Welcome back! Previously, you delved into polymorphism and learned how to create more flexible code structures using classes and inheritance. In this session, we will take a step further and explore a crucial aspect of Object-Oriented Programming: abstract classes and pure virtual functions.

Abstract classes and pure virtual functions are essential when you want to define a common interface for a group of derived classes. They ensure that derived classes implement specific functions, enabling you to write more robust and scalable programs.

Let's revisit some of the key concepts through the following code example:

In this example, we define an abstract class Shape with two pure virtual functions: area and perimeter. Derived classes such as Circle and implement these functions.

Abstract classes and pure virtual functions offer a way to enforce certain patterns and rules in your code. They allow you to design a system where different types of objects can be treated uniformly while ensuring that specific behaviors are implemented in each derived class.

By mastering abstract classes and pure virtual functions, you'll be able to:

1. Create more organized and readable code: You'll have a clear structure that dictates how certain functions should behave.
2. Encourage code reusability: Common code can reside in abstract base classes, reducing redundancy.
3. Enhance flexibility: Easily add new types of derived classes without modifying existing code — a key principle of software design.

Intrigued? Let's move on to the practice section and solidify these concepts together. You're on your way to becoming proficient in building sophisticated and maintainable systems!