meet it

A loop keeps going while something is `true`.

A while loop is like an if that keeps coming back. It checks its condition, runs its block, then checks again. It stops the first time the condition is false.

Often a keeps track: a number box that changes each turn, like cookies = cookies - 1;. When it runs out, the condition turns false and the loop ends.

Forget to change the counter and the condition stays true forever. That is an : the program never finishes. Make sure something in the block moves it towards the end.

public class Main {
    public static void main(String[] args) {
        int cookies = 3;
        while (cookies > 0) {
            cookies = cookies - 1;
            System.out.println("Nom! Cookies left: " + cookies);
        }
        System.out.println("All gone!");
    }
}

cookies-- takes one away, the same way cookies++ adds one.

guess first

Counting down. What will this show?

Guess before you run it. Wrong guesses are how you learn, and nothing is marked.

public class Main {
    public static void main(String[] args) {
        int count = 3;
        while (count > 0) {
            System.out.println(count);
            count = count - 1;
        }
        System.out.println("Blast off!");
    }
}

your turn

Your turn. Run a countdown.

Choose a whole number to count down from on line 3, then type what happens at the end on line 8. Press run.

Your code

output

press run to see what happens

fix it

The trampoline will not start. Can you fix it?

Broken code to fix

output

press run to see what happens

Java cannot find jumps. Where is that box made?
A counter needs a box with a starting value before the loop can check it.
Add int jumps = 0; as a new line above the while, then press run.

nailed it

your loops know when to stop. :D

A while loop repeats while its condition is true.
Change the counter inside the block so the loop can end.
A condition that never turns false makes an infinite loop.

new words in your collection

while
counter
infinite loop

This lesson isn’t saved. A free account remembers every lesson you finish.

A while loop keeps going while something is true.

Counting down. What will this show?

Your turn. Run a countdown.

The trampoline will not start. Can you fix it?

your loops know when to stop. :D

A loop keeps going while something is `true`.