PHP — Data Types

Eight data types

PHP has eight data types, grouped into three categories:

Category	Types
Scalar	int, float, string, bool
Compound	array, object
Special	resource, NULL

Integer

Whole numbers without a decimal point:

<?php
$a = 42;
$b = -100;
$c = 0;
$d = 1_000_000; // Underscores for readability (PHP 7.4+)

echo gettype($a); // integer
?>

Integers are stored as 64-bit values on most platforms, supporting values up to about 9 quintillion.

Float

Numbers with a decimal point (also called doubles):

<?php
$pi = 3.14159;
$scientific = 1.5e10; // 15,000,000,000
$hex = 0x1A;          // 26 (PHP auto-converts)

echo gettype($pi); // double
?>

Warning: Floats can be imprecise due to binary representation:

<?php
echo 0.1 + 0.2; // 0.30000000000000004

// For exact decimals, use:
echo bcadd("0.1", "0.2", 10); // 0.3
?>

String

Text enclosed in single or double quotes:

<?php
$single = 'Hello, world!';        // Single-quoted (literal)
$double = "Hello, world!";         // Double-quoted (interpolation)
$backtick = `ls -la`;             // Execution operator (runs command)

echo "My name is $single";        // Interpolation works in double quotes
echo 'My name is $single';        // Literal: My name is $single
?>

Escape sequences in double-quoted strings:

<?php
echo "Line 1\nLine 2";    // Newline
echo "Tab\there";          // Tab
echo "Quote: \"Hi\"";      // Escaped quotes
echo "Backslash: \\";      // Escaped backslash
?>

Boolean

true or false:

<?php
$isActive = true;
$isDeleted = false;

// Many values are "falsy" in PHP:
// false, 0, 0.0, "", "0", null, empty array, empty object

var_dump((bool) 0);     // false
var_dump((bool) 1);     // true
var_dump((bool) "");    // false
var_dump((bool) "abc"); // true
?>

Array

An ordered map of key-value pairs:

<?php
// Indexed array
$fruits = ["Apple", "Banana", "Cherry"];
echo $fruits[0]; // Apple

// Associative array
$person = [
    "name" => "Alice",
    "age" => 30,
    "email" => "alice@example.com"
];
echo $person["name"]; // Alice

// Mixed
$mixed = [1, "two", 3.0, true];
?>

Object

An instance of a class:

<?php
class Person {
    public string $name;
    public int $age;

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

    public function greet(): string {
        return "Hi, I'm {$this->name}!";
    }
}

$alice = new Person("Alice", 30);
echo $alice->greet(); // Hi, I'm Alice!
echo gettype($alice); // object
?>

NULL

The absence of a value:

<?php
$var = null;       // Explicit NULL
$other = unset($var); // unset returns void

var_dump($var);    // NULL

// NULL is falsy
if (!$var) {
    echo "This variable is NULL";
}

// isset() returns false for NULL
echo isset($var);  // 0 (false)
echo is_null($var); // 1 (true)
?>

Resource

A reference to an external resource (file, database connection, etc.):

<?php
$file = fopen("example.txt", "r"); // resource
echo get_resource_id($file);       // Unique ID
fclose($file);                     // Free the resource
?>

Resources are not created directly — they come from built-in functions like fopen(), mysqli_connect(), or curl_init().

Type casting

Convert between types using explicit casts:

<?php
$x = "42";
$y = (int) $x;      // 42 (integer)
$z = (float) $x;    // 42.0 (float)
$b = (bool) $x;     // true (non-empty string)

echo gettype($y);   // integer
echo gettype($z);   // double
echo gettype($b);   // boolean
?>

PHP also provides safe casting functions:

<?php
intval("123abc");    // 123
floatval("3.14abc"); // 3.14
strval(42);          // "42"
boolval(0);          // false
settype($var, "int"); // Convert in place
?>

Type checking functions

Function	Returns true if
is_int($v)	Value is an integer
is_float($v)	Value is a float
is_string($v)	Value is a string
is_bool($v)	Value is a boolean
is_array($v)	Value is an array
is_object($v)	Value is an object
is_null($v)	Value is NULL
is_resource($v)	Value is a resource

Mini Practice

Write PHP code that:

1. Creates variables of each scalar type and prints their types
2. Demonstrates the difference between single and double quoted strings
3. Creates an associative array and accesses its values
4. Uses type casting to convert a string to an integer and a float

Up Next

In the next lesson, you'll learn about Strings — formatting, manipulation, and common string functions.