PHP: Variables & Data Types

What you will learn

How to declare variables (they always start with $), PHP's dynamic typing, and the strangeness of loose comparison.

PHP is dynamically typed — a variable can hold a string now and a number later. Variables must start with $ followed by a letter or underscore.

$name = "Alice";    // string
$age = 25;          // int
$height = 5.6;      // float
$isStudent = true;  // bool

Variable naming rules

• Must start with $ then a letter or _
• Case-sensitive: $Name and $name are different
• Convention: $snake_case

Dynamic typing in action

PHP converts types automatically in many contexts:

$result = "5" + 3;   // 8 (string "5" converted to int)
$result = "5" . 3;   // "53" (. is concatenation)

The + operator coerces strings to numbers. The . operator concatenates (coerces numbers to strings).

Loose vs strict comparison

var_dump(5 == "5");   // bool(true)  — loose, coerces types
var_dump(5 === "5");  // bool(false) — strict, checks type too

Use === (identical) to avoid surprises. This is one of PHP's most common gotchas.

Common mistakes

• Forgetting $ at the start of a variable name — PHP will treat it as a constant
• Relying on loose == comparison — "0" == false is true!
• Thinking . is the decimal separator in strings — use . for concatenation, not +

Quick check below!