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

题目链接：https://pintia.cn/problem-sets/994805342720868352/problems/994805528788582400

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 −. 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>
 #include <cstdio>
 #include <string>
 #include <cstring>
 #include <algorithm>
 #include <stack>
 using namespace std;
 int main()
 {
        int n,m,sum;
        while(cin>>n>>m){
            sum=n+m;
            if(sum==){
                cout<<<<endl;
                continue;
            }
            int flag=;
            if(sum<){
            flag=;
            sum=-sum;
            }
            char c='-';
            stack<char> s;
            int t=;
            while(sum){
                c=sum%+'';
                s.push(c);
                t++;
                if(t%==&&sum/) s.push(',');
                sum/=;
            }
            if(flag) s.push('-');
            while(!s.empty()){
                cout<<s.top();
             s.pop();
            }
            cout<<endl;
        }
     return ;
 }