Problem – 1001
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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
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题目比较简单，直接上代码：
#include<stdio.h>
#include<math.h>
#include<string.h>
int main()
{
long n;
while(scanf("%ld",&n)!=EOF)
printf("%ld\n\n", n%2? (n+1)/2*n: n/2*(n+1));
return 0;
}
唯一要注意的地方是防止(n+1)*n导致数据溢出，这里使用技巧分n的奇偶进行条件计算
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