Comments

Goal of This Episode

Learn to write notes (comments) inside your code, so you and others can tell what you’re doing.

Main Text

When writing code, sometimes you’ll want to jot a note beside it, reminding yourself “here’s what this part does.” That’s what comments are for.

Comments are never executed by the computer — they exist purely for humans to read.

Single-line Comments

Start with //, and the rest of the line becomes a comment:

fn main() {
    // This is a comment; the computer ignores this line
    let x = 5; // You can also put one after code
    println!("{}", x);
}

Running this still prints just 5 — those two comments have no effect on the program at all.

Multi-line Comments

If you want to write a longer note, you can wrap it in /* */:

fn main() {
    /*
        This is a multi-line comment
        It can span several lines
        The computer ignores all of it
    */
    let x = 10;
    println!("{}", x);
}

When Should You Write Comments?

• When the logic of a piece of code isn’t obvious.
• When you’re worried you’ll forget what it does when you come back a few days later.
• When you want to temporarily stop a line of code from running (i.e., “comment it out”).

fn main() {
    let x = 5;
    // println!("{}", x); // Not printing for now, but don't want to delete it
    println!("Program finished");
}

Now println!("{}", x); won’t be executed, but you can bring it back to life at any time by removing the //.

A Small Reminder

You don’t need a comment on every line! Good code should be clear enough on its own. Comments are for the “non-obvious” spots — not for explaining every single line.

Recap

• // is a single-line comment; /* */ is a multi-line comment.
• Comments are for humans; the computer ignores them completely.
• You can use comments to temporarily “switch off” a line of code without deleting it.
• Good code should be clear on its own; save comments for the non-obvious parts.