PHP Data Types

What Is a Data Type?

In simple terms: A data type describes what kind of value something is — a whole number, a decimal number, text, true/false, a list, and so on.

Technically: Every value in PHP has a type that determines how it is stored in memory, which operations can be performed on it, and how it behaves when compared or converted. Variables themselves do not have fixed types; the value they hold does.

Why Data Types Matter

The same-looking data behaves differently depending on its type:

<?php
var_dump(10 + 5);       // int(15)       — numeric addition
var_dump("10" . "5");   // string(3) "105" — text joined together
var_dump(7 / 2);        // float(3.5)    — division can produce a decimal
var_dump("abc" == 0);   // bool(false)   — comparison rules depend on types

Understanding types explains why a calculation returns a decimal, why a comparison is true or false, why a function rejects an argument, and why data from forms and databases sometimes behaves unexpectedly.

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PHP's Type Categories

PHP has ten basic value types, grouped into three categories.

Category	Type	Example	Holds
Scalar (single value)	bool	true, false	A truth value
	int	42, -7, 0x1F	Whole numbers
	float	3.14, 1.5e3	Decimal numbers
	string	"Hello", 'PHP'	Text (a sequence of bytes)
Compound (contain other values)	array	[1, 2, 3], ['name' => 'Asha']	Ordered key–value collections
	object	new DateTime()	Instances of classes, with properties and methods
	callable	'strtoupper', fn($x) => $x * 2	Anything that can be called like a function
	iterable	Arrays, generators	Anything usable in foreach
Special	null	null	No value
	resource	fopen('file.txt', 'r')	A handle to an external resource

Strictly speaking, callable and iterable describe capabilities that some values have rather than separate storage types. A callable is often a string, array, or Closure object; an iterable is an array or an object implementing Traversable. They appear in this list because they can be used in type declarations.

For type declarations, PHP also provides mixed (any type), void (function returns nothing), never (function never returns), and static/self for classes. These are covered in the Type Declarations in Functions and Mixed and Never Types lessons.

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Dynamic Typing

PHP is dynamically typed: you never declare a variable's type, and PHP determines it from the assigned value.

<?php
$data = 100;          // int
$data = "one hundred"; // now string
$data = [1, 0, 0];     // now array

Advantages

• Less code to write, and fast prototyping.
• Easy handling of loosely structured data such as form input, which always arrives as strings.

Disadvantages

• Type-related bugs appear only when the code runs.
• PHP sometimes converts types automatically (type juggling), which can produce surprising results.

Modern PHP reduces these risks with type declarations on function parameters, return values, and properties, and optionally with strict types:

<?php
declare(strict_types=1);

function addTax(float $amount): float
{
    return $amount * 1.18;
}

echo addTax(1000);    // 1180
echo addTax("1000");  // TypeError in strict mode

Variables stay dynamic, but function boundaries become type-checked. Type juggling and strict types have their own lessons.

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Inspecting Types

PHP provides several tools to discover a value's type.

Example

<?php
$values = [42, 3.5, "PHP", true, null, [1, 2], new DateTime()];

foreach ($values as $value) {
    printf("%-10s %-10s\n", gettype($value), get_debug_type($value));
}

Output

integer    int       
double     float     
string     string    
boolean    bool      
NULL       null      
array      array     
object     DateTime  

Which Function to Use

Function	Returns	Notes
var_dump($v)	Prints type and value	Best for debugging
gettype($v)	"integer", "double", "boolean", "NULL", …	Older function; uses historical names (double for float)
get_debug_type($v)	"int", "float", "bool", "null", class name	PHP 8.0+. Uses the same names as type declarations and shows the class name for objects. Preferred for error messages.
is_int(), is_string(), is_array(), …	true / false	Best for checking a type in code

Type-Checking Functions

<?php
$input = "42";

var_dump(is_string($input));   // bool(true)
var_dump(is_int($input));      // bool(false)
var_dump(is_numeric($input));  // bool(true)

• is_int("42") is false because the value is a string that contains digits.
• is_numeric("42") is true because it checks whether the value looks like a number (an int, a float, or a numeric string).

This distinction is essential when handling form data and URL parameters, which always arrive as strings.

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Boolean (bool)

A boolean has only two values: true or false. Booleans represent yes/no states and are the result of comparisons.

<?php
$isPublished = true;
$hasStock = 5 > 0;

var_dump($isPublished, $hasStock);

Output

bool(true)
bool(true)

Many values convert to false in conditions (0, "", "0", [], null). These conversion rules are covered in PHP Booleans.

