fn main() {
    // Rust contains a single boolean type: `bool`, represented by the keywords `true` and `false`.
    // Expressions inside `if` and `while` statements must result in type `bool`. There is no
    // automatic conversion to the boolean type.

    let true_value = true;
    if true_value {
        println!("foo is {}.", true_value);
    }

    let false_value = false;
    if !false_value {
        println!("bar is {}.", false_value);
    }
}