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:

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$singleQuoted = 'Hello World';
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$doubleQuoted = "Hello World";
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$name = "John";
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$greeting = "Hello, $name!"; // Variable interpolation with double quotes
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// Heredoc for multi-line strings
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$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;

2. Integer

Whole numbers (positive or negative):

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

3. Float (Double)

Numbers with decimal points:

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

4. Boolean

True or false values:

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

B. Compound Types

1. Array

Collection of values:

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// Indexed array
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$fruits = array("apple", "banana", "orange");
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$colors = ["red", "green", "blue"]; // Short syntax (PHP 5.4+)
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// Associative array
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$person = array(
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    "name" => "John",
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    "age" => 30,
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    "city" => "New York"
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);
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// Mixed array
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$mixed = [
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    0 => "first",
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    "key" => "value",
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    1 => 42
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];

2. 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);

C. Special Types

1. NULL

Represents no value:

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$empty = null;
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$undefined = NULL; // Case insensitive
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// Variables become NULL when:
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unset($someVariable);  // Explicitly unset
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$notAssigned;          // Never assigned (generates notice)

2. Resource

Special variables holding references to external resources:

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

Type Checking

Getting Variable Type

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$value = "Hello";
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echo gettype($value);        // "string"
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echo var_dump($value);       // string(5) "Hello"
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echo print_r($value, true);  // Hello
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// Type checking functions
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var_dump(is_string($value));   // bool(true)
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var_dump(is_int($value));      // bool(false)
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var_dump(is_array($value));    // bool(false)
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var_dump(is_null($value));     // bool(false)

Checking if Variable Exists

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$name = "John";
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var_dump(isset($name));        // bool(true)
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var_dump(isset($undefined));   // bool(false)
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var_dump(empty($name));        // bool(false)
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var_dump(empty(""));           // bool(true)
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// Check if variable is set and not null
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if (isset($name) && $name !== null) {
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    echo "Variable exists and has value";
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}

Type Conversion

Type Juggling (Implicit Type Conversion)

PHP automatically converts types when needed in expressions:

String to Number Conversion

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$str = "123";
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$num = $str + 0;      // $num becomes integer 123
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$result = $str * 2;   // $result becomes integer 246
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// Leading numeric strings
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$price = "19.99 dollars";
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$tax = $price * 0.1;  // $tax becomes float 1.999
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// Non-numeric strings become 0
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$text = "hello";
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$result = $text + 5;  // $result becomes integer 5

Number to String Conversion

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

Boolean Conversion

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// Converting to boolean in conditions
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$value = "0";
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if ($value) {  // false - string "0" is falsy
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    echo "Truthy";
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} else {
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    echo "Falsy";
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}
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// Explicit boolean conversion
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$bool = (bool)"hello";    // true
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$bool = (bool)"";         // false
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$bool = (bool)0;          // false
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$bool = (bool)1;          // true

Array and Object Juggling

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$array = [1, 2, 3];
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$count = count($array);   // Integer 3
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$string = implode(",", $array); // "1,2,3"
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// Object to array
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$obj = new stdClass();
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$obj->name = "John";
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$array = (array)$obj;     // ["name" => "John"]

Explicit Type Conversion (Type Casting)

Cast Operators

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

Type Conversion Functions

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$value = "123.45";
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// Convert to integer
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$int1 = intval($value);           // 123
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$int2 = (int)$value;              // 123
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$int3 = filter_var($value, FILTER_VALIDATE_INT); // false (not pure int)
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// Convert to float
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$float1 = floatval($value);       // 123.45
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$float2 = (float)$value;          // 123.45
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// Convert to string
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$string1 = strval(123);           // "123"
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$string2 = (string)123;           // "123"
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// Convert to boolean
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$bool1 = boolval($value);         // true
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$bool2 = (bool)$value;            // true

Safe Type Conversion

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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