PAT 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

Each input file contains one test case. Each case contains a pair of integers a and b where -1000000 <= a, b <= 1000000. The numbers are separated by a space.

Output

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

题目意思：A+B求和，然后每三位为一个单位加上一个“,”的格式输出。
解题思路：转换成字符串来遍历会很方便，注意若是负数第一位负号也要占位的，并且要求最后一位不能出现“,”，其实可以看看遍历到当前位时剩下的位数若是3的倍数，那么就需要加“,”了。

#include<iostream>
#include<algorithm>
#include<string>
using namespace std;
int main()
{
    int a,b,len;
    int i;
    string str;
    cin>>a>>b;
    str=to_string(a+b);
    len=str.size();
    for(i=0;i<len;i++)
    {
        cout<<str[i];
        if(str[i]=='-')
        {
            continue;
        }
        if((len-i-1)%3==0&&i!=len-1)
        {
            cout<<",";
        }
    }
    return 0;
}

注意这里的to_string是C++11里面string中所包含的函数。