What are PHP's variable types?

Question

IT Interview Practice · Accepted Answer

PHP is **dynamically typed** — variables (prefixed with `$`) don't declare a type and can hold any value. PHP has several built-in types covering scalars, compound types, and special values.

## Variables and the scalar types

```php
<?php
$count = 42;          // int
$price = 9.99;        // float
$name = "Ann";        // string
$active = true;       // bool

$count = "now a string";   // dynamically typed — the same variable can change type
```

Variables always start with `$` and infer their type from the assigned value. The four scalar types are `int`, `float`, `string`, `bool`.

## Compound and special types

```php
$list = [1, 2, 3];               // array (PHP's all-purpose collection)
$map = ["name" => "Ann"];        // associative array (key → value)
$obj = new User();                // object (instance of a class)
$fn = fn($x) => $x * 2;           // callable (closure/function)
$nothing = null;                  // null — "no value"
```

Arrays are PHP's versatile collection type (both indexed lists and key-value maps), and there are objects, callables, and `null`.

## Checking and converting types

```php
gettype($count);        // "integer"
is_int($count);          // true
is_string($name);        // true

(int) "42";              // 42 — explicit cast
(string) 42;             // "42"
intval("42px");          // 42
```

## Type juggling — a common gotcha

```php
// PHP automatically converts types in operations ("type juggling")
"5" + 3;        // 8  (string "5" coerced to int)
"5" . 3;         // "53" (. concatenates → both become strings)

// loose vs strict comparison
0 == "hello";    // historically true in old PHP (now false in PHP 8) — type juggling traps
0 === "0";       // false — STRICT comparison checks type too (preferred!)
"1" == 1;        // true (loose) — but "1" === 1 is false
```

PHP's automatic **type juggling** causes surprising comparisons. The fix: prefer **strict comparison (`===`)** which checks type and value, avoiding the loose-comparison (`==`) pitfalls.

## Why it matters

Understanding PHP's variable types is fundamental everyday knowledge.

The key points: PHP is dynamically typed (variables hold any value, types inferred from assignment), with scalar types, the versatile **array** (serving as both list and map — PHP's most-used data structure), objects, and null.

Most importantly, knowing about **type juggling** — PHP's automatic type conversion in operations and comparisons, which causes notorious surprising results — and the practice of using **strict comparison (`===`)** over loose (`==`) to avoid those traps is essential for writing correct, bug-free PHP.

The distinction between `+` (numeric) and `.` (string concatenation), and explicit casting, are also daily basics.

This foundational type knowledge underpins correct PHP code and helps avoid the language's well-known comparison pitfalls.

Variables and the scalar types

Compound and special types

Checking and converting types

Type juggling — a common gotcha

Why it matters

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