Lecture
This lecture introduces abstract classes and pure virtual methods in C++. It covers the need for pure virtual methods, examples of their implementation, and the syntax for defining them. The instructor explains how abstract classes cannot be instantiated and how subclasses must provide definitions for all inherited pure virtual methods. Various examples are provided to illustrate the concept, including a scenario where forgetting to define a pure virtual method leads to a compilation error. The lecture also discusses the implementation of pure virtual methods in concrete classes like circles and polygons.