【PAT (Advanced Level) Practice】1001 A+B Format (20 分)

Calculate $a+b$ and output the sum in standard format – that is, the digits must be separated into groups of three by commas (unless there are less than four digits).

Input Specification:
Each input file contains one test case. Each case contains $a$ pair of integers a and $b$ where $−10^6≤a,b≤10^6$. The numbers are separated by a space.

Output Specification:
For each test case, you should output the sum of $a$ and $b$ in one line. The sum must be written in the standard format.

Sample Input:

-1000000 9

Sample Output:

-999,991

#include<iostream>

using namespace std;

int main(){
    
    int a, b;
    
    cin >> a >> b;
    int c = a + b;
    
    string s = to_string(c);
    string res;
    for(int i = s.size() - 1, j = 0; i >= 0; i--){
        
        res = s[i] + res;
        j++;
        if(j % 3 == 0 && i && s[i - 1] != '-'){
            res = ',' + res;
            j = 0;
        }
    }
    
    cout << res << endl;
    
    return 0;
}