The main tasks of the preprocessor are to perform macro substitutions, link external files, conditional compilation, and perform text substitutions. More precisely, it executes all the directives it finds in the file.

Preprocessing prepares the file for future compilation stages, because, for example, the compiler has no idea what the `#include` directive is.

The `#include` directive is used to include the contents of other files into the source code of a program.

<!DOCTYPE html>
<html lang="ru">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <style>
        .custom-text {
            color: red; 
            font-size: 50px;
        }
    </style>
</head>
<body>
    <p class="custom-text">picture</p>
</body>
</html>

```
#include <stdio.h>  // Include standard header file
#include "file.h" // Including a custom header file
```


Macros in C allow you to define text substitutions. When the preprocessor finds a macro in the code, it replaces its value with the one specified in the `#define` directive.

Wherever `PI` appears in the code, it will be replaced with `3.14159`.

Uses a whole set of commands (`#if`, `#ifdef`, `#ifndef`, `#else`, `#elif`, `#endif`) to include or exclude parts of code based on conditions. This is useful when working with platform-dependent code or for debugging.

In the C programming language, there are **special predefined macros** that are automatically provided by the compiler.

I2luY2x1ZGUgPHN0ZGlvLmg+CgppbnQgbWFpbigpCnsKICAgIHByaW50ZigiTnVtYmVyIG9mIGxpbmU6ICVkXG4iLCBfX0xJTkVfXyk7CiAgICByZXR1cm4gMDsKfQ==

These were the main and most frequently used preprocessor directives. In addition to them, there are many more that we will also consider in this course.

Which preprocessor directive should be used for  including new files?

You will discover the secret of compilation using the console and learn how to compile programs manually. Get to know the preprocessor better and learn how to create your own macros of varying complexity. Take your programming skills to the next level with a set of preprocessor directives that will make your programs more understandable, convenient, and make compilation flexible!

Dive into the compilation process, see how to do compilation yourself using terminal commands.

C Preprocessing

Preprocessing Commands

Inclusion

Macro Definition

Conditional Compilation

Defined Macro