Booleans
Very often, in programming, you will need a data type that can only have one of two values, like:
- YES / NO
- ON / OFF
- TRUE / FALSE
For this, Rust has a bool data type, which is known as booleans.
Booleans represent values that are either true or false .
Creating Boolean Variables
You can store a boolean value in a variable using the bool type:
Example
let is_programming_fun: bool = true;
let is_fish_tasty: bool = false;
println!("Is Programming Fun? {}", is_programming_fun);
println!("Is Fish Tasty? {}", is_fish_tasty);Remember that Rust is smart enough to understand that true and false values are boolean values, meaning that you don't have to specify the bool keyword:
Example
let is_programming_fun = true;
let is_fish_tasty = false;
println!("Is Programming Fun? {}", is_programming_fun);
println!("Is Fish Tasty? {}", is_fish_tasty);Boolean from Comparison
Most of the time, there is no need to type true or false yourself. Instead, boolean values come from comparing values using operators like == or > :
Example
let age = 20;
let can_vote = age >= 18;
println!("Can vote? {}", can_vote);Here, age >= 18 returns true , as long as age is 18 or older.
Using Booleans in if Statements
Boolean values are often used in if statements to decide what code should run:
Example
let is_logged_in = true;
if is_logged_in {
println!("Welcome back!");
} else {
println!("Please log in.");
}Cool, right? Booleans are the basis for all Rust comparisons and conditions. You will learn more about if and else statements in the next chapter.