How do you define a class in C++?

To define a class in C++, you use the 'class' keyword followed by the class name. This syntax is essential for creating a user-defined data type that can encapsulate data and functions in a single entity. The class definition includes members, which can be variables (attributes) and functions (methods), thereby allowing you to model real-world objects and their behaviors within your program effectively.

This method of defining a class provides the foundation for object-oriented programming, enabling features like encapsulation, inheritance, and polymorphism. For instance, a class can contain both private data members, which are not accessible outside the class, and public methods, which can manipulate or retrieve the values of these data members. This organization helps in managing complex systems by keeping data safe and exposing only necessary functionalities.

In contrast, using the 'struct' keyword is more aligned with creating a lightweight data aggregate, wherein the members are public by default. Declaring member variables and methods separately does not constitute a class definition in C++, as the structure and purpose of both elements must be encapsulated within the class body itself. Finally, the 'define' preprocessor directive is unrelated to class definitions and is used for defining macros, not for creating class structures.