Compound

5. Array

An array can hold multiple values at once.

$array1 = array("apple", "banana", "cherry");
$array2 = ["apple", "banana", "cherry"];

6. Object

An object is an instance of a class. You create objects from classes.

class Fruit {
   public $name;
   function __construct($name) {
       $this->name = $name;
   }
}
$apple = new Fruit("Apple");

Special Data Types

7. Resource

A resource is a special variable, holding a reference to an external resource, like a file, a database connection, image canvas areas, etc.

$file = fopen("text.txt", "r");

8. NULL

NULL is a special data type that only has one value: NULL.

$nullVar = NULL;

Checking Data Types

You can use various functions to check a variable's data type, like is_int(), is_float(), is_string(), is_bool(), is_array(), is_object(), is_resource(), and is_null().

$var = "Hello, World!";
if(is_string($var)) {
   echo '$var is a string.';
}

Type Casting

You can also convert the data type of variables by type casting.

$int = 1;
$str = (string)$int; // convert integer to string

Type Juggling

PHP is capable of automatically converting a variable from one data type to another, depending on the context in which it is used. This is known as "type juggling".

$var = "3" + 4; // $var becomes integer 7

Data types in PHP allow the language to be quite flexible, but it's crucial to be mindful of the kind of data you're working with to prevent unexpected behavior, especially when dealing with different types of data simultaneously.