C# LanguageComments and regions

Comments

Using comments in your projects is a handy way of leaving explanations of your design choices, and should aim to make your (or someone else's) life easier when maintaining or adding to the code.

There are a two ways of adding a comment to your code.

Single line comments

Any text placed after // will be treated as a comment.

public class Program
{
    // This is the entry point of my program.
    public static void Main()
    {
        // Prints a message to the console. - This is a comment!
        System.Console.WriteLine("Hello, World!"); 

        // System.Console.WriteLine("Hello, World again!"); // You can even comment out code.
        System.Console.ReadLine();
    }
}

Multi line or delimited comments

Any text between /* and */ will be treated as a comment.

public class Program
{
    public static void Main()
    {
        /*
            This is a multi line comment
            it will be ignored by the compiler.
        */
        System.Console.WriteLine("Hello, World!");

        // It's also possible to make an inline comment with /* */
        // although it's rarely used in practice
        System.Console.WriteLine(/* Inline comment */ "Hello, World!");
  
        System.Console.ReadLine();
    }
}

Regions

A region is a collapsible block of code, that can help with the readability and organisation of your code.

NOTE: StyleCop's rule SA1124 DoNotUseRegions discourages use of regions. They are usually a sign of badly organized code, as C# includes partial classes and other features which make regions obsolete.

You can use regions in the following way:

class Program
{
    #region Application entry point
    static void Main(string[] args)
    {
        PrintHelloWorld();
        System.Console.ReadLine();
    }
    #endregion

    #region My method
    private static void PrintHelloWorld()
    {
        System.Console.WriteLine("Hello, World!");
    }
    #endregion
}

When the above code is view in an IDE, you will be able to collapse and expand the code using the + and - symbols.

Expanded

The above code in Visual Studio

Collapsed

The above code in Visual Studio Collapsed using regions

Documentation comments

XML documentation comments can be used to provide API documentation that can be easily processed by tools:

/// <summary>
/// A helper class for validating method arguments.
/// </summary>
public static class Precondition
{
    /// <summary>
    ///     Throws an <see cref="ArgumentOutOfRangeException"/> with the parameter
    ///     name set to <c>paramName</c> if <c>value</c> does not satisfy the 
    ///     <c>predicate</c> specified.
    /// </summary>
    /// <typeparam name="T">
    ///     The type of the argument checked
    /// </typeparam>
    /// <param name="value">
    ///     The argument to be checked
    /// </param>
    /// <param name="predicate">
    ///     The predicate the value is required to satisfy
    /// </param>
    /// <param name="paramName">
    ///     The parameter name to be passed to the
    ///     <see cref="ArgumentOutOfRangeException"/>.
    /// </param>
    /// <returns>The value specified</returns>
    public static T Satisfies<T>(T value, Func<T, bool> predicate, string paramName)
    {
        if (!predicate(value))
            throw new ArgumentOutOfRangeException(paramName);

        return value;
    }
}

Documentation is instantly picked up by IntelliSense:

IntelliSense displaying method documentation