（一）、#include <iostream.h>
using namespace std;
class point
{
public:point(int x1=0,int y1=0):x(x1),y(y1){}
       friend ostream& operator<<(ostream&, const point&);
      
       friend istream& operator>>(istream&,point&);
       int x,y;     
};
ostream& operator<<(ostream& out, point& src)
{
    out<<"<"<<src.x<<","<<src.y<<">";
    return out;
}
istream& operator>>(istream& in,point& target)
{
    in>>target.x>>target.y;
    return in;
}
int main()
{
    point a(1,2);
    cin>>a;
    cout<<a;
    return 0;
}
（二）、#include <iostream.h>
class point
{
    int x,y;
public:
    point(int x1=0,int y1=0):x(x1),y(y1){}      
    friend ostream& operator<<(ostream&, const point&);     
    friend istream& operator>>(istream&, point&);
};
ostream& operator<<(ostream& out, const point& src)
{
    out << "<" << src.x << "," << src.y << ">";
    return out;
}

istream& operator>>(istream& in,point& target)
{
    in>> target.x >> target.y;
    return in;
}
int main()
{
    point a(1,2);
    cin>>a;
    cout<<a;
    return 0;
}
为什么换个头文件“#include <iostream.h>”成
（二）就能够运行！？？

在C++编程里，什么时候用“#include<iostream> using namespace std;”？什么时候又用“#include <iostream.h>”？