Huawei machine test -- high precision integer addition

describe ：

Enter two strings str The whole number represented , Find the sum of the numbers they represent .

Data range ： 1≤len(str)≤10000 

Input description ：

Enter two strings . Ensure that the string contains only '0'~'9' character

Output description ：

Output the sum result

Example 1：

Input ：9876543210

           1234567890

Output ：11111111100

solution ：

This logic , I look like I have bug

#include<stdio.h>
#include<string.h>
#define MAX 10000

int main() {
    char str1[MAX] = {};    
    char str2[MAX] = {};
    int result[MAX] = {0};        //  Store the calculation results 
    scanf("%[^\n]\n", str1);
    scanf("%[^\n]\n", str2);

    int len1 = strlen(str1), len2 = strlen(str2);
    int len = (len1 > len2) ? len1 : len2;
    int count, flag = 0;         //  Represent the result and carry value of each round of calculation respectively 
    for (int i = 0; i < len; i++, len1--, len2--) {
        if (len1 > 0 && len2 > 0) {
            count = str1[len1 - 1] + str2[len2 - 1] - '0' - '0' + flag;
            result[i] = count % 10;
            if (count > 9) {
                flag = 1;
            } else {
                flag = 0;
            }
        } else {
            count = (len1 > len2 ? str1[len1 - 1] : str2[len2 - 1]) - '0' + flag;
            result[i] = count % 10;
            if (count > 9) {
                flag = 1;
            } else {
                flag = 0;
            }
        }
    }
    if (count > 9) {            //  Secondary high if carry , The highest bit is 1
        result[len] = 1;
    }
    //  Output in reverse order 
    if (result[len] != 0) printf("%d", result[len]);
    for (int i = len - 1; i >= 0; i--) {
        if (result[i] >= 0) printf("%d", result[i]);
    }
    printf("\n");

    return 0;
}