Variables and types

2 min read 6 runnable examples Quiz included

PHP variables start with a dollar sign. You don't declare a type; PHP works it out from the value.

PHP

<?php
$name = "Asha";
$age = 21;
$height = 1.65;
$isMember = true;

echo "$name is $age years old\n";
var_dump($name, $age, $height, $isMember);

var_dump() shows a value's type and contents, which makes it the go-to debugging tool in PHP.

Types

Type	Example
`string`	`"hello"`
`int`	`42`
`float`	`3.14`
`bool`	`true`, `false`
`array`	`[1, 2, 3]`
`null`	`null` (no value)

PHP

<?php
echo gettype(42), "\n";
echo gettype("42"), "\n";
echo gettype(4.2), "\n";
echo gettype(null), "\n";

Type juggling

PHP converts types automatically when it thinks it should:

PHP

<?php
var_dump("5" + 3);       // int(8): the string becomes a number
var_dump("5" . 3);       // string "53": . always joins text
var_dump(10 / 4);        // float(2.5)
var_dump(intdiv(10, 4)); // int(2)

Comparing: == versus ===

PHP

<?php
var_dump(5 == "5");      // true: compares values after conversion
var_dump(5 === "5");     // false: compares value AND type
var_dump(0 == "a");      // false in PHP 8
var_dump(null == false); // true

Use === unless you specifically want conversion.

Constants

PHP

<?php
define("SITE_NAME", "CodeMIRAI");
const TAX_RATE = 0.18;
echo SITE_NAME . " charges " . (TAX_RATE * 100) . "% tax\n";

Constants have no $ and can't be changed.

Checking for a value

PHP

<?php
$email = null;
var_dump(isset($email));     // false: null or not set
var_dump(empty(""));         // true: empty-ish values
echo $email ?? "no email", "\n";   // null coalescing: a default

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