Course Content

C Preprocessing

1. Introduction to Preprocessing

Introduction to Compilation Stages Role of the Preprocessor Preprocessing Commands

2. Macros

Symbolic Constant Macro With Arguments Advanced Usage of Symbolic Constant Cancel Macro Stringify Operators

3. Conditional compilation

Fundamentals of Conditional Compilation Core Directives Practical Use Cases Pitfalls and Best Practices

Core Directives

main


              12345678910
            
#include <stdio.h>
#define VERSION 2

int main() {
    #if VERSION == 2
        // If VERSION equals 2, this block will be compiled
        printf("Version 2 is active\n");
    #endif
    return 0;
}

Use it when:

To include or exclude a code block based on a compile-time constan;
To create multiple versions of a program depending on platform, version, or configuration.

Why it’s useful:

Eliminates code from the compiled binary entirely;
Useful for portable code: e.g., different behavior for Windows/Linux;
Helps enable/disable debugging or logging code.

main


              1234567891011
            
#include <stdio.h>
#define VERSION 1

int main() {
    #if VERSION == 2
        printf("Version 2 is active\n");
    #elif VERSION == 1
        printf("Version 1 is active\n");
    #endif
    return 0;
}

Use it when:

You have multiple exclusive compile-time conditions and want to select one;
You want to avoid nested #if...#else blocks.

Why it’s useful:

Keeps configuration logic clean and readable;
Avoids writing deep nesting with many #if.

main


              12345678910111213
            
#include <stdio.h>
#define VERSION 5

int main() {
    #if VERSION == 1
        printf("Version 1\n");
    #elif VERSION == 2
        printf("Version 2\n");
    #else
        printf("Unknown version\n");
    #endif
    return 0;
}

Use it when:

You want to define a default code path if all previous #if or #elif conditions fail;
Helps ensure one and only one block of code gets compiled.

Why it’s useful:

Guarantees fallbacks are defined;
Makes it easy to handle cases like “if debugging is disabled”.

Use it when:

You started a conditional compilation block — it's mandatory to close it.

Why it’s useful:

Keeps the preprocessor logic valid; -Allows clear structure and grouping.

Let's rewrite the example from the previous section where we implemented logging. Back then, we used the switch...case statement.

Task

Swipe to start coding

Tasks:

To handle each level of logging, use the required conditional compilation directive;
To handle each level of logging, use the required conditional compilation end directive.

Solution

Switch to desktop for real-world practiceContinue from where you are using one of the options below

Everything was clear?

Thanks for your feedback!

Section 3. Chapter 2

Core Directives

main


              12345678910
            
#include <stdio.h>
#define VERSION 2

int main() {
    #if VERSION == 2
        // If VERSION equals 2, this block will be compiled
        printf("Version 2 is active\n");
    #endif
    return 0;
}

Use it when:

To include or exclude a code block based on a compile-time constan;
To create multiple versions of a program depending on platform, version, or configuration.

Why it’s useful:

Eliminates code from the compiled binary entirely;
Useful for portable code: e.g., different behavior for Windows/Linux;
Helps enable/disable debugging or logging code.

main


              1234567891011
            
#include <stdio.h>
#define VERSION 1

int main() {
    #if VERSION == 2
        printf("Version 2 is active\n");
    #elif VERSION == 1
        printf("Version 1 is active\n");
    #endif
    return 0;
}

Use it when:

You have multiple exclusive compile-time conditions and want to select one;
You want to avoid nested #if...#else blocks.

Why it’s useful:

Keeps configuration logic clean and readable;
Avoids writing deep nesting with many #if.

main


              12345678910111213
            
#include <stdio.h>
#define VERSION 5

int main() {
    #if VERSION == 1
        printf("Version 1\n");
    #elif VERSION == 2
        printf("Version 2\n");
    #else
        printf("Unknown version\n");
    #endif
    return 0;
}

Use it when:

You want to define a default code path if all previous #if or #elif conditions fail;
Helps ensure one and only one block of code gets compiled.

Why it’s useful:

Guarantees fallbacks are defined;
Makes it easy to handle cases like “if debugging is disabled”.

Use it when:

You started a conditional compilation block — it's mandatory to close it.

Why it’s useful:

Keeps the preprocessor logic valid; -Allows clear structure and grouping.

Let's rewrite the example from the previous section where we implemented logging. Back then, we used the switch...case statement.

Task

Swipe to start coding

Tasks:

To handle each level of logging, use the required conditional compilation directive;
To handle each level of logging, use the required conditional compilation end directive.

Solution

Switch to desktop for real-world practiceContinue from where you are using one of the options below

Everything was clear?

Thanks for your feedback!

Section 3. Chapter 2

Switch to desktop for real-world practiceContinue from where you are using one of the options below