[说明]
下面程序定义了一个类Point及其成员函数，然后从类Point派生出类Circle及其成员函数。
[C++程序]
//POINT. H
#ifndef POINT_H
# define POINT_H
class Point
public:
Point (float x=0,float y=0) ;
void setPoint (float, float) ;
float getX () const return x;
float getY () const return y;
protected:
float :x,y;
;
#endif
//POINT.CPP
#include ＜iostream.h＞
#include " point .h "
Point :: Point (float a, float b)
x=a; y=b
void Point::setPoint(float a,float b)
x=a; y=b
//CIRCLE . H
#ifndef CIRCLE_H
#define CIRCLE_H
#include "point.h"
class Circle: (1)
public :
Circle (float r=0.0, float x=0, float y=0) ;
void setRadius (float) ;
float getRadius () const;
float area() const;
protected:
float radius;
;
//CIRCLE.CPP
#include "iostream.h"
#include "circle .h "
Circle::Circle(float r,float a,float b)
: (2)
radius=r;
void Circle::setRadius (float r)
radius=r;
float Circle::getRadius () const
return radius;
float Circle::area () const
return 3 .14159*radius*radius ;
//text.cpp
#include ＜iostream.h＞
#include " point .h "
#include " circle .h "
main ()

Circle c(2.5,3.7,4.3) ;
cout＜＜ "X coordinate is "＜＜c.getX ()
＜＜\n Radius is: "＜＜c.getRadius ();
(3) ; //设置新的圆心 (2,2) 。
Point ＆pRef=c;
cout＜＜"\n Circle printed as a point is:"
＜＜"]"＜＜ (4) ＜＜"."＜＜ (5) ＜＜"]";