请使用递归算法求下列序列的前n项之和。
            1 + 1/2 - 1/3 + 1/4 -1/5 ......
输入：
        n
输出：
        序列的前n项和（精确到小数点之后第6位）
main()
{
double s;int n,i,t=1;
scanf("%d",&n);
if(n==1)printf("1\n");
else
{
for(i=2;i<=n;i++)
{t=t*i;
s=s+1./t;
t=t>0?-1:1;
}
 printf("%lf",s+1);
}
}

double fun(int n)
{
    int temp=1;
    if(n==1) return 1.0;
   if(n%2==1) temp=-1;
   return 1.0*temp/n+fun(n-1);
}

#include "stdio.h"

double fun(int n)
{
        if(n==1)
        {
                return 1.0;
        }
        else
        {
                double sum,itemn;
                itemn=1.0/n;
                if(n%2==1) itemn=-itemn;
                sum=fun(n-1)+itemn;
                return sum;
        }
}

int main(void)
{
        double sum;
        int n;
        printf("input n=");
        scanf("%d",&n);
        sum=fun(n);
        printf("result=%lf\n",sum);
        return 0;
}