关于高精度减法的问题，如何解决？

Question

高精度减法，求a-b a,b都不超过240位

#include <bits/stdc++.h>
using namespace std;
const int N = 10090;
int a[N], b[N], c[N];
int flag = 0;
int main()
{
    string str1;
    string str2;
    cin >> str1;
    cin >> str2;
    if ((atoi(str1.c_str()) < atoi(str2.c_str()) && str1.size() == str2.size()) || str1.size() < str2.size()){
        swap(str1, str2);
        flag = 1;
    }
    for (int i = 0; i < str1.size(); i ++)
        a[str1.size()-1-i] = str1[i] - '0';
    for (int i = 0; i < str2.size(); i ++)
        b[str2.size()-i-1] = str2[i] - '0';
    int ans = max(str1.size(), str2.size());
    for (int i = 0; i < ans; i ++){
        if (a[i] < b[i]){
            a[i+1] -= 1; 
            a[i] += 10; 
        }c[i] = a[i] - b[i];  
    }
    while (c[ans-1] == 0 && ans > 1)
        ans -= 1;
    if (flag == 1)
        cout << "-";
    for (int i = 0; i < ans; i ++)
        cout << c[ans-1-i];
    return 0;
}

Answer 1

这个代码有什么问题吗