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

题目描述：https://pintia.cn/problem-sets/994805342720868352/problems/994805528788582400

考点：

1.stringstream 可实现 int & string 间的类型转换。

int c = a+b;

stringstream ss;
ss<<c;
string c_str = ss.str();

int d;
ss>>d;

2.string.insert(index, “obj”)

3.string.substr(start, length)

代码：

#include<iostream>
#include<sstream>
#include<string>
using namespace std;
int main(){
    int a,b;cin>>a>>b;
    int c = a+b;
    stringstream ss;
    ss<<c;
    string c_str = ss.str();
    if(c<0){
        c_str = c_str.substr(1);        
    }
    int k = c_str.length()-1-2;
    while(k>0){
        c_str.insert(k,",");
        k = k-1-2;
    }
    if(c<0){
        c_str = "-"+c_str;        
    }
    cout<<c_str<<endl;
}