TopolearnKnowing when PHP converts types for you, and when it doesn't, avoids a whole class of subtle bugs.
Variables start with $ and need no declaration: $count = 3;. A variable's type is whatever value it currently holds. The scalar types are int, float, string and bool, plus null for "no value". Use gettype() or get_debug_type() to inspect a value.
PHP converts types in many operations (type juggling). "5" + 3 is 8 because + is numeric. String concatenation uses ., so "5" . 3 is "53".
Comparison is where juggling bites:
==compares after conversion:"1" == "01"and100 == "1e2"are both true.===compares value and type:"1" === 1is false. Prefer===by default.- Since PHP 8, comparing a number with a non-numeric string compares them as strings, so
0 == "abc"is now false (it was true in PHP 7).
Falsy values are false, 0, 0.0, "", "0", null and empty arrays. Note that "0" is falsy but "0.0" and " " are truthy.
The null coalescing operator ?? gives a default when a value is null or undefined: $name = $input ?? 'guest';. Its assignment form is $x ??= []. Constants are declared with const MAX = 10; or define('MAX', 10); and are written without $.
Example
<?php
$count = 3;
$price = 9.5;
$name = "Ada";
$active = true;
$nothing = null;
echo get_debug_type($price), "\n"; // float
echo "5" + 3, "\n"; // 8
echo "5" . 3, "\n"; // 53
var_dump("1" == "01"); // bool(true)
var_dump("1" === 1); // bool(false)
var_dump(0 == "abc"); // bool(false) since PHP 8
$user = $nothing ?? "guest";
echo $user, "\n"; // guest
const MAX_ITEMS = 10;
echo MAX_ITEMS * 2, "\n"; // 20Remember
- Variables start with $ and take the type of their current value
- Use === unless you really want type juggling
- ?? supplies a default for null or missing values
Watch out for
- Treating "0" as truthy: it is one of PHP's falsy values.