Program involving matrices and functions

Question

I’m having trouble with this code.

I have to read from the 9 digits of isbn and generate the scanner code, this is ok.

But I have to do a repeat where the program only closes when the user type 000000000 and I’m not able to find a way, I tried so but it didn’t work:

#include <stdio.h>

char isbn_dv(char isbn[9])
{
 while (isbn[9]!=000000000){
 int s1 = 0;
 int s2 = 0;
 for (int i = 0; i < 9; i++)
     s1 += isbn[i] - '0', s2 += s1;
 int digito = 11 - ((s1+s2) % 11);
 if (digito == 11) return '0';
 if (digito == 10) return 'X';
 return '0' + digito;
 }
}

int main(void){
 char isbn[9];
 
 scanf("%9s", isbn);
 printf("%s-%c", isbn, isbn_dv(isbn));
 
 return 0;
}