用循环语句来写，刚学C语言

根据用户输入的正整数n，求1-1/2+1/3-1/4+一直加到+(-1)^（n+1）/n的值

#include<stdio.h>
int main()
{
    int n,i = 0;
    double sum = 0;
    int flag = 1;
    printf("请输入n的值:\n");\
    scanf("%d",&n);
    for (i = 1; i <= n; i++)
    {
        sum = sum + flag * (1.0 / i);
        flag = -flag;
    }
    printf("结果为：%lf ", sum);
    return 0;
}

#include"stdio.h"
int main()
{
    int i , n , flag = 1;
    float s = 0;
    printf("put in n:");
    scanf("%d",&n);      
    for(i=1;i<=n;i++)
    {
        s += 1.0 / i * flag;
        flag *= - 1;
    }    
    printf("%f\n", s);
    return 0;
}