Class pointer and virtual function

#include <iostream>
using namespace std;

class figure {
protected:
  double x, y;
public:
  void set_dim(double i, double j=0) {
    x = i;
    y = j;
  }
  virtual void show_area() {
    cout << "No area computation defined ";
    cout << "for this class.\n";
  }
} ;

class triangle : public figure {
  public:
    void show_area() {
      cout << "Triangle with height ";
      cout << x << " and base " << y;
      cout << " has an area of ";
      cout << x * 0.5 * y << ".\n";
    }
};

class rectangle : public figure {
  public:
    void show_area() {
      cout << "Rectangle with dimensions ";
      cout << x << "x" << y;
      cout << " has an area of ";
      cout << x *  y << ".\n";
    }
};

class circle : public figure {
  public:
    void show_area() {
      cout << "Circle with radius ";
      cout << x;
      cout << " has an area of ";
      cout << 3.14 * x * x << ".\n";
    }
} ;
  
int main()
{
  figure *p;  // create a pointer to base type

  triangle t; // create objects of derived types
  rectangle s;
  circle c;

  p = &t;
  p->set_dim(10.0, 5.0);
  p->show_area();

  p = &s;
  p->set_dim(10.0, 5.0);
  p->show_area();  

  p = &c;
  p->set_dim(9.0);
  p->show_area(); 

  return 0;
}

Related examples in the same category

1.	A simple example using a virtual function.
2.	Virtual functions are hierarchical.
3.	Virtual function: respond to random events
4.	Use virtual function to define interface.
5.	Virtual functions retain virtual nature when inherited.
6.	Virtual function and public inheritance
7.	Virtual function and three level inheritance
8.	Virtual function for two derived classes

Class pointer and virtual function : Virtual « Function « C++

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