Defining classes

Learn to define classes with the class keyword.

Defining a class

A class is a template used to create objects. In C++ a class starts with the class keyword, followed by a name and a body in curly braces. A semicolon is required after the body.

Example: class Book { };. Here Book is the class name; the body is empty for now. Class names use PascalCase: UserAccount, ShoppingCart. Defining a class does not run it; it only prepares the template. To use the template you declare a variable to create an instance.

Creating instances

To create an object from a class you declare a variable. The simplest way in C++ is stack allocation: Book book;. This line allocates a Book object in memory and binds the book variable to it.

You can also give an initial value with braces: Book book{ };. You access the instance's members later with a dot: book.title. Here book is the object itself, not a reference.

Exercise Define the Book class and create an instance

Define a Book class with an empty body. Inside main create an instance with Book book; and print "Book created" with std::cout.

Show example solution

#include <iostream>

class Book {
};

int main() {
    Book book;
    std::cout << "Book created";
    return 0;
}

Test yourself

Which is a valid class definition?
- Book class { }
- function Book() { }
- class Book()
- class Book { };
Show answer

class Book { }; — The class keyword comes first, then the name, braces and a semicolon.
Complete the class definition
```
____ Book { };
```
Show answer
```
class Book { };
```
Match each keyword to its meaning

class

Class template
new

Instance on the heap
void

No return value
public

Access from anywhere

Next lesson: Member variables

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