URAL 1068. Sum （小学数学题）

1068. Sum

Time limit: 2.0 second
Memory limit: 64 MB

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

Input

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

Output

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

Sample

inputoutput

-3

-5

题意：给一个整数N，求1~N的连续和。

解析：N可正可负。

AC代码：

#include <cstdio>int main(){    int n, sum;    while(scanf("%d", &n)==1){        sum = 0;        if(n < 1) sum = n*(1 - n)/2 + 1;        else sum = n*(n+1)/2;        printf("%d\n", sum);    }    return 0;}