HDU1001 Sum Problem

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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

【源代码】：

#include<stdio.h>int main(void){    int n;    long long sum;    while(scanf("%d",&n)!=EOF)    {        if(n%2)            sum=(n+1)/2*n;        else            sum=n/2*(n+1);        printf("%I64d\n\n",sum);    }    return 0;}

【注】：

1、注意格式，输出独占一行，还需再输出一行
2、注意大数。用%I64d输出
3、以前一直用的cin,cout...scanf,printf在格式控制上做得更好些
4、先对n进行判断。

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