PHP lesson 16: Your own functions and return

UK version. UK school years and UK spelling. · US version of this lesson

A function is a named block of code you can run again and again: function greet() { echo "Hi!"; } then greet();. Functions make programs shorter and easier to test. A complete 40-minute PHP lesson (Years 10–11, KS4), from Unit 6: Functions. It runs right here in your browser – nothing to install.

Time: 40 minutes + 20 min homework
Year: Years 10–11, KS4 (ages 14–18)
You need: A computer or tablet, paper and a pencil
Marked: 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 – marked 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: Why is a function that returns its answer more useful than one that prints it?

Watch out for

return prints the value. Only echo prints; return hands it back.
A function runs when it is defined. It runs only when it is called.

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

We are learning to define a function with function name() { }.

Success looks like

I can define a function with function name() { }.
I can give back a value with return.
I can tell return from echo.

Key words

function · define · call · return · reuse

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)

A function is a named block of code you can run again and again: function greet() { echo "Hi!"; } then greet();. Functions make programs shorter and easier to test.

return hands a value BACK to the code that called the function: function double($n) { return $n * 2; } then echo double(4); prints 8. return also ends the function at once.

A function with no return gives back null. A common bug: a function that echoes its answer instead of returning it can't be used in a sum like double(4) + 1.

Worked example – see it

<?php
function double($n) {
    return $n * 2;
}
echo double(6);

It prints:

The lesson, step by step

40 minutes in 5 parts
Part	Time	How it is checked
Starter	5 min	Marked by Classfern
Teaching input	8 min	Read, watch and talk
See it, then predict	8 min	Marked by Classfern
Put it in order, trace it, check it	14 min	Marked by Classfern
Plenary and exit ticket	5 min	Marked 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 marked instantly.

Write it and fix it: practice tests

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

All PHP practice tests · All 24 PHP lessons

Curriculum

National curriculum in England, computing, key stage 4: pupils should be taught to develop and apply their analytic, problem-solving, design, and computational thinking skills.

Contains public sector information licensed under the Open Government Licence v3.0.

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.