PHP Data Types — Complete Guide to PHP Type System

In this tutorial, you will learn about PHP Data Types. We cover key concepts, practical examples, and best practices to help you master this topic.

PHP supports eight data types: four scalar (int, float, string, bool), two compound (array, object), and two special (null, resource) that determine how values are stored and manipulated.

What You'll Learn

By the end of this tutorial, you'll understand all PHP data types, type juggling and casting, strict type declarations, Type Checking functions, and when each type is appropriate.

Why PHP Types Matter

Understanding types prevents bugs from unexpected type conversions, improves code clarity with type declarations, and helps you write more reliable PHP applications for platforms like Laravel.

Real-World Use

A payment processing system uses strict types to ensure amounts are always floats, user IDs are integers, and email addresses are strings, preventing calculation errors.

PHP Data Types Learning Path

flowchart LR
  A[PHP Basics] --> B[Types]
  B --> C[Strings]
  C --> D[Numbers]
  D --> E[Operators]
  A --> F{You Are Here}
  style F fill:#f90,color:#fff

Scalar Types

<?php
$age = 25;             // int
$price = 19.99;        // float
$name = "Alice";       // string
$isActive = true;      // bool
var_dump($age, $price, $name, $isActive);

Compound Types

<?php
$colors = ["red", "green", "blue"];  // array
$user = new stdClass();              // object
$user->name = "Alice";
var_dump($colors, $user);

Type Checking Functions

<?php
$value = "42";
var_dump(is_int($value));    // false
var_dump(is_string($value)); // true
var_dump(is_numeric($value)); // true
var_dump(is_array([1, 2]));  // true
var_dump(is_null(null));     // true

Type Juggling

<?php
var_dump("10" + 5);     // int(15) — string "10" converted to int
var_dump("10" . 5);     // string("105") — int 5 converted to string
var_dump(10 + "5 cars"); // int(15) — PHP 8+ warning, returns 15

Strict Types

<?php
declare(strict_types=1);
function add(int $a, int $b): int {
    return $a + $b;
}
echo add(5, 10);  // 15
// echo add("5", 10);  // TypeError in strict mode

Common Mistakes

1. Assuming Loose Comparison Is Safe

"0" == false is true in loose comparison. Use === for type-safe comparison.

2. Forgetting declare(strict_types=1)

Without strict types, PHP silently converts types. Enable strict types in production code.

3. Confusing is_numeric and is_int

is_numeric("42.5") returns true. is_int("42.5") returns false. Use the appropriate function.

4. Relying on Automatic Type Conversion

"10 apples" + 5 produces 15 with a PHP 8+ deprecation warning. Always validate numeric input.

5. Not Checking Types Before Operations

Passing an array to a string function causes a fatal error. Always verify types before operations.

Practice Questions

1. What are the eight PHP data types?

int, float, string, bool (scalar), array, object (compound), null, resource (special).

2. What is the difference between == and ===?

== compares values after type juggling. === compares both value and type without conversion.

3. What does declare(strict_types=1) do?

It enforces strict type checking for function arguments and return types in the current file, throwing TypeError on mismatch.

4. Why does "10" + 5 return 15?

The + operator triggers numeric context, converting "10" to integer 10. The . operator would concatenate as "105".

5. Challenge: Write a function that safely divides two numbers, handling type mismatches and division by zero.

<?php
declare(strict_types=1);
function safeDivide(int|float $a, int|float $b): int|float|string {
    if ($b === 0) return "Cannot divide by zero";
    return $a / $b;
}
echo safeDivide(10, 3);   // 3.333...
echo safeDivide(10, 0);   // Cannot divide by zero

FAQ

Mini Project: Type Validator

Create a utility function that validates and sanitizes form inputs by type.

<?php
function sanitizeInput(mixed $value, string $type): int|float|string|bool {
    return match($type) {
        "int" => filter_var($value, FILTER_VALIDATE_INT) ?: 0,
        "float" => filter_var($value, FILTER_VALIDATE_FLOAT) ?: 0.0,
        "string" => htmlspecialchars(strip_tags((string)$value)),
        "bool" => filter_var($value, FILTER_VALIDATE_BOOLEAN),
        default => (string)$value
    };
}
echo sanitizeInput("42", "int");      // 42
echo sanitizeInput("<script>alert(1)</script>", "string"); // alert(1)

What's Next

PHP Strings PHP Numbers PHP Arrays