/*
** ISISBN.C - Validate International Standard Book Numbers (ISBNs)
**
** public domain by Maynard Hogg
*/
#include <ctype.h>
int isbn2(char *str)
{
int i = 0;
int test = 0;
int c;
while ('\0' != (c = *str++))
{
if (isdigit(c))
c -= '0';
else if (i == 9 && 'X' == c)
c = 10;
else continue;
test += c * ++i;
}
return (i == 10 && test % 11 == 0);
}