigitCharacter]],
   i = ToExpression /@ Characters[i];
   i[[2 ;; ;; 2]] *= 3;
   Mod[Total[i], 10] == 0
   ,
   False
   ]
  ]
ValidISBNQ["978-1734314502"]
ValidISBNQ["978-1734314509"]
ValidISBNQ["978-1788399081"]
ValidISBNQ["978-1788399083"]
Output:
True
False
True
False


Modula-2[edit]

MODULE ISBN;
FROM InOut IMPORT WriteString, WriteLn;
FROM Strings IMPORT Length;

PROCEDURE validISBN(s: ARRAY OF CHAR): BOOLEAN;
    VAR total, i, length: CARDINAL;
BEGIN
    total := 0;
    length := Length(s);
    IF (length # 14) OR (s[3] # '-') THEN
        RETURN FALSE;
    END;
    FOR i := 0 TO length-1 DO
        IF i # 3 THEN
            IF (s[i] < '0') OR (s[i] > '9') THEN
                RETURN FALSE;
            ELSIF (i < 3) AND (i MOD 2 = 1) OR (i > 3) AND (i MOD 2 = 0) THEN
                total := total + 3 * (ORD(s[i]) - ORD('0'));
            ELSE
                total := total + ORD(s[i]) - ORD('0');
            END;
        END;
    END;
    RETURN total MOD 10 = 0;
END validISBN;

PROCEDURE check(s: ARRAY OF CHAR);
BEGIN
    WriteString(s);
    WriteString(': ');
    IF validISBN(s) THEN
        WriteString('good');
    ELSE
        WriteString('bad');
    END;
    WriteLn;
END check;

BEGIN
    check('978-1734314502');
    check('978-1734314509');
    check('978-1788399081');
    check('978-1788399083');
END ISBN.
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

Nanoquery[edit]

Translation of: Go
def checkIsbn13(isbn)
        // remove any hyphens or spaces
        isbn = str(isbn).replace("-","").replace(" ","")

        // check length = 13
        if len(isbn) != 13
                return false
        end

        // check only contains digits and calculate weighted sum
        sum = 0
        for i in range(0, len(isbn) - 1)
                c = isbn[i]
                if (ord(c) < ord("0")) or (ord(c) > ord("9"))
                        return false
                end

                if (i % 2) = 0
                        sum += ord(c) - ord("0")
                else
                        sum += 3 * (ord(c) - ord("0"))
                end
        end

        return (sum % 10) = 0
end

isbns = {"978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"}
for isbn in isbns
        res = "bad"
        if checkIsbn13(isbn)
                res = "good"
        end

        print format("%s: %s\n", isbn, res)
end
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

Nim[edit]

import strutils, strformat

func is_isbn*(s: string): bool =
  var sum, len: int
  for c in s:
    if is_digit(c):
      sum += (ord(c) - ord('0')) * (if len mod 2 == 0: 1 else: 3)
      len += 1
    elif c != ' ' and c != '-':
      return false
  return (len == 13) and (sum mod 10 == 0)

when is_main_module:
  let isbns = [ "978-1734314502", "978-1734314509",
                "978-1788399081", "978-1788399083" ]
  for isbn in isbns:
    var quality: string = if is_isbn(isbn): "good" else: "bad"
    echo &"{isbn}: {quality}"
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

Pascal[edit]

Works with: Extended Pascal
program ISBNChecksum(output);

const
	codeIndexMaximum = 17;
	ISBNIndexMinimum = 1;
	ISBNIndexMaximum = 13;
	ISBNIndexRange = ISBNIndexMaximum - ISBNIndexMinimum + 1;

type
	code = string(codeIndexMaximum);
	codeIndex = 1..codeIndexMaximum value 1;
	decimalDigit = '0'..'9';
	decimalValue = 0..9;
	ISBNIndex = ISBNIndexMinimum..ISBNIndexMaximum;
	ISBN = array[ISBNIndex] of decimalDigit;

