循环不能输出，为什么呀

#include
#include
using namespace std;
double sin(double x);
int main()
{double x;
cout<<"please input x:";
cin>>x;
cout<<"output:"<<sin(x);
return 0;}

double sin(double x)
{int n=1;double sum=x;double z=x;
do{

z=zxx*(-1)/2n(2*n-1);
sum=sum+z;
n++;}while(fabs(z)>=1e-5);
return sum;}