Lesson 02 of 20

8 mins read

Variables, Strict Types & Dynamic Casting

In Plain English

Variables in PHP start with a dollar sign ($) and are dynamically typed by default. Learn strict type enforcement (declare(strict_types=1)), scalar types (int, float, string, bool), compound types (array, object), and explicit type casting.

The Mental Model

"A variable without strict types is like a flexible cardboard box that can hold shoes, books, or water bottles at any time. Adding strict types turns the box into a molded holder that only accepts one precise shape."

Deep Dive: How It Works

Variable Syntax: Always prefixed with $ (e.g. $userId = 101;).

Scalar Types: int, float, string, bool, and special types null and resource.

Explicit Casting: Prefix expressions with (int), (float), (string), (bool), or (array).

Strict Types: declare(strict_types=1); enables strict argument and return type checking across function calls.

Syntax Blueprint

<?php

$name = "Alice";
$age = (int)"28";
$isActive = true;

Declare variables with $, assign literals, and convert types explicitly with (type) casting.

Core Rules to Remember

$ Prefix Requirement: All variables must start with $ followed by a letter or underscore.

Type Juggling: PHP automatically coerces strings to numbers in arithmetic operations ("5" + 10 = 15).

Var Dump Inspection: Use var_dump() to inspect the exact data type, length, and internal value of any variable.

Common Beginner Traps & How to Fix Them

Mistake:Assuming "0" evaluates to true in boolean checks.

Why it happens: In PHP, both "" (empty string) and "0" (string containing zero) evaluate to false in boolean contexts.

How to fix: Use strict comparison ($val === "") or strlen($val) > 0 when checking string input.

Pro Tip: Always declare strict_types=1 at the top of every PHP file in modern applications for robust runtime type safety.

Live Interactive Example

Hit Run Code to see it live

Variable Types and Explicit Type Casting

PHP 8.2 / CLI

Output Console

Click "Run Code" to view the rendered output.

How it works: (int)$rawScore cast the string "95" to 95, and adding float 4.5 produced 99.5.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Cast and Format User Metrics

Declare a variable $rawPrice = "49.99".
Cast $rawPrice to float and store it in $price.
Multiply $price by 2 and print "Total: $" followed by the result.

Sandbox Output

Click "Run & Check" to test your solution.

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