Explore OOP in C++ to write cleaner, modular, and scalable code. Learn classes in C++, data hiding, encapsulation, abstraction, inheritance, and polymorphism in C++.

Become  a C++ Programmer

This module aims to teach us how to write cleaner, more modular, and scalable code in C++ by providing an understanding of OOP in C++. We'll start with the basics of object-oriented programming and build up to advanced concepts such as inheritance, data hiding, and polymorphism. Along the way, we'll explore how each concept applies to C++ and how various C++ features facilitate OOP.

Object-Oriented Programming in C++

## Abstract Class

We can only make derived class's objects to access their functions, and we will never want to instantiate objects of a base class, we call it an `abstract` class. Such a class exists only to act as a parent of derived classes that will be used to instantiate objects.

## How to Write a Pure Virtual Function? 

It may also provide an interface for the class hierarchy by placing at least one pure virtual function in the base class. A pure virtual function is one with the expression `=0` added to the declaration. 

### `=0` Sign

The equal sign `=` here has nothing to do with the assignment, the value 0 is not assigned to anything. The `=0` syntax is simply how we tell the compiler that a virtual function will be pure.

## Overriding Virtual Function

Once you’ve placed a pure virtual function in the base class, you must override it in all the derived classes from which you want to instantiate objects. If a class doesn’t override the pure virtual function, it becomes an abstract class itself, and you can’t instantiate objects from it (although you might from classes derived from it). For consistency, you may want to make all the virtual functions in the base class pure.

# Abstract Class

We can only make derived class's objects to access their functions, and we will never want to instantiate objects of a base class, we call it an `abstract` class. Such a class exists only to act as a parent of derived classes that will be used to instantiate objects.

# How to Write a Pure Virtual Function? 

It may also provide an interface for the class hierarchy by placing at least one pure virtual function in the base class. A pure virtual function is one with the expression `=0` added to the declaration. 

## `=0` Sign

The equal sign `=` here has nothing to do with the assignment, the value 0 is not assigned to anything. The `=0` syntax is simply how we tell the compiler that a virtual function will be pure.

# Overriding Virtual Function

Once you’ve placed a pure virtual function in the base class, you must override it in all the derived classes from which you want to instantiate objects. If a class doesn’t override the pure virtual function, it becomes an abstract class itself, and you can’t instantiate objects from it (although you might from classes derived from it). For consistency, you may want to make all the virtual functions in the base class pure.

In this lesson, we'll be learning about a very important concept of polymorphism, i.e.,  Pure Virtual Member Functions.

Introduction

Classes

Data Hiding

Inheritance

Polymorphism

Conclusion

Pure Virtual Member Functions

Abstract Class

How to Write a Pure Virtual Function?