PAT-Advanced-【1001】A+B Format

【1001】A+B Format（20分）

#include<iostream>
#include<string>
using namespace std;
int main() {
    int a, b;
    int sum = 0;
    cin >> a >> b;
    sum = a + b;
    string s = to_string(sum);
    for (int i = 0; i < s.length(); i++) {
        cout << s[i];
        if (s[i] == '-')
            continue;
        if ((i + 1) % 3 == s.length() % 3 && i != s.length() - 1)
            cout << ",";
    }
    return 0;
}