题解 | #牛牛学数列3#

#include<stdio.h>
int main()
{
    int i = 0;
    int n;
    double sum = 0.0, sign = 1;
    int flag = 1;
    while (scanf("%d", &n) != EOF)
    {
        for (i = 1; i <= n; i++)
        {
            sign = (flag * 1.0) / i;
            sum += sign;
            flag = -flag;
        }
        printf("%.3lf\n", sum);
    }
    return 0;
}