{ returns the integer value represented by a character }
function numericValue(protected c: decimalDigit): decimalValue;
begin
	{ in Pascal result variable bears the same name as the function }
	numericValue := ord(c) - ord('0')
end;

{ determines whether an ISBN is technically valid (checksum correct) }
function isValidISBN(protected n: ISBN): Boolean;
var
	sum: 0..225 value 0;
	i: ISBNIndex;
begin
	{ NB: in Pascal for-loop-limits are _inclusive_ }
	for i := ISBNIndexMinimum to ISBNIndexMaximum do
	begin
		{ alternating scale factor 3^0, 3^1 based on Boolean }
		sum := sum + numericValue(n[i]) * 3 pow ord(not odd(i))
	end;
	
	isValidISBN := sum mod 10 = 0
end;

{ transform '978-0-387-97649-5' into '9780387976495' }
function digits(n: code): code;
var
	sourceIndex, destinationIndex: codeIndex;
begin
	for sourceIndex := 1 to length(n) do
	begin
		if n[sourceIndex] in ['0'..'9'] then
		begin
			n[destinationIndex] := n[sourceIndex];
			destinationIndex := destinationIndex + 1
		end
	end;
	
	{ to alter a string’s length you need overwrite it completely }
	digits := subStr(n, 1, destinationIndex - 1)
end;

{ data type coercion }
function asISBN(protected n: code): ISBN;
var
	result: ISBN;
begin
	unpack(n[1..length(n)], result, 1);
	asISBN := result
end;

{ tells whether a string value contains a proper ISBN representation }
function isValidISBNString(protected hyphenatedForm: code): Boolean;
var
	digitOnlyForm: code;
begin
	digitOnlyForm := digits(hyphenatedForm);
	{ The Extended Pascal `and_then` Boolean operator allows us }
	{ to first check the length before invoking `isValidISBN`. }
	isValidISBNString := (length(digitOnlyForm) = ISBNIndexRange)
		and_then isValidISBN(asISBN(digitOnlyForm))
end;

{ === MAIN ============================================================= }
begin
	writeLn(isValidISBNString('978-1734314502'));
	writeLn(isValidISBNString('978-1734314509'));
	writeLn(isValidISBNString('978-1788399081'));
	writeLn(isValidISBNString('978-1788399083'))
end.
Output:
True
False
True
False

Perl[edit]

use strict;
use warnings;
use feature 'say';

sub check_digit {
    my($isbn) = @_; my($sum);
    $sum += (1,3)[$_%2] * (split '', join '', split /\D/, $isbn)[$_] for 0..11;
    (10 - $sum % 10) % 10;
}

for (<978-1734314502 978-1734314509 978-1788399081 978-1788399083 978-2-74839-908-0 978-2-74839-908-5>) {
    my($isbn,$check) = /(.*)(.)/;
    my $check_d = check_digit($isbn);
    say "$_ : " . ($check == $check_d ? 'Good' : "Bad check-digit $check; should be $check_d")
}
Output:
978-1734314502 : Good
978-1734314509 : Bad check-digit 9; should be 2
978-1788399081 : Good
978-1788399083 : Bad check-digit 3; should be 1
978-2-74839-908-0 : Good
978-2-74839-908-5 : Bad check-digit 5; should be 0

Phix[edit]

with javascript_semantics
procedure check_isbn13(string isbn)
    integer digits = 0, checksum = 0, w = 1
    for i=1 to length(isbn) do
        integer ch = isbn[i]
        if ch!=' ' and ch!='-' then
            ch -= '0'
            if ch<0 or ch>9 then checksum = 9 exit end if
            checksum += ch*w
            digits += 1
            w = 4-w
        end if
    end for
    checksum = remainder(checksum,10)
    string gb = iff(digits=13 and checksum=0 ? "good" : "bad")
    printf(1,"%s: %s\n",{isbn,gb})
end procedure
 
constant isbns = {"978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083",
                  "978-2-74839-908-0","978-2-74839-908-5","978 1 86197 876 9"}
for i=1 to length(isbns) do check_isbn13(isbns[i]) end for
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad
978-2-74839-908-0: good
978-2-74839-908-5: bad
978 1 86197 876 9: good

