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Comments

Learn to write single-line (//) and multi-line (/* */) comments in C.

Comments

Comments are text that explains the code and is ignored by the compiler. C has two kinds of comments:

  • Single-line: // this is a comment
  • Multi-line: /* this is also a comment */

Comments make code readable and convey your intent to other developers. Avoid adding misleading explanations.

What are comments for?

Comments serve three main purposes:

  • Explanation: describe complex logic to the reader
  • Documentation: say what functions do and what parameters they take
  • Disabling: temporarily turn off trial code

A good comment explains why, not what. Avoid restating the obvious; well-named code often speaks for itself.

Practice Write a program with a comment

Write a C program: #include <stdio.h>, int main(void), and print Hello with printf. Also add at least one single-line comment starting with //.

Sample solution

main.c
#include <stdio.h>

// Account
int main(void) {
    printf("Hello");
    return 0;
}

Expected output

Hello

Questions and answers

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

1 Single-line comment marker

Question 
____ this is a comment
Answer 
// this is a comment

Explanation: // starts a single-line comment.

2 Multi-line comment syntax?

  • /* Comment */ Correct answer
  • # Comment
  • <!-- Comment -->
  • // Comment

Explanation: /* ... */ is a multi-line comment.

3 Match comment types

Term Meaning
// Single-line
/* */ Multi-line
# Not a comment
Explanation Intent

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