HDOJ--1001Sum Problem

原题链接

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

 

思路：简单的算术求和

1.使用for循环相加

#include<stdio.h>
 
 int main()
 {
 	int i,n,sum;
 	while(scanf("%d",&n)!=EOF)
 	{
 		sum=0;
 		for(i=1;i<=n;i++)
 			sum+=i;
 		printf("%d\n\n",sum);
	 }
 	return 0;
 }

PS:使用公式求和会造成数据溢出，不能AC，

在这里a1+an=1+n，只需要将n或1+n能除以2的先除，然后再相乘即可