PicoLisp[edit]

(de isbn13? (S)
   (let L
      (make
         (for N (chop S)
            (and (format N) (link @)) ) )
      (and
         (= 13 (length L))
         (=0 (% (sum * L (circ 1 3)) 10)) ) ) )
(mapc
   '((A)
      (tab
         (-19 1)
         A
         (if (isbn13? A) 'ok 'fail) ) )
   (quote
      "978-1734314502"
      "978-1734314509"
      "978-1-86197-876-9"
      "978-2-74839-908-5"
      "978 1 86197 876 9" ) )
Output:
978-1734314502     ok
978-1734314509     fail
978-1-86197-876-9  ok
978-2-74839-908-5  fail
978 1 86197 876 9  ok

PL/M[edit]

100H:

CHECK$ISBN13: PROCEDURE (PTR) BYTE;
    DECLARE PTR ADDRESS, ISBN BASED PTR BYTE;
    DECLARE (I, F, T) BYTE;
    F = 1;
    T = 0;
    DO I = 0 TO 13;
        IF I = 3 THEN DO;
            /* THIRD CHAR SHOULD BE '-' */
            IF ISBN(I) <> '-' THEN RETURN 0;
        END;
        ELSE DO;
            /* DIGITS MUST BE VALID */
            IF ISBN(I) < '0' OR ISBN(I) > '9' THEN RETURN 0;
            T = T + (ISBN(I) - '0') * F;
            F = 4 - F; /* MULTIPLY BY 1 AND 3 ALTERNATELY */
        END;
    END;
    RETURN (T MOD 10) = 0;
END CHECK$ISBN13;

/* CP/M BDOS CALL */
BDOS: PROCEDURE (FUNC, ARG);
    DECLARE FUNC BYTE, ARG ADDRESS;
    GO TO 5;
END BDOS;

PRINT: PROCEDURE (STR);
    DECLARE STR ADDRESS;
    CALL BDOS(9, STR);
END PRINT;

/* TESTS */
DECLARE TEST (4) ADDRESS;
TEST(0) = .'978-1734314502$';
TEST(1) = .'978-1734314509$';
TEST(2) = .'978-1788399081$';
TEST(3) = .'978-1788399083$';

DECLARE I BYTE;
DO I = 0 TO LAST(TEST);
    CALL PRINT(TEST(I));
    CALL PRINT(.': $');
    IF CHECK$ISBN13(TEST(I)) THEN
        CALL PRINT(.'GOOD$');
    ELSE
        CALL PRINT(.'BAD$');
    CALL PRINT(.(13,10,'$'));
END;

CALL BDOS(0,0);
EOF
Output:
978-1734314502: GOOD
978-1734314509: BAD
978-1788399081: GOOD
978-1788399083: BAD

PowerShell[edit]

function Get-ISBN13 {
    $codes = (
        "978-1734314502",
        "978-1734314509",
        "978-1788399081",
        "978-1788399083"
    )

    foreach ($line in $codes) {

        $sum = $null
        $codeNoDash = $line.Replace("-","")

        for ($i = 0; $i -lt $codeNoDash.length; $i++) {

            if (($i % 2) -eq 1) {

                $sum += [decimal]$codeNoDash[$i] * 3
               
            }else {

                $sum += [decimal]$codeNoDash[$i]

            }
        }
        
        if (($sum % 10) -eq 0) {

            Write-Host "$line Good"
            
        }else {

            Write-Host "$line Bad"

        }
    }
}
Get-ISBN13
Output:
978-1734314502 Good
978-1734314509 Bad
978-1788399081 Good
978-1788399083 Bad

PureBasic[edit]

Macro TestISBN13(X)  
  Print(X) 
  If IsISBN13(X) : PrintN(" good") : Else : PrintN(" bad") : EndIf  
EndMacro

