Thread: Question regarding a function

Hey,
I have stumbled upon an issue.
I've attached my code below.

I am writing a function of long numbers, and it works, it sums up the numbers.

I need it to multiply the numbers instead, and when I do it, it gives me a wrong answer...
Can you guys maybe check the code and review it for me?

Code:

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

typedef char* verylong;
verylong add_verylong(verylong vl1, verylong vl2);


int main() {
    verylong result = add_verylong("99", "888");
    for (int i = 0; i < sizeof(result); i++) {
        printf("%c", result[i]);
    }
    return 0;
}
verylong add_verylong(verylong vl1, verylong vl2) {
    int len_1 = strlen(vl1);
    int len_2 = strlen(vl2);
    int vl1_number = 0;
    int vl2_number = 0;
    int mul = 1;
    while (len_1 > 0) {
        int x = vl1[len_1 - 1] - '0';
        x = x * mul;
        vl1_number = vl1_number + x;
        mul *= 10;
        len_1--;
    }
    mul = 1;
    while (len_2 > 0) {
        int x = vl2[len_2 - 1] - '0';
        x = x * mul;
        vl2_number += x;
        mul = mul * 10;
        len_2--;
    }
    int number = vl1_number + vl2_number;
    int length = 0;
    int temp = number;
    while (temp > 0) {
        length += 1;
        temp /= 10;
    }


    verylong result = (char*)calloc(length + 1, sizeof(char));
    result[length--] = '\0';
    while (number > 0) {
        int x = number % 10;
        char c = x + '0';
        result[length--] = c;
        number /= 10;
    }

    return result;
}