sum of product using modulaar arithmetic

#include <stdio.h>
int main()
{
    long long x; // as x <= 10^19
    scanf("%lld", &x);

    long long q = x, r, sum = 0;

    while(q > 0) {
        r = q % 10;
        sum += r;
        q /= 10;
    }

    printf("%lld\n", sum);


    return 0;
}