Working with Data Types in PHP

Data Types

PHP is a dynamically typed language, meaning you don’t need to declare variable types explicitly. PHP determines the type based on the value assigned.

Scalar Types

String

Sequences of characters enclosed in quotes.

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$single = 'Hello World';
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$double = "Hello World";
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$name = "John";
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$greeting = "Hello, $name!";  // Variable interpolation (double quotes only)
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// Heredoc for multi-line strings
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$html = <<<HTML
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<div>
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    <h1>Welcome, $name!</h1>
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</div>
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HTML;

Integer

Whole numbers (positive or negative).

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$positive = 42;
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$negative = -17;
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$octal = 0755;        // Octal
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$hex = 0xFF;          // Hexadecimal
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$binary = 0b1010;     // Binary

Float

Numbers with decimal points.

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$price = 19.99;
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$scientific = 1.2e3;  // 1200

Boolean

True or false values.

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$isActive = true;
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$isComplete = false;
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// These values evaluate to false:
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// 0, 0.0, "", "0", null, []

Compound Types

Array

Collections of values.

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// Indexed array
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$colors = ["red", "green", "blue"];
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// Associative array
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$person = [
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    "name" => "John",
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    "age" => 30,
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    "city" => "New York"
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];

Object

Instances of classes.

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class Person {
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    public $name;
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    public $age;
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    public function __construct($name, $age) {
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        $this->name = $name;
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        $this->age = $age;
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    }
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}
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$person = new Person("John", 30);

Special Types

NULL

Represents no value.

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$empty = null;
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// A variable becomes null when:
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unset($someVariable);  // Explicitly unset

Resource

References to external resources like files or database connections.

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$file = fopen("data.txt", "r");
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$db = mysqli_connect("localhost", "user", "pass", "db");

Type Checking

Getting Variable Type

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$value = "Hello";
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gettype($value);     // "string"
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var_dump($value);    // string(5) "Hello"

Type Checking Functions

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is_string($value);   // true
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is_int($value);      // false
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is_array($value);    // false
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is_null($value);     // false
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is_numeric("123");   // true

Checking if Variable Exists

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$name = "John";
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isset($name);        // true - exists and not null
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isset($undefined);   // false
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empty($name);        // false
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empty("");           // true

Type Conversion

Type Juggling (Implicit)

Type juggling (also called type coercion) happens when PHP automatically converts a value from one type to another during an operation. For example, if you add a number to a string that looks like a number, PHP converts the string to a number first, then performs the addition. This happens behind the scenes without you writing any conversion code.

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// String to number
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$str = "123";
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$result = $str + 10;      // 133 (integer)
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$price = "19.99 dollars";
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$tax = $price * 0.1;      // 1.999 (float, reads leading number)
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$text = "hello";
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$result = $text + 5;      // 5 (non-numeric string becomes 0)
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// Number to string
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$number = 123;
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$string = $number . " items";  // "123 items"
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// Boolean context
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if ("0") { }    // false - string "0" is falsy
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if ("hello") { }  // true

Type Casting (Explicit)

Cast Operators

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$value = "123.45";
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(int)$value;       // 123
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(float)$value;     // 123.45
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(string)123;       // "123"
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(bool)$value;      // true
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(array)$value;     // ["123.45"]

Conversion Functions

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$value = "123.45";
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intval($value);    // 123
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floatval($value);  // 123.45
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strval(123);       // "123"
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boolval($value);   // true

Object to Array

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$obj = new stdClass();
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$obj->name = "John";
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$array = (array)$obj;  // ["name" => "John"]

Safe Type Conversion

When dealing with user input, validate before converting.

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function safeIntConvert($value, $default = 0) {
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    if (is_numeric($value)) {
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        return (int)$value;
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    }
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    return $default;
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}
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$userInput = "abc123";
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$number = safeIntConvert($userInput, 0);  // Returns 0