Procedure.b IsISBN13(ISBN13.s)  
  ISBN13=Left(ISBN13,3)+Mid(ISBN13,5)  
  If IsNAN(Val(ISBN13)) Or Len(ISBN13)<>13 : ProcedureReturn #False : EndIf
  Dim ISBN.s{1}(12) : PokeS(@ISBN(),ISBN13)  
  For i=0 To 11 Step 2 : sum+Val(ISBN(i))+Val(ISBN(i+1))*3 : Next
  sum+Val(ISBN(12))
  ProcedureReturn Bool(sum%10=0)
EndProcedure

If OpenConsole()
  TestISBN13("978-1734314502")
  TestISBN13("978-1734314509")
  TestISBN13("978-1788399081")
  TestISBN13("978-1788399083")
  Input()
EndIf
Output:
978-1734314502 good
978-1734314509 bad
978-1788399081 good
978-1788399083 bad

Python[edit]

def is_isbn13(n):
    n = n.replace('-','').replace(' ', '')
    if len(n) != 13:
        return False
    product = (sum(int(ch) for ch in n[::2]) 
               + sum(int(ch) * 3 for ch in n[1::2]))
    return product % 10 == 0

if __name__ == '__main__':
    tests = '''
978-1734314502
978-1734314509
978-1788399081
978-1788399083'''.strip().split()
    for t in tests:
        print(f"ISBN13 {t} validates {is_isbn13(t)}")
Output:
ISBN13 978-1734314502 validates True
ISBN13 978-1734314509 validates False
ISBN13 978-1788399081 validates True
ISBN13 978-1788399083 validates False


Or, expressed in terms of itertools.cycle

'''ISBN13 check digit'''


from itertools import cycle


# isISBN13 :: String -> Bool
def isISBN13(s):
    '''True if s is a valid ISBN13 string
    '''
    digits = [int(c) for c in s if c.isdigit()]
    return 13 == len(digits) and (
        0 == sum(map(
            lambda f, x: f(x),
            cycle([
                lambda x: x,
                lambda x: 3 * x
            ]),
            digits
        )) % 10
    )


# ------------------------- TEST -------------------------
# main :: IO ()
def main():
    '''Test strings for ISBN-13 validity.'''

    print('\n'.join(
        repr((s, isISBN13(s))) for s
        in ["978-1734314502",
            "978-1734314509",
            "978-1788399081",
            "978-1788399083"
            ]
    ))


# MAIN ---
if __name__ == '__main__':
    main()
Output:
('978-1734314502', True)
('978-1734314509', False)
('978-1788399081', True)
('978-1788399083', False)

Quackery[edit]

[ char 0 char 9 1+ within ]  is digit?    ( c --> b )

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

[ [] swap ]'[ swap
  witheach [ 
    dup nested 
    unrot over do
    iff [ dip join ]
    else nip
  ] drop ]                   is filter    ( [ --> [ )

[ 0 swap
  witheach [
    char->n i^ odd?
    iff [ 3 * + ]
    else +
  ] ]                        is checksum  ( $ --> n )

[ filter digit?
  dup size 13 = not
  iff [ drop false ] done
  checksum 10 mod 0 = ]      is isbn      ( $ --> b )

[ dup echo$ say ": " isbn
  iff [ say "Good" ]
  else [ say "Bad" ] cr ]    is isbn-test ( $ -->   )

$ '978-1734314502' isbn-test
$ '978-1734314509' isbn-test
$ '978-1788399081' isbn-test
$ '978-1788399083' isbn-test
Output:
978-1734314502: Good
978-1734314509: Bad
978-1788399081: Good
978-1788399083: Bad

Racket[edit]

#lang racket/base

(define (isbn13-check-digit-valid? s)
  (zero? (modulo (for/sum ((i (in-naturals))
                           (d (regexp-replace* #px"[^[:digit:]]" s "")))
                   (* (- (char->integer d) (char->integer #\0))
                      (if (even? i) 1 3)))
                 10)))

