题解 | #牛牛学数列#

#include <stdio.h>

int main() {

    /*int n = 0;//初始化
    scanf("%d", &n);//输入
    int i = 0;//遍历
    int sum1 = 0;//奇数项
    int sum2 = 0;//偶数项
    for (i = 1; i <= n; i+=2)
    {

        sum1 = sum1 + i;
        
    }
    for (i = 2; i <= n; i+=2)
    {
        sum2 = sum2 + i;
    }
    int sum = sum1 - sum2;//结果
    printf("%d\n", sum);//输出
    */
    int n = 0;//初始化
    scanf("%d", &n);//输入
    int i = 0;//遍历
    int x = 0;//取出i的值
    int sum = 0;
    for (i = 1; i <= n; i++)
    {
        x = i;
        if (x % 2 == 0)
        {
            x *= -1;
        }
        
        sum = sum + x;
    }
    printf("%d\n", sum);
    return 0;
}