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 the digits together.
- Take the remainder of division by 10.
- If it is 0, the ISBN-13 check digit is correct.
Use the following codes for testing:
- 978-1734314502 (good)
- 978-1734314509 (bad)
- 978-1788399081 (good)
- 978-1788399083 (bad)
Show output here, on this page
- See also
-
- for details: 13-digit ISBN method of validation. (Uses cookies.)
8080 Assembly
<lang 8080asm> 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$' bad: db 'bad$'</lang>
- Output:
A>isbn13 978-1734314502 good A>isbn13 978-1734314509 bad A>isbn13 978-1788399081 good A>isbn13 978-1788399083 bad
8086 Assembly
<lang asm> 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$' bad: db 'bad$'</lang>
- Output:
C:\>isbn13 978-1734314502 good C:\>isbn13 978-1734314509 bad C:\>isbn13 978-1788399081 good C:\>isbn13 978-1788399083 bad
ALGOL 68
<lang algol68>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</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad
AppleScript
Composition of pure functions
<lang applescript>-------------------- 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</lang>
- Output:
{{"978-1734314502", true}, {"978-1734314509", false}, {"978-1788399081", true}, {"978-1788399083", false}}
Straightforward
This task can be tackled very simply by working through the numeric text two characters at a time:
<lang applescript>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</lang>
- 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).
<lang applescript>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</lang>
AutoHotkey
<lang AutoHotkey>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)") }</lang> Examples:<lang AutoHotkey>output := "" nums := ["978-1734314502","978-1734314509","978-1788399081","978-1788399083"] for i, n in nums output .= ISBN13_check_digit(n) "`n" MsgBox % output return</lang>
- Output:
978-1734314502 (good) 978-1734314509 (bad) 978-1788399081 (good) 978-1788399083 (bad)
AWK
<lang AWK>
- 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))
} </lang>
- 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
C
<lang c>#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;
}</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad
C++
<lang cpp>#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;
}</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad
C#
<lang csharp>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;
}
}
}</lang>
- Output:
True False True False
D
<lang d>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"));
}</lang>
Factor
<lang factor>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</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad
FreeBASIC
<lang freebasic>#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</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad
Go
<lang go>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)
}
}</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad
Haskell
<lang haskell>import Data.Char (isDigit, digitToInt) import Control.Monad (forM_) import Text.Printf (printf)
testISBNs :: [String] testISBNs = ["978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"]
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 = forM_ testISBNs (\isbn -> printf "%s: Valid: %s\n" isbn (show $ validIsbn13 isbn))</lang>
- Output:
978-1734314502: Valid: True 978-1734314509: Valid: False 978-1788399081: Valid: True 978-1788399083: Valid: False
Or, expressed in terms of cycle:
<lang haskell>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) <$> ["978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"]</lang>
- Output:
("978-1734314502",True)
("978-1734314509",False)
("978-1788399081",True)
("978-1788399083",False)
IS-BASIC
<lang IS-BASIC>100 PROGRAM "ISBN13.bas" 110 DO 120 PRINT :INPUT PROMPT "ISBN-13 code: ":IS$ 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</lang>
Julia
<lang julia>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
</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad
Kotlin
<lang Kotlin> 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
} </lang>
Tested using Spek <lang Kotlin> 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: ${when(isValidISBN13(input)) {
true -> "good"
else -> "bad"
}}")
assert(isValidISBN13(input) == expected)
}
}
} </lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad
langur
In this example, we map to multiple functions (actually 1 no-op). <lang langur>val .isbn13checkdigit = f(var .s) {
.s = replace(.s, RE/[\- ]/)
matching(re/^[0-9]{13}$/, .s) and
fold(f{+}, map [_, f{x 3}], s2n .s) div 10
}
val .tests = h{
"978-1734314502": true, "978-1734314509": 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)")
}</lang>
In this example, we set a for loop value as it progresses. <lang langur>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{
"978-1734314502": true, "978-1734314509": 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)")
}</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad
Lua
<lang lua>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()</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad
Nanoquery
<lang nanoquery>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</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad
Nim
<lang nim>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}"</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad
Perl
<lang perl>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")
}</lang>
- 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
<lang Phix>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</lang>
- 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
<lang PicoLisp>(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" ) )</lang>
- 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
Python
<lang python>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)}")</lang>
- 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
<lang python>ISBN13 check digit
from itertools import cycle from operator import mul
- isISBN13 :: String -> Bool
def isISBN13(s):
True if the digits of s form
a valid ISBN-13 code.
digits = [int(c) for c in s if c.isdigit()]
return 13 == len(digits) and 0 == sum(
map(
mul,
digits,
cycle([1, 3])
)
) % 10
- ---------------------------TEST---------------------------
- main :: IO ()
def main():
Validation of four strings:
for s in ['978-1734314502', '978-1734314509',
'978-1788399081', '978-1788399083']:
print((s, isISBN13(s)))
- MAIN ---
if __name__ == '__main__':
main()</lang>
- Output:
('978-1734314502', True)
('978-1734314509', False)
('978-1788399081', True)
('978-1788399083', False)
Racket
<lang racket>#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")))</lang>
- Output:
no output indicates tests pass
Raku
(formerly Perl 6)
Also test a value that has a zero check digit.
<lang perl6>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
>;</lang>
- 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
REXX
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). <lang rexx>/*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. */</lang>
- 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.
Ruby
<lang ruby>def checkISBN13(code)
length = 0 sum = 0
code.split().each { |c|
if '0' <= c and c <= '9' then
if length % 2 == 0 then
sum = sum + 1 * (c.ord - '0'.ord)
else
sum = sum + 3 * (c.ord - '0'.ord)
end
length = length + 1
end
}
if length != 13 then
return false
end
return sum % 10 == 0
end
def main
puts checkISBN13("978-1734314502")
puts checkISBN13("978-1734314509")
puts checkISBN13("978-1788399081")
puts checkISBN13("978-1788399083")
end
main()</lang>
- Output:
true false true false
Rust
<lang rust>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
} </lang>
- Output:
978-1734314502: true 978-1734314509: false 978-1788399081: true 978-1788399083: false
Swift
<lang swift>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")")
}</lang>
- Output:
978-1734314502 => good 978-1734314509 => bad 978-1788399081 => good 978-1788399083 => bad
Wren
<lang ecmascript>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")")
}</lang>
- Output:
978-1734314502 -> good 978-1734314509 -> bad 978-1788399081 -> good 978-1788399083 -> bad
XPL0
<lang XPL0>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");
]</lang>
- Output:
978-1734314502: good 978-1734314509: bad 978-1788399081: good 978-1788399083: bad 978-1-59327-220-3: good 978-178839918: bad
zkl
<lang zkl>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
}</lang> <lang zkl>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") }</lang>
- 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