(module+ test
  (require rackunit)
  (check-true (isbn13-check-digit-valid? "978-1734314502"))
  (check-false (isbn13-check-digit-valid? "978-1734314509"))
  (check-true (isbn13-check-digit-valid? "978-1788399081"))
  (check-false (isbn13-check-digit-valid? "978-1788399083")))
Output:

no output indicates tests pass

Raku[edit]

(formerly Perl 6)

Works with: Rakudo version 2019.11

Also test a value that has a zero check digit.

sub check-digit ($isbn) {
     (10 - (sum (|$isbn.comb(/<[0..9]>/)) »*» (1,3)) % 10).substr: *-1
}

{
    my $check = .substr(*-1);
    my $check-digit = check-digit .chop;
    say "$_ : ", $check == $check-digit ??
        'Good' !!
        "Bad check-digit $check; should be $check-digit"
} for words <
    978-1734314502
    978-1734314509
    978-1788399081
    978-1788399083
    978-2-74839-908-0
    978-2-74839-908-5
>;
Output:
978-1734314502 : Good
978-1734314509 : Bad check-digit 9; should be 2
978-1788399081 : Good
978-1788399083 : Bad check-digit 3; should be 1
978-2-74839-908-0 : Good
978-2-74839-908-5 : Bad check-digit 5; should be 0

Red[edit]

check_valid_isbn13: function [str] [
  is_digit: charset [#"0" - #"9"]
  remove-each i str [not pick is_digit i] ; remove non-digits

  either 13 = length? str [               ; reject strings of incorrect length
    sum: 0
    repeat i 13 [
      mul: either even? i [3] [1]         ; multiplier for odd/even digits
      sum: sum + (mul * to integer! to string! pick str i)
    ]
    
    zero? (sum % 10)                      ; check if remainder mod 10 is zero
  ] [
    false
  ]
]

; check given examples
foreach [str] ["978-1734314502" "978-1734314509" "978-1788399081" "978-1788399083"] [
  prin str
  prin " - "
  print check_valid_isbn13 str
]
Output:
978-1734314502 - true
978-1734314509 - false
978-1788399081 - true
978-1788399083 - false

REXX[edit]

A couple of additional checks were made to verify a correct length,   and also that the ISBN-13 code is all numerics   (with optional minus signs).

/*REXX pgm validates the check digit of an ISBN─13 code  (it may have embedded minuses).*/
parse arg $                                      /*obtain optional arguments from the CL*/
if $='' | if $=","  then $= '978-1734314502 978-1734314509 978-1788399081 978-1788399083'
@ISBN= "ISBN─13 code isn't"                      /*a literal used when displaying msgs. */
                                                 /* [↓]  remove all minuses from X code.*/
  do j=1  for words($);  y= word($,j)            /*obtain an ISBN─13 code from  $  list.*/
  x= space( translate(y, , '-'),  0)             /*remove all minus signs from the code.*/
  L= length(x)                                   /*obtain the length of the ISBN-13 code*/
  if L \== 13                   then do;  say @ISBN  '13 characters: '  x;  exit 13;   end
  if verify(x, 9876543210)\==0  then do;  say @ISBN  'numeric: '        x;  exit 10;   end
  sum= 0
          do k=1  for L;   #= substr(x, k, 1)    /*get a decimal digit from the X code. */
          if \(k//2)  then #= # * 3              /*multiply every other digit by three. */
          sum= sum + #                           /*add the digit (or product) to the SUM*/
          end   /*k*/

  if right(sum, 1)==0  then say '     ISBN-13 code '      x      "    is valid."
                       else say '     ISBN-13 code '      x      " isn't valid."
  end   /*j*/                                    /*stick a fork in it,  we're all done. */
output   when using the four default inputs:
     ISBN-13 code  9781734314502     is valid.
     ISBN-13 code  9781734314509  isn't valid.
     ISBN-13 code  9781788399081     is valid.
     ISBN-13 code  9781788399083  isn't valid.

