ISBN13 check digit
- 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
See https://isbn-information.com/the-13-digit-isbn.html for details on the method of validation.
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
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
langur
<lang langur>val .isbn13checkdigit = f(.n) {
val .s = replace(.n, RE/[\- ]/, ZLS)
if len(.s) != 13 {
return false
}
# multiply every other number by 3
val .nums = map(
f(.i, .d) if(.i rem 2 == 0: .d x 3; .d),
series(13),
map f .c-'0', s2cp .s,
)
fold(f .x + .y, .nums) rem 10 == 0
}
val .tests = h{
"978-1734314502": true, "978-1734314509": false, "978-1788399081": true, "978-1788399083": false,
}
for .key in sort(keys .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
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 $check_d")
}</lang>
- Output:
978-1734314502 : Good 978-1734314509 : Bad check-digit 9; should be 2 978-1788399081 : Good 978-1788399083 : Bad check-digit 3; should be 1 978-2-74839-908-0 : Good 978-2-74839-908-5 : Bad check-digit 5; should be 0
Perl 6
Also test a value that has a zero check digit.
<lang perl6>sub check-digit ($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
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
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.