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In C++, defining a class is the foundation for creating objects that encapsulate data and functions. To define a class, you use the `class` keyword followed by the name you wish to give your class. This name is used as a blueprint for creating objects and should be meaningful to describe what the class represents. After the name, a pair of curly braces `{}` is used to enclose the body of the class.

Within this body, you'll provide definitions for functions and variables that the class will contain. Remember to close the definition with a semicolon (`;`). This structure sets up a template from which individual objects can be instantiated. Here's an example to illustrate:

• `class Car { /* Class definition goes here */ };`

This simple setup forms the basis for object-oriented programming in C++. It is crucial to keep in mind that a class can have multiple members including functions that define its behaviors and variables that store its state.

Member variables, often referred to as data members, are the variables declared inside a class definition. These variables hold data specific to each object instance of the class. Each object will have its own copy of member variables, assuming they are not defined as static.

When defining member variables, you typically specify an access level or scope. The most common access level is `public`, which allows variables to be directly accessed from outside the class using object instances. Other access levels include `private` and `protected`, which restrict access to within the class itself or derived classes.

Here's a basic example:

• `class Book { public: int pages; float price; };`

In this example, each `Book` object will have its own `pages` and `price` variable. It is essential to understand the scope and accessibility of these variables for effective object-oriented programming in C++.

The `static` keyword in C++ is special as it modifies the behavior of a member variable such that it is shared among all instances of a class. A static member variable retains the same value across all objects. Instead of being tied to a single instance, it is tied to the class itself.

To declare a static member variable, place the `static` keyword before its declaration within the class. Then, remember to initialize it outside the class definition. This dual-location declaration ensures that the static variable is accessible and modifiable at the class level rather than the instance level. Example:

• `class Car { public: static int carCount; };`
• `int Car::carCount = 0;`

The static member `carCount` can be altered using `Car::carCount` without needing an object instance. This is useful for attributes that should maintain a single shared state, such as counting the number of objects created during a program execution.