Re: program to verify ISBN numbers (10 digit or 13 digit)

? (3+X)%10
%1 = 0

Bernadette

> Le 31 janv. 2025 à 18:59, Bill Allombert <[email protected]> a écrit :
> 
> On Fri, Jan 31, 2025 at 02:08:24AM +0100, Karim Belabas wrote:
>> Here's a further shortened version.
> 
> verify_isbn(N)=
> { my(M, n, z);
>  M = Map([10, [[10,9,8,7,6,5,4,3,2,1]~, 11];
>           13, [[1,3,1,3,1,3,1,3,1,3,1,3,1]~, 10]]);
>  n = if (type(N)=="t_STR", apply(eval, select(c -> c != "-", Vec(N))),
>          type(N)=="t_INT", digits(N));
>  if (!mapisdefined(M, #n, &z) || (n * z[1]) % z[2], print("Invalid! ", N)
>                                                   , print("Valid ISBN: ", N));
> }
> 
> 2 comments: 
> - for the '13' case, this just check this is an EAN13. To be an ISBN
> it needs to start by 978 or 979.
> 
> - for the '10' case, the last digit can be the letter X to denote 10,
> since the checksum is mod 11.
> 
> Game: why do we get this:
> ? verify_isbn("0-0000-0001-X");
> Valid ISBN: 0-0000-0001-X
> 
> Cheers,
> Bill, small-scale book publisher.
>