multiply two string

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

int main()
{
    char n1[] = "123";
    char n2[] = "56";

    int len1 = strlen(n1);
    int len2 = strlen(n2);
    int n, i;

    if(len1 > len2) n = len1;
    else n = len2;

    char num1[n], num2[n];

    for(i = 0; i < n - len1; i++) {
        num1[i] = '0';
    }

    for(int j = 0; j < n; i++, j++) {
        num1[i] = n1[j];
    }

    for(i = 0; i < n - len2; i++) {
        num2[i] = '0';
    }
    //i = 1
    for(int j = 0; i < n; i++, j++) {
        num2[i] = n2[j];
    }



    char pro[2 * n + 1];

    int j, k;
    for(i = 0; i < 2 * n + 1; i++) {
        pro[i] = '0';
    }
    pro[2 * n] = '\0';

    // num1 - i && num2 - j  && pro - k

    int p, carry = 0, counter = -1;

    for(j = n - 1; j >= 0; j--) {
        carry = 0;
        counter++;
        k = 2 * n - 1 - counter;
        for(i = n - 1; i >= 0; i--) {
            p = pro[k] - '0' + (num1[i] - '0') * (num2[j] - '0') + carry;
            carry = p / 10;
            pro[k] = (p % 10) + '0';
            k--;
        }
        pro[k] = carry + '0';
    }

    //printf("ans = %s\n", pro);

    for(i = 0; i < 2 * n; i++) {
        if(pro[i] != '0') {
            for(j = i; j < 2 * n; j++) {
                printf("%c", pro[j]);
            }
            break;
        }
    }

    return 0;
}