Ring[edit]

load "stdlib.ring"

isbn = ["978-1734314502","978-1734314509", "978-1788399081", "978-1788399083","978-2-74839-908-0","978-2-74839-908-5","978 1 86197 876 9"]

for n = 1 to len(isbn)
    sum = 0
    isbnStr = isbn[n]
    isbnStr = substr(isbnStr,"-","")
    isbnStr = substr(isbnStr," ","")
    for m = 1 to len(isbnStr)
        if m%2 = 0
           num = 3*number(substr(isbnStr,m,1))
           sum = sum + num
        else
           num = number(substr(isbnStr,m,1))
           sum = sum + num
        ok
    next
    if sum%10 = 0
       see "" + isbn[n] + ": true" + nl
    else
       see "" + isbn[n] + ": bad" + nl
    ok
next

Output:

978-1734314502: true
978-1734314509: bad
978-1788399081: true
978-1788399083: bad
978-2-74839-908-0: true
978-2-74839-908-5: bad
978 1 86197 876 9: true

Ruby[edit]

def validISBN13?(str)
  cleaned = str.delete("^0-9").chars
  return false unless cleaned.size == 13
  cleaned.each_slice(2).sum{|d1, d2| d1.to_i + 3*d2.to_i }.remainder(10) == 0
end

isbns = ["978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"]
isbns.each{|isbn| puts "#{isbn}: #{validISBN13?(isbn)}" }
Output:
978-1734314502: true
978-1734314509: false
978-1788399081: true
978-1788399083: false

Rust[edit]

fn main() {
    let isbns = ["978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"];
    isbns.iter().for_each(|isbn| println!("{}: {}", isbn, check_isbn(isbn)));
}

fn check_isbn(isbn: &str) -> bool {
    if isbn.chars().filter(|c| c.is_digit(10)).count() != 13 {
            return false;
    } 
    let checksum = isbn.chars().filter_map(|c| c.to_digit(10))
        .zip([1, 3].iter().cycle())
        .fold(0, |acc, (val, fac)| acc + val * fac);
    checksum % 10 == 0
}
Output:
978-1734314502: true
978-1734314509: false
978-1788399081: true
978-1788399083: false

Seed7[edit]

$ include "seed7_05.s7i";

const func boolean: isISBN13 (in var string: input) is func
  result
    var boolean: isbn is FALSE;
  local
    var char: c is ' ';
    var integer: digit is 0;
    var integer: i is 1;
    var integer: sum is 0;
  begin
    input := replace(input, " ", "");
    input := replace(input, "-", "");
    if length(input) = 13 then
      for c range input do
        digit := ord(c) - 48;
        if not odd(i) then
          digit *:= 3;
        end if;
        sum +:= digit;
        incr(i);
      end for;
      isbn := sum rem 10 = 0;
    end if;
  end func;

const proc: main is func
  local
    var string: str is "";
  begin
    for str range [] ("978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083") do
      writeln(str <& ": " <& isISBN13(str));
    end for;
  end func;
Output:
978-1734314502: TRUE
978-1734314509: FALSE
978-1788399081: TRUE
978-1788399083: FALSE

Standard ML[edit]

local
  fun check (c, p as (m, n)) =
    if Char.isDigit c then
      (not m, (if m then 3 * (ord c - 48) else ord c - 48) + n)
    else
      p
in
  fun checkISBN s =
    Int.rem (#2 (CharVector.foldl check (false, 0) s), 10) = 0
end

val test = ["978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"]
val () = (print
          o concat
          o map (fn s => s ^ (if checkISBN s then ": good\n" else ": bad\n"))) test
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

Swift[edit]

func checkISBN(isbn: String) -> Bool {
  guard !isbn.isEmpty else {
    return false
  }

  let sum = isbn
    .compactMap({ $0.wholeNumberValue })
    .enumerated()
    .map({ $0.offset & 1 == 1 ? 3 * $0.element : $0.element })
    .reduce(0, +)

  return sum % 10 == 0
}

let cases = [
  "978-1734314502",
  "978-1734314509",
  "978-1788399081",
  "978-1788399083"
]

for isbn in cases {
  print("\(isbn) => \(checkISBN(isbn: isbn) ? "good" : "bad")")
}


