ACM 10922 2 the 9s

#include <stdio.h>
#include <string.h>

int main(void)
{
    char s[1001];
    int len, sum, temp, degree;

    while (gets(s) != NULL
           && !(s[0] == '0' && s[1] == '\0')) {
        len = strlen(s);
        sum = 0;
        while (len > 0)
            sum += s[--len] - '0';
        if (sum % 9 != 0) {
            printf("%s is not a multiple of 9.\n", s);
            continue;
        }

        degree = 1;
        while (sum != 9) {
            temp = sum;
            sum = 0;
            while (temp != 0) {
                sum += temp % 10;
                temp /= 10;
            }
            degree++;
        }
        printf("%s is a multiple of 9 and has 9-degree %d.\n", s, degree);
    }

    return 0;
}