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Learn Object-Oriented Programming in C++

What is Inheritance?

Explore the concept of inheritance in C++ to understand how derived classes inherit data members and functions from base classes. This lesson helps you grasp IS-A relationships, enabling efficient code reuse and better organization through practical examples of Vehicle, Car, and Ship classes.

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Why do We Need Inheritance?

In the classes chapter, we’ve covered the HAS-A relationship. We know a class HAS-A data members and member functions. Now, we want the data members, and member functions of the class are accessible from other classes. So, the capability of a class to derive properties and characteristics from another class is called Inheritance. In inheritance, we have IS-A relationship between classes e.g a car is a vehicle and a ship is a vehicle.

Let’s take the example of Vehicle here.

Vehicle Class

In a Vehicle class, we have many data members like Make, Color, Year and Model. A Vehicle HAS-A Model, Year, Color and Make.

Implementation of Vehicle Class

Let’s look at the implementation of Vehicle class:

C++
class Vehicle{
  protected:
  string Make;
  string Color;
  int Year;
  string Model;
  public:
  Vehicle(){
    Make = "";
    Color = "";
    Year = 0;
    Model = "";
  }
  
  Vehicle(string mk, string col, int yr, string mdl){
    Make = mk;
    Color = col;
    Year = yr;
    Model = mdl;
  }
  void print_details(){
    cout << "Manufacturer: " << Make << endl;
    cout << "Color: " << Color << endl;
    cout << "Year: " << Year << endl;
    cout << "Model: " << Model << endl;
  }
};
int main(){
  Vehicle v("Ford Australia", "Yellow", 2008, "Falcon");  
  v.print_details();
}

The following illustration depicts the structure of the Vehicle class:

These attributes are also attributes of all Cars, Ships and Airplanes but every type of vehicle has some attributes that are different from other types of vehicles, as we will see in detail.

Car Class

The implementation of a Car class needs the same data members and member functions of Vehicle class but we have to include them in the Car class. Cars do have a trunk and every trunk has a capacity to store things upto some limit.

Implementation of Car Class

Let’s look at the implementation of the Car class:

C++
class Car{
  string Make;
  string Color;
  int Year;
  string Model;
  string trunk_size;
  public:
  Car(){
    Make = "";
    Color = "";
    Year = 0;
    Model = "";
    trunk_size = "";
  }
  Car(string mk, string col, int yr, string mdl, string ts){
    Make = mk;
    Color = col;
    Year = yr;
    Model = mdl;
    trunk_size = ts;
  }
  void print_details(){
    cout << "Manufacturer: " << Make << endl;
    cout << "Color: " << Color << endl;
    cout << "Year: " << Year << endl;
    cout << "Model: " << Model << endl;
    cout << "Trunk size: " << trunk_size << endl;
  }
};
int main(){
  Car car("Chevrolet", "Black", 2010, "Camaro", "9.1 cubic feet");
  car.print_details();
}

The following illustration depicts the structure of the Car class:

Ship Class

The implementation of a Ship class needs the same data members and member functions of Vehicle class but we have to include them in the Ship class. Ships do have anchors and they vary in numbers.

Implementation of Ship Class

Let’s look at the implementation of the Ship class:

C++
class Ship{
  string Make;
  string Color;
  int Year;
  string Model;
  int Number_of_Anchors;
  
  public:
  Ship(){
    Make = "";
    Color = "";
    Year = 0;
    Model = "";
    Number_of_Anchors = 0;
  }
  
  Ship(string mk, string col, int yr, string mdl, int na){
    Make = mk;
    Color = col;
    Year = yr;
    Model = mdl;
    Number_of_Anchors = na;
  }
  void print_details(){
    cout << "Manufacturer: " << Make << endl;
    cout << "Color: " << Color << endl;
    cout << "Year: " << Year << endl;
    cout << "Model: " << Model << endl;
    cout << "Number of Anchors: " << Number_of_Anchors << endl;
  }
};
int main(){
  Ship ship("Harland and Wolff, Belfast", "Black and whilte",
            1912, "RMS Titanic", 3);
  ship.print_details();
}

The following illustration depicts the structure of the Ships class:

In the declared classes for different types of vehicles (Car and Ship), we have many repetitive attributes which should be in one base class and should be inherited in the derived classes.