[说明]
下面程序定义了一个类Shape及其成员函数，然后从类Shape派生出类Point、 类Circle、类Cylinder，以及它们的成员函数。
[C++程序]
#include "iostream.h"
class Shape
public:
virtual void printShapeName() const=0; //纯虚函数
virtual float area() const return 0.0;
virtual float volumn() const return 0.0;
;
class Point: public Shape
public:
Point (float a=0, float b=0)
(x=a; y=b; )
void setPoint(float a,float b)
(x=a; y=b;)
float getX() constreturn x;
float getY() constreturn y;
virtual void printShapeName()const
(1) ;
private：
float x,y;
;
class Circle: (2)
public：
Circle(float r=0.0, float a=0.0, float b=0 .0)
:Point (a,b)
radius=r＞0 r:0;
void setRadius(float r)
radius=r＞0 r:0;
float getRadius () const
return radius;
virtual float area () const
return 3 .14 259*radius*radius ;
virtual void printShapeName () const
cout＜＜"circle:";
private :
float radius;
;
class Cylinder: (3)
public :
Cylinder(float h=0.0,float r=0.0,float x=0.0,float y=0.0)
: (4)
height=h＞0 h:0;
void setHeight (float h)
height=h＞0 h:0;
virtual float area () const
return (5) ;
virtual float volumn () const

float r=Circle:: getRadius ();
return 3.14159*r*r*height;

virtual void printShapeName () const
(cout＜＜"cylinder: " ;
private :
float height;

室内观赏植物如何选择？