HDU

Sum Problem HDU - 1001

---

Problem

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

ps：仔细看样例，注意用数学公式

代码如下：

#include<iostream>  #include<cstdio>  #include<cstring>  #include<algorithm> #include<string.h> using namespace std; int main() {    long long n, sum;    while(~scanf("%lld", &n)) {        sum = (1+n)*n/2;           //求和公式         printf("%lld\n\n", sum);   //输出后还有一行     }    return 0;}