PAT 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

注意:
    1. 每三位加一个逗号,是从低位开始数,即1002输出的应该是1,002而非100,2
    2. 注意结果可能为负数,要输出负号
    3. 和为0的话,直接输出0即可

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
vector<int> vect;
vector<char> ans_vect;
int main(){
    bool flag = false;
    int a,b,ans;
    cin>>a>>b;
    ans = a + b;
    if (ans < 0){
        flag = 1;
        ans = -1 * ans;
    }

    while(ans){
        int t = ans % 10;
        vect.push_back(t);
        ans /= 10;
    }
    
    if (vect.size() == 0){
        cout<<0;
        return 0;
    }
    
    string output = "";
    for (int i = 0; i < vect.size(); ++i){
        output += char(vect[i] + '0');
        if ((i + 1) != vect.size() && (i + 1) % 3 == 0)
            output += ',';
    }
    if (flag) cout<<'-';
    reverse(output.begin(),output.end());
    cout<<output;
    
    return 0;
}