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.
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;
}