PHP lesson 11: while loops

US version. US grades and US spelling. · UK version of this lesson

while (condition) { … } repeats as long as the condition is true. Use it when you don't know in advance how many passes you need – "keep halving until it is below 1". A complete 40-minute PHP lesson (Grades 9–12), from Unit 4: Loops. It runs right here in your browser – nothing to install.

Time: 40 minutes + 20 min homework
Grade: Grades 9–12 (ages 14–18)
You need: A computer or tablet, paper and a pencil
Graded: Instantly, with explanations

For parents: how to use this lesson

You don't need to know PHP yourself. The lesson explains each step on screen, the way Mr Babbage, our Head of Computing, likes it: a worked example first, then a go for your child. Your child predicts what code prints, traces it and puts it in order – graded straight away – and then writes and fixes real PHP in the practice test, where it runs in the browser.

Read what your child will learn together.
Press Start the lesson below. Sit with your child for the teaching and the worked example (about 16 minutes): ask them to say what each line does.
Let them do the practice on their own, then the write-it and fix-it questions in the practice test. When code goes wrong, PHP's message is a clue – let them read it out and try again before you help.
Finish with the talk question: Give one problem that suits a for loop and one that suits a while loop.

Watch out for

A while loop always runs at least once. If the condition is false at the start, it never runs.
continue stops the loop. continue skips to the next pass; break stops.

Miss Lovelace's tip for home: ask your child to explain one line of their program to you in their own words. If they can explain it, they understand it – and every message from PHP is a clue, not a failure.

What your child will learn

Learning goal: write a while loop that stops.

Success looks like

I can write a while loop that stops.
I can choose between for and while.
I can use break and continue.

Key words

while loop · condition · infinite loop · break · continue

What to have ready

A device with a web browser (PHP runs in the browser – nothing to install)
Paper for tracing
A keyboard helps for typing code (a tablet or phone works too)

The big ideas (for the adult)

while (condition) { … } repeats as long as the condition is true. Use it when you don't know in advance how many passes you need – "keep halving until it is below 1".

Something inside the loop must change the condition, or the loop never ends. Here, an endless loop is stopped after a few seconds.

break stops the loop at once. continue skips the rest of THIS pass and starts the next one.

Worked example – see it

<?php
$n = 5;
while ($n > 0) {
    echo $n, " ";
    $n--;
}

It prints:

5 4 3 2 1

The lesson, step by step

40 minutes in 5 parts
Part	Time	How it is checked
Starter	5 min	Graded by Classfern
Teaching input	8 min	Read, watch and talk
See it, then predict	8 min	Graded by Classfern
Put it in order, trace it, check it	14 min	Graded by Classfern
Closure and exit ticket	5 min	Graded by Classfern + self-check

The lesson

It runs here on the page. No sign-up and no names – progress is kept only in this browser. Each visit picks a new mix of questions.

Homework

20 minutes: 5 questions – predict what code prints, trace it or put it in order, and check the key ideas – then a short reflection. New questions every time, all graded instantly.

Write it and fix it: practice tests

The practice tests run real PHP in your browser: write and fix short programs, graded against hidden tests.

All PHP practice tests · All 24 PHP lessons

Curriculum

CSTA K–12 Computer Science Standards (2017): 3A-AP-15 – Justify choice of control structures (implementation, readability, performance).

The standard codes are CSTA's; the descriptions are our own words.

Our lessons and questions are our own. They are not written or endorsed by any government department, testing agency or exam board. Classfern is not affiliated with or endorsed by The PHP Group. PHP runs here as php-wasm, under its open-source licences.