Ticket Total

Arithmetic and joining text

PHP does ordinary arithmetic with four operators: + for addition, - for subtraction, * for multiplication, and / for division. They work the way you'd expect on numbers stored in variables, not just on numbers typed directly into the code, and the result of a calculation can be stored in a variable of its own before it's used anywhere.

Text is different. To join a piece of text to something else — including a number — PHP uses the dot operator, ., not +. "Total: " . $total builds one string out of two pieces; "Total: " + $total is a type error, because + in PHP is reserved strictly for arithmetic.

A worked example

Here's a different calculation, so you can see the shape of it before touching today's exercise:

<?php
$length = 5;
$width = 4;
$area = $length * $width;
echo "The room is " . $area . " square meters.\n";

Running it prints:

The room is 20 square meters.

$area is computed first, on its own line, and only then joined into a sentence with .. Keeping the calculation and the printing as separate steps makes both of them easier to read — and easier to fix, if one of them turns out to be wrong.

Your turn

The starter program is supposed to multiply a ticket price by a quantity to get a total, then print it. Right now the total comes out too small, because the line that computes it uses the wrong operator.

Read the comment above the calculation — it says what the total is supposed to represent. Compare that to the operator actually used in the line below it, pick the one that matches "multiply," and press Run.

If something goes wrong

If the total is way off, check which operator is doing the calculating — + and * are easy to swap without noticing, especially when you're moving quickly, but PHP has no idea which one you meant; it only does exactly what's written. If PHP reports a type error mentioning "unsupported operand types," look for a + where a . was needed to join a piece of text and a number together instead of adding them.