求大佬看下开平方的函数（牛顿迭代法），感激涕零！

#include
#include
using namespace std;

//x(n + 1) = (xn+a/xn)/2
void NewtonSqrt(double a,double &x){
a = x - (x + a / x) / 2;
if (a<= 0.00001)
return;
x = (x + a / x) / 2;
NewtonSqrt(a, x);
}

void main(){
double a = 3;
double x = a / 2;
cout << x <<endl;
_getch();
}