杭电ACM 1001（Sum Problem）

#include<iostream>
using namespace std;
int main()
{
      int n;
      signed int sum;//有符号整形
     while(cin>>n)
     {
         sum=0;
         for(int i=0;i<=n;i++)
             sum+=i;
         cout<<sum<<"\n"<<"\n";//followed with a blank line!
     }
     return 0;
}