南阳理工：sum of all integer numbers

sum of all integer numbers

时间限制：1000 ms  |  内存限制：65535 KB

难度：0

描述

Your task is to find the sum of all integer numbers lying between 1 and N inclusive.

输入

There are multiple test cases.
The input consists of a single integer N that is not greater than 10000 by it's absolute value.

输出

Write a single integer number that is the sum of all integer numbers lying between 1 and N inclusive.

样例输入

3

样例输出

6

注意：一定要看清楚题，是1——N之间的数求和，N可能为负值。另外，由于N的绝对值有限定，所以可以直接用公式计算而不会溢出，否则要分情况讨论做，先用偶数部分除以二在求和。

#include<stdio.h>
int main()
{
   int n;
   while(scanf("%d",&n)!=EOF)//由于开始不小心误写成了NULL，所以一直超时，所以写代码时一定要小心啊！
   {
         if(n>0) printf("%d\n",(n+1)*n/2);     
          else printf("%d\n",1-n*(n-1)/2);
              
    }
  return 0;
}