Welcome back! Now that you have a solid understanding of classes and objects in C++, it's time to build on that knowledge by exploring inheritance. Consider it a natural progression in our journey into object-oriented programming (OOP).

Inheritance allows you to create a new class based on an existing class. By using inheritance, you can reuse code, add new features, and make your programs easier to manage and understand. Let's dive in and see what it's all about.

In this lesson, you'll understand how to use inheritance in C++. We'll cover:

1. What Inheritance Is
2. How to Implement Inheritance in C++
3. Why Inheritance Is Beneficial

Inheritance is a way to establish a relationship between a new class (derived class) and an existing class (base class). The derived class inherits properties and behaviors (methods) from the base class.

Here’s a simple example:

C++
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1#include <iostream>
2#include <string>
3
4// Define the base class Person with name and age attributes
5class Person {
6public:
7    // Constructor to initialize name and age
8    Person(const std::string& name, int age) : name(name), age(age) {}
9
10    // Display method to show name and age
11    void display() const {
12        std::cout << "Name: " << name << ", Age: " << age << std::endl;
13    }
14
15    // Greet method to display a greeting message
16    void greet() const {
17        std::cout << "Hello, there!" << std::endl;
18    }
19
20private:
21    std::string name;
22    int age;
23};
24
25// Define the derived class Student, inheriting from Person
26class Student : public Person {
27public:
28    // Constructor to initialize name, age of the base class, and the major of the student
29    Student(const std::string& name, int age, const std::string& major)
30        : Person(name, age), major(major) {}
31
32    // Display method to show name, age using the base class display method, and major of the student
33    void display() const {
34        this->greet();
35        Person::display();
36        std::cout << "Major: " << major << std::endl;
37    }
38
39private:
40    std::string major;
41};
42
43int main() {
44    // Create a Student object and display its details
45    Student student("Bob", 25, "Computer Science");
46    student.display();
47
48    return 0;
49}

In this snippet, the Student class inherits from the Person class. It reuses the name and age attributes and methods from the Person class and adds a new attribute major and a new display method to show the student's major.

When you declare a derived class, you specify the base class it inherits from. This is done using the : public BaseClass syntax. The derived class can then extend or override the functionality of the base class.

In our example:

• The Person class is the base class.
• The Student class is the derived class, inheriting name and age from the Person class.
• The Student class also adds a new member, major, and overrides the display method to include information about the major.
  • Notice how Student::display() calls Person::display() to reuse the base class functionality before adding its own details.
  • The greet method is also called from the display method to show how the derived class can access base class methods using the this pointer.

Notice how Student::display() calls Person::display() to reuse the base class functionality before adding its own details.

Inheritance is powerful for several reasons:

1. Code Reusability: Instead of rewriting common functionalities, you can inherit them from a base class, making maintenance easier and reducing errors.
2. Extension: You can extend existing code by adding new features to a derived class without changing the existing base class.
3. Hierarchy: It helps in organizing code in a hierarchical manner, which reflects real-world relationships and improves code readability and structure.

Inheritance is a cornerstone of OOP, and understanding it will enable you to design more flexible and scalable applications. It's an essential concept for mastering OOP.

Excited to start practicing? Let's move on and put this theory into action!