PHP lesson 15: Associative arrays: keys and values
US version. US grades and US spelling. · UK version of this lesson
An associative array uses NAMES as keys: $ages = ["Sam" => 15, "Ava" => 16];. $ages["Sam"] is 15. It is like a table with two columns. A complete 40-minute PHP lesson (Grades 9–12), from Unit 5: Arrays. 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: Design an associative array for a school timetable. What are the keys?
Watch out for
- Associative arrays are kept in key order. They keep the order you added them.
- A missing key gives 0. It gives a warning and null.
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: make an associative array of keys and values.
Success looks like
- I can make an associative array of keys and values.
- I can loop over keys and values.
- I can check a key with
isset()orarray_key_exists().
Key words
associative array · key · value · pair · isset · ksort
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)
An associative array uses NAMES as keys: $ages = ["Sam" => 15, "Ava" => 16];. $ages["Sam"] is 15. It is like a table with two columns.
foreach ($ages as $name => $age) visits every pair in the order you added them. PHP does not sort the keys for you; ksort() sorts by key and asort() by value.
Reading a key that doesn't exist gives a Warning ("Undefined array key"). Check first with isset($ages["Max"]), or give a default with $ages["Max"] ?? 0.
Worked example – see it
<?php $ages = ["Zara" => 16, "Amir" => 14, "Max" => 15]; echo count($ages);
It prints:
3
The lesson, step by step
| 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.
Curriculum
CSTA K–12 Computer Science Standards (2017): 3B-AP-12 – Compare and contrast fundamental data structures and their uses; 3A-AP-14 – Use lists to simplify solutions and generalise beyond single variables.
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.