03. Inheritance

Inheritence

In our everyday life, we tend to divide things into groups, based on their shared characteristics. Here are some groups that you have probably used yourself: electronics, tools, vehicles, or plants.

Sometimes these groups have hierarchies. For example, computers and smartphones are both types of electronics, but computers and smartphones are also groups in and of themselves. You can imagine a tree with "electronics" at the top, and "computers" and "smartphones" each as children of the "electronics" node.

Object-oriented programming uses the same principles! For instance, imagine a Vehicle class:

class Vehicle {
public:
  int wheels = 0;
  string color = "blue";

  void Print() const
  {
    std::cout << "This " << color << " vehicle has " << wheels << " wheels!\n";
  }
};

We can derive other classes from Vehicle, such as Car or Bicycle. One advantage is that this saves us from having to define all of the common member variables: in this case, wheels and color.

Another benefit is that the derived classes, Car and Bicycle, can have distinct member variables, such as sunroof or kickstand. Different derived classes will have different member variables:

class Car : public Vehicle {
public:
  bool sunroof = false;
};

class Truck : public Vehicle {
public:
  bool kickstand = true;
};

Instructions

1. Add a new member variable to class Vehicle.
2. Output that new member in main().
3. Derive a new class from Vehicle, alongside Car and Bicycle.
4. Instantiate an object of that new class.
5. Print the object.