How to add all digits of a number in C

main.c

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

int sumOfDigits(int n) {
    int sum = 0;
    while (n > 0) {
        int d = n % 10;
        n = n / 10;
        sum += d;
    }
}

int main(int argc, char* argv[]) {
    int x = 38511;
    printf("Sum of the digits of %d is %d\n", x, sumOfDigits(x));
    return 0;
}