Comments

Learn to write // and /* */ comments in Dart.

Comments

A comment is text the compiler ignores. It is used to leave notes explaining the code. Dart has two kinds of comments.

Use // for a single-line comment; it lasts until the end of the line. Use /* ... */ for a block comment spanning multiple lines.

There are also documentation comments starting with ///; external tools collect them. For now we use // and /* */.

When to write comments

Comments are most valuable to explain why the code is written that way. The code already shows what it does; so avoid useless comments like // multiply a by 2.

Temporarily disabling a line (turning it into a comment) is also common. This is called commenting out.

Adding a comment at the top of the file explaining its purpose helps you recall the context quickly when you return.

Exercise Comment and output

Write a program that has a // comment line and uses print to output Comment did not run. The comment content does not matter; it just needs to exist.

Show example solution

void main() {
  // This line is ignored
  print("Comment did not run");
}

Test yourself

Single-line comment

____ This line is ignored by the compiler

Show answer

// This line is ignored by the compiler

Which marks start a multi-line comment?
- # ... #
- -- ... --
- /* ... */
- // ... //
Show answer

/* ... */ — The other marks are not comments in Dart.
Comment types

//

Single-line comment
/* */

Multi-line comment
///

Documentation comment
print

Prints output

Next lesson: String interpolation

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