array addition

#include <stdio.h>
void print_array(int a[], int num_elements) {
    int i;
    for (i=0; i<num_elements; i++)
    {
        printf("%d ", a[i]);
    }
printf("\n");
}

int main(){
    int a1[4] = { 1, 2, 3, 4};
    int a1_length = 4;
    int a2[3] = { 1, 2, 3};
    int a2_length = 3;
    int answer[4];
    int sum = 0;
    int val = 0;
    int i;
    for (i=0; i < a1_length; i++) {
        printf("i: %d\n", i);
        if (i >= a2_length) {
            val = 0;
        }
        else {
            val = a2[i];
        }
        answer[i] = val + a1[i];
        printf("%d + %d + %d\n", sum, a1[i], val);
        sum = sum + a1[i] + val;
    }
printf("sum: %d\n", sum);
print_array(answer, 4);
return 0;
}