HSC: Virtual Keyword

/* A virtual member is a member function that can be redefined in a derived class, while preserving its calling properties through references. The syntax for a function to become virtual is to precede its declaration with the virtual keyword:
*/

#include<iostream.h>
#include<conio.h>


class vehicle
{
protected: float mileage;
public:
    vehicle(float m1)
    {
    mileage=m1;
    }

    virtual void display()
    {
    cout<<"vehicle details:\n";
    }

};


class two:public vehicle
{
char clutch;
public:
    two(float m1,char c):vehicle(m1)
    {
    clutch=c;
    }

    void display()
    {
     cout<<"\nMileage: "<<mileage;
     cout<<"\nClutch: "<<clutch;
     }
};

class four:public vehicle
{
    char ac;
    public:
      four(float m1, char c):vehicle(m1)
      {
      ac=c;
      }

      void display()
      {

     cout<<"\nMileage:"<<mileage;
     cout<<"\nAC:"<<ac;
     }
};


void main()
{
vehicle *b;
clrscr();

two activa(40,'y');
b=&activa;
b->display();

four maruti(17,'n');
b=&maruti;
b->display();

four bmw(5,'y');
b=&bmw;
b->display();
getch();
}