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Integer (int)

An integer is a whole number without a decimal part, positive or negative.

<?php
$quantity = 25;
$temperature = -4;
$hexColor = 0xFF;          // hexadecimal = 255
$permissions = 0o755;      // octal (PHP 8.1+ prefix) = 493
$flags = 0b1010;           // binary = 10
$population = 1_400_000_000; // underscores for readability (PHP 7.4+)

var_dump($hexColor, $permissions, $flags, $population);
echo PHP_INT_MAX;

Output

int(255)
int(493)
int(10)
int(1400000000)
9223372036854775807

• Integers can be written in decimal, hexadecimal (0x), octal (0 or 0o), and binary (0b). They are all stored the same way.
• Underscores in numeric literals are ignored by PHP and make large numbers easier to read.
• On 64-bit systems, integers range from PHP_INT_MIN to PHP_INT_MAX (about ±9.2 quintillion). If a calculation exceeds this, the result becomes a float, losing precision.

Details are covered in PHP Numbers.

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Float (float)

A float (floating-point number, sometimes called a double) is a number with a decimal part or in exponential notation.

<?php
$price = 499.99;
$rate = 1.5e-3;   // 0.0015
$ratio = 10 / 4;

var_dump($price, $rate, $ratio);
var_dump(0.1 + 0.2 == 0.3);

Output

float(499.99)
float(0.0015)
float(2.5)
bool(false)

Why 0.1 + 0.2 == 0.3 Is False

Floats are stored in binary using the IEEE 754 standard. Many decimal fractions, such as 0.1, cannot be represented exactly in binary, just as 1/3 cannot be written exactly in decimal. The tiny rounding errors make 0.1 + 0.2 equal to 0.30000000000000004.

Practical consequence: never compare floats with ==, and avoid floats for money. Store amounts as integers in the smallest unit (paise, cents) or use the BCMath extension. See PHP Floats.

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String (string)

A string is a sequence of characters — technically, a sequence of bytes.

<?php
$name = 'Kavitha';
$greeting = "Hello, $name!";
$tamil = "வணக்கம்";

var_dump($greeting);
var_dump(strlen($tamil), mb_strlen($tamil));

Output

string(15) "Hello, Kavitha!"
int(21)
int(7)

• Single-quoted strings are literal; double-quoted strings interpolate variables and escape sequences.
• strlen() counts bytes. Tamil characters take 3 bytes each in UTF-8, so the 7-character word occupies 21 bytes.
• mb_strlen() counts characters. Always use the mb_* functions for text that may contain non-English characters.

Strings are covered extensively in the string lessons, starting with PHP Strings.

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Array (array)

An array stores multiple values under keys. PHP arrays are ordered maps: they work as lists (numeric keys) and as dictionaries (string keys) at the same time.

<?php
$languages = ["PHP", "Python", "Go"];         // indexed array
$user = ["name" => "Arun", "age" => 28];      // associative array

echo $languages[0] . "\n";
echo $user["name"] . "\n";
var_dump(count($languages));

Output

PHP
Arun
int(3)

Arrays are the most frequently used compound type in PHP: database rows, configuration, JSON data, and form input all appear as arrays. They are covered in the PHP Arrays section.

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Object (object)

An object is an instance of a class. A class defines the structure (properties) and behavior (methods); objects are concrete values created from it.

<?php
class Product
{
    public function __construct(
        public string $name,
        public float $price,
    ) {}

    public function priceWithTax(): float
    {
        return round($this->price * 1.18, 2);
    }
}

$lamp = new Product("Desk Lamp", 999.0);

echo $lamp->name . "\n";
echo $lamp->priceWithTax() . "\n";
var_dump($lamp instanceof Product);

Output

Desk Lamp
1178.82
bool(true)

• new Product(...) creates an object.
• -> accesses properties and methods.
• instanceof checks whether a value is an object of a given class.

Objects let you group data with the code that operates on it. They are covered in the PHP OOP section. PHP also has built-in classes, such as DateTime, PDO, and Exception.

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Callable (callable)

A callable is any value that can be called as a function.

<?php
$double = fn(int $n): int => $n * 2;

$numbers = [1, 2, 3];

print_r(array_map($double, $numbers));
print_r(array_map('strtoupper', ['a', 'b']));
var_dump(is_callable($double));

Output

Array
(
    [0] => 2
    [1] => 4
    [2] => 6
)
Array
(
    [0] => A
    [1] => B
)
bool(true)

Callables let you pass behavior into functions such as array_map(), usort(), and event handlers. See PHP Callback Functions and Anonymous Functions.

