PHP lesson 4: Arithmetic: / % ** and intdiv()
US version. US grades and US spelling. · UK version of this lesson
PHP does math like you do: *, / and % before + and -, and brackets first. ** means "to the power of": 2 ** 3 is 8. A complete 40-minute PHP lesson (Grades 9–12), from Unit 2: Numbers and strings. 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: How could you use
%to test whether a number is even?
Watch out for
7 / 2is 3. In PHP/gives 3.5 – useintdiv()for 3.%means percent.%gives the remainder after dividing.
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: use + - * / % ** and know which goes first.
Success looks like
- I can use
+ - * / % **and know which goes first. - I can predict when
/gives a decimal. - I can use
intdiv()and%for whole-number division.
Key words
operator · order of operations · remainder · modulus · intdiv · power
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)
PHP does math like you do: *, / and % before + and -, and brackets first. ** means "to the power of": 2 ** 3 is 8.
Division / gives the exact answer: 7 / 2 is 3.5. When it divides exactly, you get a whole number: 8 / 2 is 4.
intdiv(7, 2) gives the whole-number part, 3, and 7 % 2 gives the remainder, 1. Together they answer "how many groups, and how many left over?" Dividing by zero is a Fatal error (DivisionByZeroError).
Worked example – see it
<?php echo (4 + 5) * 5;
It prints:
45
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): 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.