Comments

Rust uses // for line comments and /* */ for block comments:

// Line comment
/* Block comment */

Multi-line comments require // on each line:

// Multi-line comment
// continues here

Comments can be placed at line end or above code:

fn main() {
    let lucky_number = 7; // I'm feeling lucky today
}

fn main() {
    // I'm feeling lucky today
    let lucky_number = 7;
}

Documentation comments (/// and //!) are covered in Chapter 14.