Comments

Comments are notes you leave in your code for yourself and other developers. The compiler ignores them completely — they're purely for human readers. Good comments explain why something is done, not what the code does (the code already shows that).

Single-Line Comments (//)

Two forward slashes comment out everything after them on that line:


// This is a single-line comment
int x = 10;  // You can put comments at the end of a line too

// Console.WriteLine("This won't run");  // Useful for temporarily disabling code

Single-line comments are perfect for quick explanations or temporarily removing a line during debugging.

Multi-Line Comments (/* */)

When you need more than one line, use the /* */ syntax. Everything between the opening and closing markers is commented out:


/* This is a multi-line comment.
   It can span several lines.
   Everything here is ignored by the compiler. */

/*
  This is also useful for commenting out
  large blocks of code during debugging:
int a = 1;
int b = 2;
int c = a + b;
Console.WriteLine(c);
*/

XML Documentation Comments (///)

C# has a special type of comment for documenting classes, methods, and properties. These use three slashes and XML tags:


/// <summary>
/// Calculates the area of a circle given its radius.
/// </summary>
/// <param name="radius">The radius of the circle</param>
/// <returns>The area as a double</returns>
static double CircleArea(double radius) {
  return Math.PI * radius * radius;
}

When you use this style, Visual Studio and VS Code show those descriptions in IntelliSense tooltips. Other developers see your documentation right as they're typing code.

You'll see /// comments in professional codebases and open-source libraries. They're optional but incredibly helpful for public APIs.

Try it Yourself →

When to Comment

Here's my rule of thumb: comment the why, not the what. Reading // Adds 1 to x above x++ is useless — the code already shows that. But // Increment x because the loop tracks attempts tells me the purpose.

And remember: the best comment is often a well-named variable or method. int userAge is clearer than int a with a comment explaining what a is.

← Input & Output

Arithmetic Operators →