else

Goal of This Episode

Use else to make the program do something different when the condition doesn’t hold.

Main Text

When we learned if, the program simply did nothing if the condition didn’t hold. But often we want to say: “If this, do A; otherwise, do B.” That’s what else is for.

Basic Usage

fn main() {
    let x = 2;
    if x > 5 {
        println!("big");
    } else {
        println!("small");
    }
}

x is 2. Is 2 greater than 5? No, so the if block is skipped and the else block runs, printing “small”.

Try a Different Value

Change x to 8:

fn main() {
    let x = 8;
    if x > 5 {
        println!("big");
    } else {
        println!("small");
    }
}

This time it prints “big”, because 8 is greater than 5 — the condition holds, so the if side runs.

In Plain Words

You can think of if...else... as:

If the condition holds, do this; otherwise, do that.

Exactly one side will run — never both, and never neither.

Recap

• else follows an if and handles what to do when the condition doesn’t hold.
• if...else... is an either-or: exactly one side runs, never both and never neither.