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Summary - Preprocessor

  • C course
  • Beginner
  • Lesson 111/116
  • 5 min

Combine #define, #include and #ifdef to write a configuration header.

Summary - Preprocessor

In this group you learned preprocessor directives. #define defines constants and macros; #include includes headers; #ifdef/#ifndef/#endif perform conditional compilation. Macro functions take parameters; header files are protected with include guards.

#define PI 3.14
#include <stdio.h>
#define SQUARE(x) ((x) * (x))
#ifdef DEBUG
    printf("debug");
#endif

The preprocessor rewrites the code as text before compilation. So it does no type checking; use it carefully. Now you will do an exercise that combines all these directives.

Practice VERSION and PRINT_VERSION macros

Define #define VERSION 3 and #define PRINT_VERSION(v) printf("v%d\n", v). In main call PRINT_VERSION(VERSION).

Starter code

main.c
#include <stdio.h>

// Define VERSION 3 and PRINT_VERSION(v) macros
int main(void) {
    // Call PRINT_VERSION(VERSION)
    return 0;
}

Sample solution

main.c
#define VERSION 3
#define PRINT_VERSION(v) printf("v%d\n", v)
PRINT_VERSION(VERSION);

Expected output

v3

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Match directive to task

Term Meaning
#define Defines a constant
#include Includes a header
#ifdef Conditional compilation
#endif Ends a block

2 What is the best approach for a constant value?

  • An int variable
  • A static variable
  • A #define macro Correct answer
  • An extern variable

Explanation: A #define macro is suitable for constants.

3 Fill in the blank: #include directive

Question 
____ <stdio.h>
Answer 
#include <stdio.h>

Explanation: #include <stdio.h> includes standard I/O.

All lessons in Beginner

1 C basics

  1. What is C?
  2. Your first program
  3. Compile and run
  4. Comments
  5. printf and escapes
  6. Summary - C basics

2 Variables

  1. Declaring variables
  2. Variable assignment
  3. const
  4. Variable scope
  5. typedef
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. char
  4. sizeof
  5. Type conversion
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Menu loop
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Bitwise operators
  6. Summary - Operators

6 I/O

  1. printf formatting
  2. scanf
  3. Multiple inputs
  4. getchar and putchar
  5. puts and fputs
  6. Summary - I/O

7 Conditionals

  1. The if statement
  2. else and else if
  3. The switch statement
  4. The ternary operator
  5. Nested conditionals
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. break and continue
  5. Nested loops
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding products
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. Array size
  4. Multidimensional arrays
  5. Arrays and loops
  6. Summary - Arrays

11 Strings

  1. String basics
  2. String literals
  3. strlen
  4. strcpy and strcat
  5. strcmp
  6. Summary - Strings

12 Functions

  1. Defining functions
  2. Return values
  3. Parameters
  4. Function prototypes
  5. Recursion
  6. Summary - Functions

13 Pointer basics

  1. What is a pointer?
  2. The & address operator
  3. Pointer dereference
  4. NULL
  5. Pointer arithmetic
  6. Summary - Pointer basics

14 Arrays and pointers

  1. Array name as pointer
  2. Pointer to array
  3. Passing arrays to functions
  4. Pointer loop
  5. Multidim array pointer
  6. Summary - Arrays and pointers

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 String functions

  1. strchr
  2. strstr
  3. strtok
  4. sprintf
  5. sscanf
  6. Summary - String functions

17 Structs

  1. Defining structs
  2. Using structs
  3. typedef struct
  4. Array of structs
  5. Nested structs
  6. Summary - Structs

18 Memory and stack

  1. Stack and heap
  2. Automatic storage
  3. malloc
  4. free
  5. calloc and realloc
  6. Summary - Memory and stack

19 Preprocessor

  1. #define
  2. #include
  3. Conditional compilation
  4. Macro functions
  5. Header files
  6. Summary - Preprocessor

20 Beginner final

  1. Project design
  2. Data model
  3. Functions
  4. Memory management
  5. Putting it together