Output:
978-1734314502 => good
978-1734314509 => bad
978-1788399081 => good
978-1788399083 => bad

Tcl[edit]

proc validISBN13 code {
   regsub -all {\D} $code "" code ;# remove non-digits
   if {[string length $code] == 13} {
      set sum 0
      set fac 1
      foreach digit [split $code ""] {
         set sum [expr {$sum + $digit * $fac}]
         set fac [expr {$fac == 1? 3: 1}]
      }
      if {$sum % 10 == 0} {return true}
   }
   return false
}
foreach test {
   978-1734314502
   978-1734314509
   978-1788399081
   978-1788399083
} {puts $test:[validISBN13 $test]}
Output:
978-1734314502:true
978-1734314509:false
978-1788399081:true
978-1788399083:false

Simpler variant, using two loop vars and constant factors; same output:

proc validISBN13 code {
   regsub -all {\D} $code "" code ;# remove non-digits
   if {[string length $code] == 13} {
      set sum 0
      foreach {d1 d2} [split $code ""] {
         if {$d2 eq ""} {set d2 0} ;# last round
         set sum [expr {$sum + $d1 + $d2 * 3}]
      }
      if {$sum % 10 == 0} {return true}
   }
   return false
}

uBasic/4tH[edit]

Works with: version 3.64.0
a := "978-1734314502" 
Print Show(a), Show (Iif (Func(_IsISBN (a)), "good", "bad"))

a := "978-1734314509"
Print Show(a), Show (Iif (Func(_IsISBN (a)), "good", "bad"))

a := "978-1788399081"
Print Show(a), Show (Iif (Func(_IsISBN (a)), "good", "bad"))

a := "978-1788399083"
Print Show(a), Show (Iif (Func(_IsISBN (a)), "good", "bad"))

End

_IsISBN
  Param (1)
  Local (4)

  c@ = 0 : e@ = 1                      ' set sum and multiplier

  For b@ = Len (a@) - 1 To 0 Step -1   ' scan string in reverse
    d@ = Peek(a@, b@) - Ord ("0")      ' get character
    If ((d@ < 0) + (d@ > 9)) = 0 Then c@ = c@ + (d@ * e@)
    e@ = (e@ * 3) % 8                  ' evaluate character, change multiplier
  Next

Return ((c@ % 10) = 0)                 ' modulus 10 must be zero
Output:
978-1734314502  good
978-1734314509  bad
978-1788399081  good
978-1788399083  bad

0 OK, 0:339

UNIX Shell[edit]

Works with: Bourne Again Shell
check_isbn13 () {
    local i n t
    n=${1//[^0-9]/}
    t=0
    for ((i=0; i<${#n}; ++i )); do
      (( t += ${n:i:1}*(1 + ((i&1)<<1)) ))
    done
    (( 0 == t % 10 ))
}

for isbn in 978-1734314502 978-1734314509 978-1788399081 978-1788399083; do
  printf '%s: ' "$isbn"
  if check_isbn13 "$isbn"; then
    printf '%s\n' OK
  else
    printf '%s\n' 'NOT OK'
  fi
done
Output:
978-1734314502: OK
978-1734314509: NOT OK
978-1788399081: OK
978-1788399083: NOT OK

Visual Basic .NET[edit]

Translation of: C#
Module Module1

    Function CheckISBN13(code As String) As Boolean
        code = code.Replace("-", "").Replace(" ", "")
        If code.Length <> 13 Then
            Return False
        End If
        Dim sum = 0
        For Each i_d In code.Select(Function(digit, index) (index, digit))
            Dim index = i_d.index
            Dim digit = i_d.digit
            If Char.IsDigit(digit) Then
                sum += (Asc(digit) - Asc("0")) * If(index Mod 2 = 0, 1, 3)
            Else
                Return False
            End If
        Next
        Return sum Mod 10 = 0
    End Function

