PAT Advanced 1001 A+B Format

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

三位一组输出a+b的结果。从右至左每三位插入一个逗号，注意最低位右侧和最高位左侧的判断。

#include <iostream>
#include <sstream>
using namespace std;
int main()
{
    int a,b;
    cin>>a>>b;
    stringstream ss;
    ss<<a+b;
    string ans;
    ss>>ans;
    string tans="";
    int len=ans.length(),start=0;
    if(len>1&&ans[0]=='-'){start=1;len--;tans+='-';}
    for(int i=0;i<len;i++)
    {

        if((len-i)%3==0&&i!=len-1&&i!=0)
        {
            tans+=',';
        }
        tans+=ans[i+start];
    }
    cout<<tans<<endl;
    return 0;
}