f(n)计算

#include<stdio.h>
int main()
{
int n=20;
int i;
double sum=0.0;
double sign=1.0;
for(i=1;i<=n;i++)
{
    sum+=sign/i;
    sign=-sign;
}
printf("f(%d)=%f\n",n,sum);
return 0;
}