    Sub Main()
        Console.WriteLine(CheckISBN13("978-1734314502"))
        Console.WriteLine(CheckISBN13("978-1734314509"))
        Console.WriteLine(CheckISBN13("978-1788399081"))
        Console.WriteLine(CheckISBN13("978-1788399083"))
    End Sub

End Module
Output:
True
False
True
False

Vlang[edit]

Translation of: Go
fn check_isbn13(isbn13 string) bool {
    // remove any hyphens or spaces
    isbn := isbn13.replace('-','').replace(' ','')
    // check length == 13
    le := isbn.len
    if le != 13 {
        return false
    }
    // check only contains digits and calculate weighted sum
    mut sum := 0
    for i, c in isbn.split('') {
        if c.int() < '0'.int() || c.int() > '9'.int() {
            return false
        }
        if i%2 == 0 {
            sum += c.int() - '0'.int()
        } else {
            sum += 3 * (c.int() - '0'.int())
        }
    }
    return sum%10 == 0
}
 
fn main() {
    isbns := ["978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"]
    for isbn in isbns {
        mut res := "bad"
        if check_isbn13(isbn) {
            res = "good"
        }
        println("$isbn: $res")
    }
}
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad

Wren[edit]

var isbn13 = Fn.new { |s|
    var cps = s.codePoints
    var digits = []
    // extract digits
    for (i in 0...cps.count) {
        var c = cps[i]
        if (c >= 48 && c <= 57) digits.add(c)
    }
    // do calcs
    var sum = 0
    for (i in 0...digits.count) {
        var d = digits[i] - 48
        sum = sum + ((i%2 == 0) ? d : 3 * d)
    }
    return sum % 10 == 0
}

var tests = ["978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"]
for (test in tests) {
    System.print("%(test) -> %(isbn13.call(test) ? "good" : "bad")")
}
Output:
978-1734314502 -> good
978-1734314509 -> bad
978-1788399081 -> good
978-1788399083 -> bad

XPL0[edit]

include xpllib;         \contains StrLen function

proc ISBN13(Str);       \Show if International Standard Book Number is good
char Str;
int Sum, Cnt, Dig, I;
[Sum:= 0;  Cnt:= 0;
for I:= 0 to StrLen(Str)-1 do
    [Dig:= Str(I) - ^0;
    if Dig>=0 & Dig<=9 then
        [Sum:= Sum + Dig;
         Cnt:= Cnt + 1;
         if (Cnt&1) = 0 then
                Sum:= Sum + Dig + Dig;
        ];
    ];
Text(0, Str);
Text(0, if rem(Sum/10)=0 & Cnt=13 then ": good" else ": bad");
CrLf(0);
];

[ISBN13("978-1734314502");
 ISBN13("978-1734314509");
 ISBN13("978-1788399081");
 ISBN13("978-1788399083");
 ISBN13("978-1-59327-220-3");
 ISBN13("978-178839918");
]
Output:
978-1734314502: good
978-1734314509: bad
978-1788399081: good
978-1788399083: bad
978-1-59327-220-3: good
978-178839918: bad

zkl[edit]

fcn ISBN13_check(isbn){  // "978-1734314502", throws on invalid digits
   var [const] one3=("13"*6 + 1).split("").apply("toInt"); // examine 13 digits
   // one3=("13"*6) if you want to calculate what the check digit should be
   one3.zipWith('*,isbn - " -").sum(0) % 10 == 0
}
isbns:=
#<<<"
    978-1734314502
    978-1734314509
    978-1788399081
    978-1788399083
    978-2-74839-908-0
    978-2-74839-908-5".split("\n");
#<<<
foreach isbn in (isbns)
   { println(isbn.strip(),"  ",ISBN13_check(isbn) and " Good" or " Bad") }
Output:
978-1734314502   Good
978-1734314509   Bad
978-1788399081   Good
978-1788399083   Bad
978-2-74839-908-0   Good
978-2-74839-908-5   Bad