#include

The #include directive in C++ is used to include header files in our program.

When we include a header file, the contents of that header file are copied and pasted into our program at the location where the #include directive is written. This allows us to use the declarations and definitions present in the included header file.

The syntax for using #include directive is as follows:

#include <header_file_name>

Here, header_file_name refers to the name of the header file we want to include in our program. We enclose the header file name within angle brackets < > if it is a system header file, or within double quotes " " if it is a user-defined header file.

For example, let's say we want to include the header file iostream in our program. We can do so by writing:

#include <iostream>

This allows us to use the declarations and definitions present in the iostream header file, such as cout and cin.

Including the necessary header files is an important step in C++ programming as it provides access to various predefined functions and classes that we can use in our program.