PAT Advanced 1001 A+B Format（20）

题目描述：

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

算法描述：模拟输出 字符串处理

题目大意：

给出一个数，每三位一个逗号输出

#include<iostream>
using namespace std;
int main()
{
    int  A, B;
    cin >> A >> B;
    int C = A + B;
    string num = to_string(C);
    string res;
    
    for(int i = num.size() - 1 , j = 0 ; i >= 0 ; i-- ){
        res = num[i] + res ;
        j++;
        if( j % 3 == 0 && i && num[i - 1] != '-')
            res = ',' + res;
    }
    cout << res ;
    return 0;
}