p410 例12.4 虚函数和虚基类的应用.cpp

谭浩强 《C++ 程序设计》第三版的部分课后练习题源码

#include<iostream>
using namespace std;
class Shape
{
      public:
      Shape(){}
      virtual float area()const {return 0;}
      virtual float volume()const {return 0;}
      virtual void showname()const=0;
      virtual void display() const =0;
};              
      
class Point:public Shape
{
      private:
              float x,y;
      public:
             Point(float a=0,float b=0):x(a),y(b){}
             void showname() const{ cout<<"the information of a point: ";}
             void display()const;
};        
        
void Point::display()const
{
     cout<<"x="<<x<<"   y="<<y<<endl;
}     
     
     

  
class Circle:public Point
{
      protected:
              float r;
             
      public:
             Circle(float a,float b,float c):Point(a,b),r(c){}
             float area()const;
             void showname()const { cout<<"the information of the circle :"; }
             void display()const;
      
      
};   

float Circle::area()const
{
      return 3.1415*r*r;
}      
      

void Circle::display() const 
{
     Point::display();
     cout<<"  r="<<r<<endl;
      
}     


class Cylinder:public Circle
{
      private:
              float height;
      public:
             Cylinder(float a=0,float b=0,float c=0,float d=0):Circle(a,b,c),height(d){}
             float area()const ;
             float volume()const ; 
             void showname()const;
             void display() const; 
};       
  
float Cylinder::area()const
{
      return 2*Circle::area()+2*3.1415*r*height;
      
}      
          
float Cylinder::volume()const
{
     return Circle::area()*height; 
      
}       
 
void Cylinder::showname()const
{
     cout<<"the information of the cylinder: ";
     
} 

void Cylinder::display()const
{
     Circle::display();
     cout<<"the height="<<height<<endl;
}      
         
 
     
int main()
{
    Point p(23.4,56);
    Shape *s=&p;
    s->showname();
    s->display();
    cout<<"the area ="<<s->area()<<endl;
    cout<<"the volum ="<<s->volume()<<endl;
    
    Circle c(34,23,4);
    s=&c;
    s->showname();
    s->display();
    cout<<"the area ="<<s->area()<<endl;
    cout<<"the volum ="<<s->volume()<<endl;
    
    Cylinder cy(23,45,24,12);
    s=&cy;
    s->showname();
    s->display();
    cout<<"the area ="<<s->area()<<endl;
    cout<<"the volum ="<<s->volume()<<endl;
    
    system("pause");
    return 0;  
}