这个不会做，谁能帮帮我

用函数求1+1/2+1/3+……+1/n之和，要求函数原型为“double fnsum(int n)”。

#include<stdio.h>
double fnsum(int n)
{
    int i;
    double sum = 0;
    for(i = 1; i <= n; i++)
        sum += (double)1.0/(double)i;
    return sum;
}
int main()
{
    double sum;
    int n = 5;
    sum = fun(n);
    printf("sum = %lf\n",sum);
    return 0;
}