Why are classes (in C++) useful?

Classes in C++ are useful for several reasons:

1. Encapsulation: Classes allow us to bundle data and methods that operate on that data within one single unit. This is known as encapsulation. It helps to keep the data safe from outside interference and misuse.

2. Data Abstraction: Classes provide a way to abstract data. They can hide the complex details of how data is stored and manipulated from the user, allowing them to focus on solving the problem at hand.

3. Inheritance: Classes allow for inheritance, a key feature of object-oriented programming. This means that you can create a new class that inherits the properties and methods of an existing class. This promotes code reusability and logical structure.

4. Polymorphism: Classes also allow for polymorphism, another key feature of object-oriented programming. This means that a single function or operator can behave differently depending on the type of its arguments. This makes the code more flexible and easier to maintain.

5. Modularity: By using classes, you can create more modular code. Each class has a specific task. If a change is required, you would only need to update the relevant class. This makes the code easier to maintain and understand.

6. Code Organization: Classes help in organizing code in a clean and efficient way. It's easier to navigate and understand the code when it's divided into classes.

In summary, classes in C++ provide a structure that not only makes the code more efficient and easier to manage, but also helps in creating real-world models.