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[rustc.git] / src / doc / book / src / ch03-04-comments.md

## Comments

All programmers strive to make their code easy to understand, but sometimes
extra explanation is warranted. In these cases, programmers leave notes, or
*comments*, in their source code that the compiler will ignore but people
reading the source code may find useful.

Here’s a simple comment:

```rust
// hello, world
```

In Rust, comments must start with two slashes and continue until the end of the
line. For comments that extend beyond a single line, you’ll need to include
`//` on each line, like this:

```rust
// So we’re doing something complicated here, long enough that we need
// multiple lines of comments to do it! Whew! Hopefully, this comment will
// explain what’s going on.
```

Comments can also be placed at the end of lines containing code:

<span class="filename">Filename: src/main.rs</span>

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

But you’ll more often see them used in this format, with the comment on a
separate line above the code it’s annotating:

<span class="filename">Filename: src/main.rs</span>

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

Rust also has another kind of comment, documentation comments, which we’ll
discuss in the “Publishing a Crate to Crates.io” section of Chapter 14.