while

Goal of This Episode

Rewrite the countdown with a while loop, and compare it to the loop + break version.

Main Text

Last episode we built a countdown with loop + break. Today we’ll learn another kind of loop — while — which makes the same logic cleaner to write.

Rewriting the Countdown with while

fn main() {
    let mut count = 5;
    while count > 0 {
        println!("{}", count);
        count -= 1;
    }
    println!("Liftoff!");
}

Exactly the same result!

Comparing with loop + break

Last episode’s version:

fn main() {
    let mut count = 5;
    loop {
        if count == 0 {
            println!("Liftoff!");
            break;
        }
        println!("{}", count);
        count -= 1;
    }
}

The while version:

fn main() {
    let mut count = 5;
    while count > 0 {
        println!("{}", count);
        count -= 1;
    }
    println!("Liftoff!");
}

See the difference? while merges the “condition check” and the “loop” into one. No need to write your own if and break — just tell while: “As long as this condition holds, keep going.”

while in Plain Words

While the condition holds, keep doing what’s inside the curly braces.

while count > 0 → as long as count is greater than 0, keep running. Once count hits 0, the condition no longer holds, and it stops automatically.

When to Use loop, and When while?

• while: You know whether to continue before the loop iteration starts (check the condition first, then decide whether to run).
• loop + break: You can only decide whether to stop somewhere in the middle of the loop.

Both get the job done — it’s just that while is more concise in many situations.

Recap

• A while loop keeps running as long as the condition holds, and stops automatically when it doesn’t.
• More concise than loop + break; good for when you know whether to continue before each iteration.
• loop + break suits cases where the stopping decision happens mid-loop.