PHP lesson 2: Variables, types and var_dump()

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

A variable is a named box for a value. In PHP every variable name starts with a dollar sign: $score = 10;. Names are case-sensitive, so $Score is a different box. A complete 40-minute PHP lesson (Grades 9–12), from Unit 1: Getting started with PHP. 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 one variable of each type and say what var_dump() would show for it.

Watch out for

$score and $Score are the same variable. Variable names are case-sensitive in PHP.
"7" and 7 are the same thing. var_dump("7") says string(1) "7"; var_dump(7) says int(7).

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: store values in variables that start with $.

Success looks like

I can store values in variables that start with $.
I can name the types int, float, string, bool and null.
I can use var_dump() to see a value and its type.

Key words

variable · assignment · int · float · string · bool · null · var_dump

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 variable is a named box for a value. In PHP every variable name starts with a dollar sign: $score = 10;. Names are case-sensitive, so $Score is a different box.

PHP has types: whole numbers (int, like 7), decimals (float, like 2.5), text (string, like "cat"), true/false (bool) and null (nothing). PHP works the type out from the value you store.

var_dump($x) shows the type and the value, like int(7) or string(3) "cat" – the number in brackets is how many characters. It is the best tool for seeing what is really inside a variable.

Worked example – see it

<?php
$total = 5;
echo $total;

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): 2-AP-11 – Create clearly named variables of different data types and operate on them; 3A-AP-13 – Prototype algorithms for problems drawing on prior knowledge and interests.

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.