Variables and Output

Goal of This Episode

Learn to create variables with let, then print them out with println!.

Main Text

Last episode we successfully printed “Hello, Rust!”, but that text was hard-coded into the program. What if we want to be a bit more flexible? That’s where variables come in.

What Is a Variable?

A variable gives a value a name, so you can use that value later by that name.

Let’s see how to use one:

fn main() {
    let x = 5;
    println!("{}", x);
}

Here, let x = 5; binds the name x to the value 5.

Then, in println!("{}", x);, the {} is a placeholder — it means “at this spot, please fill in the value of x.”

Text Variables

A variable name can be bound to more than just a number — it can be bound to text too:

fn main() {
    let name = "Rust";
    println!("Hello, {}!", name);
}

See that? The {} was replaced by the value of name, which is "Rust".

Try changing "Rust" to your own name and see what gets printed!

A let Variable Doesn’t Have to Be Assigned Right Away

When you declare a variable with let, you don’t have to give it a value immediately. You can declare first and assign later:

fn main() {
    let x;
    x = 5;
    println!("{}", x);
}

This is perfectly legal, but you must assign to it exactly once before using it — using it without assigning causes a compile error.

Recap

• let creates a variable.
• Text is wrapped in "double quotes".
• println!("{}", variable) prints out the value of a variable.
• {} is a placeholder that gets replaced by the value that follows.
• A variable declared with let doesn’t have to be assigned right away, but it must be assigned exactly once before use.