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C# course · Beginner · Lesson 4/116

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

Single-line comment

Comments are used to add notes to a program. The compiler ignores them; they produce no output at runtime.

In C# a single-line comment starts with // and runs to the end of the line:

// This is a comment
Console.WriteLine("Hello");

Comments explain code and give hints to other developers (or your future self).

Multi-line comment

For comments that span multiple lines you use /* */. The comment starts with /* and ends with */.

/* This comment
   spans multiple
   lines */
Console.WriteLine("OK");

Multi-line comments are ideal for longer explanations. You cannot nest them; one /* closes with one */.

Exercise Use both comment types

Add a // comment, a /* */ comment to the program and print Welcome! with Console.WriteLine.

Show example solution 
Inside Main add //, /* */ comments and Console.WriteLine("Welcome!");.
Example solution:
using System;

class Program
{
    static void Main()
    {
        // Greeting message
        Console.WriteLine("Welcome!");
        /* Program finished */
    }
}

Test yourself

  1. Comment marker

    ____ This is a comment
    Show answer 
    // This is a comment

  2. Which one is a multi-line comment?

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

    /* Comment */ — Correct! /* */ is the multi-line comment marker in C#.

  3. Match the comment types

    //
    Single-line comment
    /* */
    Multi-line comment
    ///
    XML documentation comment

All lessons in Beginner

1 C# basics

  1. What is C# and .NET?
  2. Your first program
  3. Console.WriteLine
  4. Comments
  5. Compile and run
  6. Summary - C# basics

2 Variables

  1. Declaring variables
  2. The var keyword
  3. Constants
  4. Type inference
  5. Variable scope
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. Char and bool
  4. String basics
  5. Value and reference types
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  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 String basics

  1. Declaring strings
  2. String interpolation
  3. String concatenation
  4. String.Format
  5. Verbatim strings
  6. Summary - String basics

7 Conditionals

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

8 Loops

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

9 Project: Shopping cart

  1. Cart design
  2. Adding products
  3. Calculating totals
  4. Updating quantity
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. Array length
  4. Multidimensional arrays
  5. Jagged arrays
  6. Summary - Arrays

11 Array methods

  1. Array.Sort
  2. Array.Reverse
  3. Array.IndexOf
  4. Array.Copy
  5. Array.Find and FindAll
  6. Summary - Array methods

12 Collections

  1. List<T> basics
  2. List<T> methods
  3. Dictionary<K,V>
  4. Dictionary access
  5. HashSet<T>
  6. Summary - Collections

13 Methods

  1. Defining methods
  2. Return values
  3. void methods
  4. Method overloading
  5. Local functions
  6. Summary - Methods

14 Method parameters

  1. Parameterized methods
  2. Default parameters
  3. The params keyword
  4. ref parameters
  5. out parameters
  6. Summary - Method parameters

15 Project: To-do CLI

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

16 Advanced string methods

  1. Substring
  2. IndexOf and LastIndexOf
  3. Split and Join
  4. Trim and Pad
  5. Replace
  6. Summary - Advanced strings

17 Console I/O

  1. Console.ReadLine
  2. Console.ReadKey
  3. int.Parse and TryParse
  4. double.Parse
  5. Console formatting
  6. Summary - Console I/O

18 Enums

  1. Defining enums
  2. Enum values
  3. Enum casting
  4. Enum.Parse
  5. Flags attribute
  6. Summary - Enums

19 Exception basics

  1. try/catch
  2. finally block
  3. throw
  4. The Exception class
  5. Custom exceptions
  6. Summary - Exception basics

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together