[PAT Advanced Level]1001. A+B Format (20)

#include <iostream>  
#include <string>  
#include <sstream>  
using namespace std;  
  
int main()  
{  
      
    int a,b;  
    cin>>a>>b;  
    int c = a + b;  
    stringstream strStream;    
    strStream<<c;         //int转string的方法！  
    string s = strStream.str();  
  
    for(int i = s.size() - 3; i > 0 && s[i - 1] != '-'; i -= 3)  
        s.insert(i, ",");  
  
    cout<<s<<endl;