南阳acm 436 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

#include<stdio.h>

int main()
{
int n,i,t;
while(scanf("%d",&n)!=EOF)
{
if(n>0)
    printf("%d\n",n*(n+1)/2);
else if(n==0)
printf("1\n");
else{
t = -n;
printf("%d\n",-(1+t)*t/2+1);
}
}
return 0;
}