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NULL (null)

null represents "no value". A variable is null if it was assigned null, if it was unset, or if it was never assigned (which also raises a warning).

<?php
$middleName = null;

var_dump($middleName);
var_dump(is_null($middleName));
echo $middleName ?? "No middle name";

Output

NULL
bool(true)
No middle name

The ?? (null coalescing) operator returns the right side when the left is null or undefined. See PHP NULL.

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Resource (resource)

A resource is a special handle to something outside PHP — an open file, a network stream, or a process.

<?php
$handle = fopen('php://memory', 'r+');

var_dump($handle);
echo get_debug_type($handle) . "\n";

fclose($handle);

Output

resource(5) of type (stream)
resource (stream)

(The resource number varies.)

• php://memory is a temporary in-memory stream, used here so the example needs no real file.
• Resources should be released when no longer needed (fclose()); PHP also releases them at the end of the request.

Version note: PHP is gradually replacing resources with objects. Since PHP 8.0, for example, curl_init() returns a CurlHandle object and imagecreate() returns a GdImage object instead of resources. File streams from fopen() are still resources.

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How Types Affect Behavior: A Comparison

<?php
$a = "5";
$b = 5;

var_dump($a == $b);   // compares values after conversion
var_dump($a === $b);  // compares values and types
var_dump($a + $b);    // arithmetic converts "5" to a number
var_dump($a . $b);    // concatenation converts 5 to a string

Output

bool(true)
bool(false)
int(10)
string(2) "55"

Explanation

• == (loose equality) converts the values to a common type before comparing, so "5" equals 5.
• === (strict equality) also requires the same type, so a string is never identical to an int.
• + is an arithmetic operator, so PHP converts "5" to the number 5.
• . is the string operator, so PHP converts 5 to "5".

The operator determines the conversion. This automatic conversion is called type juggling and is explained in PHP Type Juggling; explicit conversion is explained in PHP Casting.

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Practical Example: Validating Mixed Input

Data from forms, URLs, JSON, and CSV files must be checked before use, because its type is not guaranteed.

<?php
function describeQuantity(mixed $input): string
{
    if (is_int($input)) {
        return "Integer quantity: $input";
    }

    if (is_string($input) && ctype_digit($input)) {
        return "Numeric string, converted to: " . (int) $input;
    }

    return "Invalid quantity (" . get_debug_type($input) . ")";
}

echo describeQuantity(4) . "\n";
echo describeQuantity("12") . "\n";
echo describeQuantity("12abc") . "\n";
echo describeQuantity(2.5) . "\n";
echo describeQuantity(null) . "\n";

Output

Integer quantity: 4
Numeric string, converted to: 12
Invalid quantity (string)
Invalid quantity (float)
Invalid quantity (null)

How It Works

• mixed declares that the parameter accepts any type, which reflects reality for raw input.
• is_int() accepts real integers.
• ctype_digit() checks that a string contains only digits (0–9), so "12" passes and "12abc" fails. It also rejects negative numbers and decimals, which is appropriate for a quantity.
• (int) $input converts the verified string to an integer.
• get_debug_type() produces a clear type name for the error message.

In production code, filter_var($input, FILTER_VALIDATE_INT) is often used for this purpose; it is covered in PHP Filters.

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Common Mistakes

Assuming Form Data Is Numeric

Problem: $_POST['age'] is always a string, even when the user types 25.

Effect: is_int($_POST['age']) is false, and strict type declarations reject it.

Fix: Validate and convert: filter_var($_POST['age'], FILTER_VALIDATE_INT).

Comparing Floats With ==

Effect: 0.1 + 0.2 == 0.3 is false.

Fix: Compare with a tolerance (abs($a - $b) < 0.00001), or use integers or BCMath for exact decimal values.

Using strlen() for Character Counts

Effect: Wrong lengths for non-English text.

Fix: Use mb_strlen().

Relying on gettype() Names in Comparisons

Effect: gettype(1.5) === 'float' is false, because gettype() returns "double".

Fix: Use is_float() for checks, or get_debug_type() for readable names.

Using == When Types Matter

Effect: Values of different types compare as equal unexpectedly.

Fix: Use === by default.

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Best Practices

• Use var_dump() to inspect values; echo hides type information.
• Use is_*() functions to check types before processing external data.
• Declare parameter, return, and property types in functions and classes.
• Use === and !== for comparisons unless loose comparison is intended.
• Use integers (smallest currency unit) or BCMath for money.
• Use mb_* functions for text.
• Prefer get_debug_type() in error messages (PHP 8.0+).

Official reference: https://www.php.net/manual/en/language.types.php