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 automatically determines the type based on the value assigned.

A. Scalar Types

1. String

Sequences of characters enclosed in quotes:

$singleQuoted = 'Hello World';
$doubleQuoted = "Hello World";
$name = "John";
$greeting = "Hello, $name!"; // Variable interpolation with double quotes

// Heredoc for multi-line strings
$html = <<<HTML
<div>
    <h1>Welcome, $name!</h1>
</div>
HTML;

2. Integer

Whole numbers (positive or negative):

$positive = 42;
$negative = -17;
$octal = 0755;          // Octal notation
$hexadecimal = 0xFF;    // Hexadecimal notation
$binary = 0b1010;       // Binary notation (PHP 5.4+)

3. Float (Double)

Numbers with decimal points:

$price = 19.99;
$scientific = 1.2e3;    // Scientific notation (1200)
$negative = -3.14;

4. Boolean

True or false values:

$isActive = true;
$isComplete = false;

// Values that evaluate to false
$false1 = 0;           // Integer zero
$false2 = 0.0;         // Float zero
$false3 = "";          // Empty string
$false4 = "0";         // String zero
$false5 = null;        // NULL value
$false6 = array();     // Empty array

B. Compound Types

1. Array

Collection of values:

// Indexed array
$fruits = array("apple", "banana", "orange");
$colors = ["red", "green", "blue"]; // Short syntax (PHP 5.4+)

// Associative array
$person = array(
    "name" => "John",
    "age" => 30,
    "city" => "New York"
);

// Mixed array
$mixed = [
    0 => "first",
    "key" => "value",
    1 => 42
];

2. Object

Instances of classes:

class Person {
    public $name;
    public $age;

    public function __construct($name, $age) {
        $this->name = $name;
        $this->age = $age;
    }
}

$person = new Person("John", 30);

C. Special Types

1. NULL

Represents no value:

$empty = null;
$undefined = NULL; // Case insensitive

// Variables become NULL when:
unset($someVariable);  // Explicitly unset
$notAssigned;          // Never assigned (generates notice)

2. Resource

Special variables holding references to external resources:

$file = fopen("data.txt", "r");  // File resource
$connection = mysqli_connect("localhost", "user", "pass", "db"); // Database resource

Type Checking

Getting Variable Type

$value = "Hello";
echo gettype($value);        // "string"
echo var_dump($value);       // string(5) "Hello"
echo print_r($value, true);  // Hello

// Type checking functions
var_dump(is_string($value));   // bool(true)
var_dump(is_int($value));      // bool(false)
var_dump(is_array($value));    // bool(false)
var_dump(is_null($value));     // bool(false)

Checking if Variable Exists

$name = "John";

var_dump(isset($name));        // bool(true)
var_dump(isset($undefined));   // bool(false)
var_dump(empty($name));        // bool(false)
var_dump(empty(""));           // bool(true)

// Check if variable is set and not null
if (isset($name) && $name !== null) {
    echo "Variable exists and has value";
}

Type Conversion

Type Juggling (Implicit Type Conversion)

PHP automatically converts types when needed in expressions:

String to Number Conversion

$str = "123";
$num = $str + 0;      // $num becomes integer 123
$result = $str * 2;   // $result becomes integer 246

// Leading numeric strings
$price = "19.99 dollars";
$tax = $price * 0.1;  // $tax becomes float 1.999

// Non-numeric strings become 0
$text = "hello";
$result = $text + 5;  // $result becomes integer 5

Number to String Conversion

$number = 123;
$string = $number . " items";  // "123 items"
$concat = "Price: $" . 19.99;  // "Price: $19.99"

Boolean Conversion

// Converting to boolean in conditions
$value = "0";
if ($value) {  // false - string "0" is falsy
    echo "Truthy";
} else {
    echo "Falsy";
}

// Explicit boolean conversion
$bool = (bool)"hello";    // true
$bool = (bool)"";         // false
$bool = (bool)0;          // false
$bool = (bool)1;          // true

Array and Object Juggling

$array = [1, 2, 3];
$count = count($array);   // Integer 3
$string = implode(",", $array); // "1,2,3"

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

Explicit Type Conversion (Type Casting)

Cast Operators

$value = "123.45";

$int = (int)$value;        // 123
$float = (float)$value;    // 123.45
$string = (string)123;     // "123"
$bool = (bool)$value;      // true
$array = (array)$value;    // ["123.45"]
$object = (object)$value;  // stdClass with scalar property

Type Conversion Functions

$value = "123.45";

// Convert to integer
$int1 = intval($value);           // 123
$int2 = (int)$value;              // 123
$int3 = filter_var($value, FILTER_VALIDATE_INT); // false (not pure int)

// Convert to float
$float1 = floatval($value);       // 123.45
$float2 = (float)$value;          // 123.45

// Convert to string
$string1 = strval(123);           // "123"
$string2 = (string)123;           // "123"

// Convert to boolean
$bool1 = boolval($value);         // true
$bool2 = (bool)$value;            // true

Safe Type Conversion

function safeIntConvert($value, $default = 0) {
    if (is_numeric($value)) {
        return (int)$value;
    }
    return $default;
}

$userInput = "abc123";
$number = safeIntConvert($userInput, 0); // Returns 0