PHP lesson 17: Parameters, defaults and types

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

Parameters are the inputs of a function: function area($w, $h) { return $w * $h; }. When you call area(3, 4), 3 goes into $w and 4 into $h. A complete 40-minute PHP lesson (Grades 9–12), from Unit 6: Functions. 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: Write the first line of a function that takes a name and an age, with types.

Watch out for

Arguments are matched by name. They are matched by position: first to first.
Types are just comments. PHP checks them: "four" for int stops the program.

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: pass values in through parameters.

Success looks like

I can pass values in through parameters.
I can give a parameter a default value.
I can add type declarations like int and string.

Key words

parameter · argument · default value · type declaration · return type

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)

Parameters are the inputs of a function: function area($w, $h) { return $w * $h; }. When you call area(3, 4), 3 goes into $w and 4 into $h.

A default makes a parameter optional: function greet($name = "friend"). Missing a REQUIRED argument stops the program with an ArgumentCountError.

A type declaration says what kind of value is allowed: function square(int $n): int. PHP converts "4" to 4 for you, but a word like "four" stops the program with a TypeError. Types catch bugs early.

Worked example – see it

<?php
function area($w, $h) {
    return $w * $h;
}
echo area(6, 6);

It prints:

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): 3B-AP-14 – Build solutions from student-created procedures, modules or objects; 3A-AP-18 – Create artifacts using procedures, data+procedure combinations or interrelated programs.

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.