strong number

#include <stdio.h>
#include <stdbool.h>

/* fac(n) : factorial of n. n >= 0 */
int fac(int n) {
    int p = 1;
    for (; n > 0; n--)
        p *= n;
    return p;
}

/* strnum(n) : test strong number of n */
bool strnum(int n) {
    int diff;
    for (diff = n; n/10 != 0; n /= 10)
        diff -= fac(n%10);
    diff -= fac(n);
    return (diff == 0);
}

int main() {
    int n;

    printf("find strong number up to ");
    scanf("%d", &n);
    for (int i = 0; i <= n; i++)
        if (strnum(i)) printf("%d is a strong number\n", i);

    return 0;
}