1001 A+B Format (20 分)

PAT原題

【注】轉載自柳婼女神的 1001. A+B Format (20)-PAT甲級真題

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 −10⁶≤a,b≤10⁶​​ . 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 <bits/stdc++.h>  
#include <string>
using namespace std;  

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