Designing Game Code with Polymorphism - Learn C++ for Game Development - page 121

You create virtual methods by adding the virtual keyword to the beginning of the method signature.
The method GetNumberOfWheels is now a virtual method. To get the benefit of this, Listing 11-2
updates the Car and Motorcycle classes to make their GetNumberOfWheels methods virtual .
Listing 11-2. Making GetNumberOfWheels Virtual in Car and Motorcycle
class Car : public Vehicle
{
public:
Car();
~Car();
virtual unsigned int GetNumberOfWheels() const
{
return 4;
}
};
class Motorcycle : public Vehicle
{
public:
Motorcycle();
~Motorcycle();
virtual unsigned int GetNumberOfWheels() const
{
return 2;
}
};
The code in Listing 11-2 completes our updates to the GetNumberOfWheels methods in the Vehicle ,
Car , and Motorcycle classes. Listing 11-3 modifies the PrintNumberOfWheels method to make use of
polymorphism.
Listing 11-3. Using Polymorphism in PrintNumberOfWheels
void PrintNumberOfWheels()
{
Vehicle vehicle;
Car car;
Motorcycle motorcycle;
Vehicle* pVehicle = &vehicle;
std::cout << pVehicle->GetNumberOfWheels() << std::endl;
pVehicle = &car;
std::cout << pVehicle->GetNumberOfWheels() << std::endl;
pVehicle = &motorcycle;
std::cout << pVehicle->GetNumberOfWheels() << std::endl;
}