代码如下，运行结果老是出错求指教
#include<iostream>
int main()
{
    using namespace std;
    //求x 的n次幂
    double x,n,y;
    y = 1;
    int z = 0;
    double xn(double x,double n,double y,int z);
    cout<<"请输入 x 和 n : ";
    cin >> x >> n;
    cout << endl
          << "x 的 n 次幂为 :"
          << xn(x,n,y,z);
}
double xn (double x,double n,double y,int z)
{
    if ( z = 0 )                    //定义了z 在第一轮判断 n >0 or n ==0 or n < 0
    {
        z = 1;
        if ( n > 0 )
            xn (x,n,y,z);
        if ( n == 0 )
            if ( x == 0 ) return 0;
            else return 1;
        if ( n < 0 )
        {    n = -n;
            xn (1/x,n,y,z);
        }
    }
    else
    {
        y *= x;
        if ( --n > 0 )
            xn(x,n,y,z);
        else return y;
    }
}