第六章

(1)#include <iostream>using namespace std;  class Point  {public:      Point(float x=0,float y=0);      void setPoint(float,float);      float getX() const      {return x;}      float getY() const      {return y;}      friend ostream & operator<<(ostream &output,Point &);  protected:      float x,y;  };  Point::Point(float a,float b)  {      x=a;y=b;  }  void Point::setPoint(float a,float b)  {   x=a;y=b;  }  ostream & operator<<(ostream &output,Point &p)  {   output<<"["<<p.x<<","<<p.y<<"]"<<endl;   return output;  }  class Circle:public Point  {  public:      Circle(float x,float y,float r):Point(x,y),radius(r){}      void setRadius(float r)      {radius=r;}      float getRadius() const      {return radius;}      double area() const      {       return 3.1415*radius*radius;      }      friend ostream & operator<<(ostream &output,Circle &);  protected:      float radius;  };  ostream & operator<<(ostream &output,Circle &c)  {      output<<"Center =["<<c.x<<","<<c.y<<"],r= "<<c.radius<<",area="<<c.area()<<endl;      return output;  }  class Cylinder:public Circle  {  public:      Cylinder(float x,float y,float r,float h):Circle(x,y,r),height(h){}      void setHeight(float h)      {height=h;}      float getHeight() const      {return height;}      double area() const      {          return 2*Circle::area()+2*3.1415*radius*height;       }      double volume() const      {          return 3.1415*radius*radius*height;      }      friend ostream & operator<<(ostream &output,Cylinder &);  protected:      float height;  };  ostream & operator<<(ostream &output,Cylinder &cy)  {   output<<"Center=["<<cy.x<<cy.y<<"],r="<<cy.radius<<",h="<<cy.height<<"\narea="<<cy.area()<<",volume="<<cy.volume()<<endl;   return output;  }  int main()  {   Cylinder cy1(3.5,6.4,5.2,10);   cout<<"original cylinder:\nx="<<cy1.getX()<<",y="<<cy1.getY()<<",r="<<cy1.getRadius()<<",h="<<cy1.getHeight()<<"\narea="<<cy1.area()<<",volume="<<cy1.volume()<<endl;   cy1.setHeight(15);   cy1.setRadius(7.5);   cy1.setPoint(5,5);   cout<<"\nnew cylinder:\n"<<cy1;   Point &pRef=cy1;   cout<<"\npRef as a point:"<<pRef;   Circle &cRef=cy1;   cout<<"\ncRef as a circle:"<<cRef;   return 0;  }  <img src="http://img.blog.csdn.net/20150526171227603" alt="" />(3)1 . #include <iostream>  using namespace std;  class Point  {   public:       Point(float a,float b):x(a),y(b){}       ~Point(){cout<<"executing Point destructor"<<endl;}   private:       float x;       float y;  };  class Circle:public Point  {  public:      Circle(float a,float b,float r):Point(a,b),radius(r){}      ~Circle(){cout<<"executing Circle destructor"<<endl;}  private:      float radius;  };  int main()  {   Point *p=new Circle(1,2,3);   delete p;   return 0;  }  <img src="http://img.blog.csdn.net/20150526171306277" alt="" />

2 . #include <iostream>  using namespace std;  class Point  {   public:       Point(float a,float b):x(a),y(b){}       ~Point(){cout<<"executing Point destructor"<<endl;}   private:       float x;       float y;  };  class Circle:public Point  {  public:      Circle(float a,float b,float r):Point(a,b),radius(r){}      ~Circle(){cout<<"executing Circle destructor"<<endl;}  private:      float radius;  };  int main()  {   Point *p=new Circle(1,2,3);   Circle *r=new Circle(1,2,3);   delete r;   return 0;  } <img src="http://img.blog.csdn.net/20150526171312204" alt="" />3 .  #include <iostream>  using namespace std;  class Point  {   public:       Point(float a,float b):x(a),y(b){}       virtual ~Point(){cout<<"executing Point destructor"<<endl;}   private:       float x;       float y;  };  class Circle:public Point  {  public:      Circle(float a,float b,float r):Point(a,b),radius(r){}      ~Circle(){cout<<"executing Circle destructor"<<endl;}  private:      float radius;  };  int main()  {   Point *p=new Circle(1,2,3);   delete p;   return 0;  } <img src="http://img.blog.csdn.net/20150526171312204" alt="" />(4)#include <iostream>using namespace std;  class Shape{  public:      virtual double area()const =0;  };  class Circle:public Shape  {  public:      Circle(double r):radius(r){}      virtual double area() const      {       return 3.1415*radius*radius;      }  protected:      double radius;  };  class Rectangle :public Shape{  public:      Rectangle(double l,double w):length(l),width(w){}      virtual double area()const      {       return length*width;      }  protected:      double length;      double width;  };  class Triangle:public Shape  {  public:      Triangle(double d,double h):dibian(d),height(h){}      virtual double area() const      {       return 0.5*dibian*height;      }  protected:      double dibian;      double height;  };  void display(const Shape &s)  {   cout<<s.area()<<endl;  }  int main()  {   Circle c(4);   cout<<"area of c is ";   display(c);   Rectangle r(2,4);   cout<<"area of r is ";   display(r);   Triangle t(1,2);   cout<<"area of t is ";   display(t);   return 0;  }<img src="http://img.blog.csdn.net/20150526171317519" alt="" />(5)#include <iostream>using namespace std;  class Shape{  public:      virtual double area()const =0;  };  class Circle:public Shape  {  public:      Circle(double r):radius(r){}      virtual double area() const      {       return 3.1415*radius*radius;      }  protected:      double radius;  };  class Rectangle :public Shape{  public:      Rectangle(double l,double w):length(l),width(w){}      virtual double area()const      {       return length*width;      }  protected:      double length;      double width;  };  class Triangle:public Shape  {  public:      Triangle(double d,double h):dibian(d),height(h){}      virtual double area() const      {       return 0.5*dibian*height;      }  protected:      double dibian;      double height;  };  class Square:public Shape{  public:      Square(double s):side(s){}      virtual double area() const      {       return side*side;      }  protected:      double side;  };  class Trapezoid:public Shape  {  public:      Trapezoid(double t,double b,double h):top(t),bottem(b),height(h){}      virtual double area() const      {       return 0.5*(top+bottem)*height;      }  protected:      double top,bottem,height;  };  void display(const Shape &s)  {   cout<<s.area()<<endl;  }  int main()  {   Circle c(4);   Rectangle r(2,4);   Triangle t(1,2);   Square s(2);   Trapezoid tt(1,2,3);   Shape *p[5]={&c,&r,&t,&s,&tt};   double area=0.0;   for(int i=0;i<5;i++)   {    area=area+p[i]->area();   }   cout<<"the sum of area is "<<area<<endl;   return 0;  }