The user-defined data types are

Array
Objects

Array

An array is formally defined as an indexed collection of data values. Each index (also known as the key) of an array is unique and references a corresponding value.

Example :

 <!DOCTYPE html>
<html lang="en">
<head>
    <title>PHP Arrays</title>
</head>
<body>

<?php
$colors = array("Red", "Green", "Blue");
var_dump($colors);
echo "<br>";
 
$color_codes = array(
    "Red" => "#ff0000",
    "Green" => "#00ff00",
    "Blue" => "#0000ff"
);
var_dump($color_codes);
?>

</body>
</html>

Output:-

array(3) { [0]=> string(3) "Red" [1]=> string(5) "Green" [2]=> string(4) "Blue" }
array(3) { ["Red"]=> string(7) "#ff0000" ["Green"]=> string(7) "#00ff00" ["Blue"]=> string(7) "#0000ff"

Objects

An Object is an individual instance of the data structure defined by a class. We define a class once and then make many objects that belong to it. Objects are also known as instances

Example :

 
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Car Information</title>
</head>
<body>

<?php

// Define a simple class
class Car {
    // Properties
    public $brand;
    public $model;

    // Constructor
    public function __construct($brand, $model) {
        $this->brand = $brand;
        $this->model = $model;
    }

    // Method
    public function startEngine() {
        return "Engine started for {$this->brand} {$this->model}.";
    }
}

// Instantiate objects based on the class
$car1 = new Car("Toyota", "Camry");
$car2 = new Car("Ford", "Mustang");

// Access and manipulate object properties
$car1->brand = "Honda";

// Call object methods
$message1 = $car1->startEngine();
$message2 = $car2->startEngine();
?>

<!-- Display the output within the HTML structure -->
<h1>Car Information</h1>

<p><?php echo $message1; ?></p>
<p><?php echo $message2; ?></p>

</body>
</html>

Output :-

Car Information
Engine started for Honda Camry.
Engine started for Ford Mustang.

The special data types are

NULL
Resource

Null

In PHP, NULL is a special constant that represents the absence of a value or an uninitialized variable. It is a data type on its own and is used to indicate that a variable has no assigned value.

Example :

 
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>NULL</title>
</head>
<body>

<?php
$name = NULL;
if ($name === NULL) {
    echo '<p> variable is NULL.</p>';
}
?>

</body>
</html>

Output:

variable is NULL.

Resource

A resource in PHP is a special data type that represents a handle to external entities, such as files, database connections, network sockets, and more. Resources are typically created and manipulated by functions provided by PHP extensions or external libraries.

Example :-

 <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>File Handling Example</title>
</head>
<body>

<?php

// Open a file and get a file handle resource
$fileHandle = fopen('example.txt', 'r');

// Check if the variable is a resource
if (is_resource($fileHandle)) {
    echo '<p>File handle is a resource.</p>';

    // Read content from the file
    $content = fread($fileHandle, filesize('example.txt'));
    echo '<p>File content: ' . $content . '</p>';

    // Close the file handle to release the resource
    fclose($fileHandle);
} else {
    echo '<p>Not a valid resource.</p>';
}

?>

</body>
</html>

Output :- 

Not a valid resource.

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