HDU1001 Sum Problem

• Problem Description
  Hey, welcome to HDOJ(Hangzhou Dianzi University Online Judge).
  In this problem, your task is to calculate SUM(n) = 1 + 2 + 3 + … + n.

• Input
  The input will consist of a series of integers n, one integer per line.

• Output
  For each case, output SUM(n) in one line, followed by a blank line. You may assume the result will be in the range of 32-bit signed integer.

• Sample Input
  1
  100

• Sample Output
  1

  5050

• Author
  DOOM III

• 代码

#include<stdio.h>
int main(){
    int long long a;
    while(scanf("%d",&a)!=EOF){
        printf("%lld\n\n",(a+1)*a/2);
    }
    return 0;
}