Average of the digits (string)

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

int main()
{
    char num[25];
    scanf("%s", num);

    int q, r, sum = 0;
    int len = strlen(num);
    int i;

    for(i = 0; i < len; i++) {
        sum += num[i] - '0';
    }
    double avg = (double)sum / (double)(strlen(num));

    printf("%lf\n", avg);


    return 0;
}