Inheritance Principle

Inheritance is a way of extending class. The new class (child class) builds logic on the top of the parent class (super class).

Here's an example:

#include <iostream>
#include <string>

using namespace std;

// Base class:
class Vehicle
{
protected:
    string make;
    string model;

public:
    void representation()
    {
        cout << make << " " << model << endl;
    }

double getInsuranceCost(int months)
    {
        return 0;
    }

string getMake()
    {
        return make;
    }

string getModel()
    {
        return model;
    }
};

// Car inherits Vehicle:
class Car : public Vehicle
{
private:
    // Adds class member:
    int doorsCount;
public:
    // Overwriting method:
    double getInsuranceCost(int months)
    {
        return months * 25;
    }

// Adding constructor:
    Car(string makeValue, string modelValue,
        int doorsCountValue)
    {
        make = makeValue;
        model = modelValue;
        doorsCount = doorsCountValue;
    }

// Method extension:
    void representation()
    {
        Vehicle::representation();

cout << "Doors count: "
            << doorsCount << endl;
    }

// Adding new method:
    int getDoorsCount()
    {
        return doorsCount;
    }
};

void main()
{
    Car car("Toyota", "Corolla", 4);

// Method that was extended:
    car.representation();

cout << "------" << endl;
    // Method that was added:
    cout << car.getDoorsCount() << endl;
    cout << "------" << endl;

// Methods that weren't changed:
    cout << "Make: " << car.getMake() << endl;
    cout << "Model: " << car.getModel() << endl;
    cout << "------" << endl;

// Method that was overwritten:
    cout << "Insurance cost: " <<
        car.getInsuranceCost(12) << " $";

}

Output:

Basically the child class can add, extend, rewrite or use the inherited logic from the parent.

For this example:

Added logic:
- member - doorsCount (line 40)
- parametrized constructor (line 49)
- getter for doorsCount (line 67)
Extended logic:
- representation method (line 58)
Entirely rewritten logic:
- getInsuranceCost (line 43)
Not modified logic:
- getMake (line 24)
- getModel (line 29)