HDU 1001【Sum Problem】

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

Sum Problem

Time Limit: 1000/500 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)

Total Submission(s): 453970    Accepted Submission(s): 114251

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

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