hdu 1001 Sum Problem 的解题报告

链接：http://acm.hdu.edu.cn/showproblem.php?pid=1001

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

 

#include<stdio.h>
 2  int main()
 3 {
 4  int a;
 5 int i;
 6 while(scanf("%d",&a)!=EOF)
 7 {
 8 int sum=0;
 9 if(a==1) sum=1;
10 else
11 {
12 for( i=1;i<=a;i++)
13 {
14 
15    sum=sum+i;
16 }
17 }
18 printf("%d",sum);
19     printf("\n\n");
20 
21 }
22 return 0;
23 }
24  

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