改进的欧拉方法

#include <iostream>
#include<math.h>
#define f(x,y) (y-2*x/y)//(即f(x,y)=y-2*x/y)
using namespace std;
int main()
{
 int n,i;
 double a,b;
 double x0,y0,x1,y1,yc,yp;
 double h;
 cout<<"输入 x的下界:";
 cin>>a;
 cout<<"输入 x的上界:";
 cin>>b;
 cout<<"输入y0的值:";
 cin>>y0;
 cout<<"输入n的值: ";
 cin>>n;
cout<<"输入h的值: ";
 cin>>h;
 x0=a;
for(i=1;i<=n;i++)
 {
  x1=x0+h;
  yp=y0+h*f(x0,y0);
  yc=y0+h*f(x1,yp);
  y1=(yp+yc)/2;
  cout<<"xn的值"<<x1<<endl;
  cout<<"yn的值"<<y1<<endl;
  x0=x1;