PHP Cheatsheet

Language Overview

PHP (Hypertext Preprocessor) is a popular server-side scripting language designed primarily for web development. Key characteristics include:

Dynamic, weakly typed language
Embedded in HTML
Runs on the server-side
Widely used for web applications and backend development
Supports object-oriented, procedural, and functional programming paradigms

Basic Syntax

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<?php
// PHP code starts with <?php and ends with ?>
echo "Hello, World!"; // Print statement

// Single-line comment
/* Multi-line
   comment */

// Semicolons are required to end statements
$variable = "Value"; // Variable declaration

Data Types

Primitive Types

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// Integers
$int1 = 42;
$int2 = -17;

// Floating-point numbers
$float = 3.14;

// Strings
$str1 = 'Single quotes';
$str2 = "Double quotes with {$variable} interpolation";

// Booleans
$bool1 = true;
$bool2 = false;

// Null
$null_var = null;

// Special type: Resource (database connections, file handles)
$file_handle = fopen('example.txt', 'r');

Collection Types

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// Indexed Array
$indexed_array = [1, 2, 3, 4, 5];
$indexed_array[] = 6; // Append

// Associative Array (key-value pairs)
$assoc_array = [
    'name' => 'John',
    'age' => 30,
    'city' => 'New York'
];

// Multidimensional Array
$multi_array = [
    'users' => [
        ['name' => 'Alice', 'age' => 25],
        ['name' => 'Bob', 'age' => 30]
    ]
];

Variables and Constants

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// Variable declaration (dynamic typing)
$name = "John";
$age = 30;

// Type casting
$str_to_int = (int)"42";
$int_to_str = (string)42;

// Constants
define('APP_NAME', 'My PHP App');
const MAX_USERS = 100;

// Superglobal variables
echo $_SERVER['REQUEST_METHOD']; // HTTP request method
echo $_GET['param']; // GET parameters
echo $_POST['username']; // POST parameters

Operators

Arithmetic Operators

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$a = 10;
$b = 3;
echo $a + $b;  // Addition
echo $a - $b;  // Subtraction
echo $a * $b;  // Multiplication
echo $a / $b;  // Division
echo $a % $b;  // Modulus
echo $a ** $b; // Exponentiation

Comparison Operators

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$a == $b;   // Equal
$a === $b;  // Identical (type and value)
$a != $b;   // Not equal
$a !== $b;  // Not identical
$a < $b;    // Less than
$a > $b;    // Greater than
$a <= $b;   // Less than or equal
$a >= $b;   // Greater than or equal

Logical Operators

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$x = true;
$y = false;
$x && $y;   // And
$x || $y;   // Or
!$x;        // Not
$x xor $y;  // Exclusive Or

Control Structures

Conditional Statements

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// If-Else
if ($condition) {
    // Code
} elseif ($another_condition) {
    // Code
} else {
    // Code
}

// Ternary Operator
$result = $condition ? $value_if_true : $value_if_false;

// Null Coalescing Operator (PHP 7+)
$username = $_GET['user'] ?? 'Guest';

Loops

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// For Loop
for ($i = 0; $i < 10; $i++) {
    // Code
}

// While Loop
while ($condition) {
    // Code
}

// Do-While Loop
do {
    // Code
} while ($condition);

// Foreach (array iteration)
$array = [1, 2, 3];
foreach ($array as $value) {
    // Code
}

foreach ($assoc_array as $key => $value) {
    // Code
}

// Loop Control
break;    // Exit loop
continue; // Skip current iteration

Functions

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// Basic Function
function greet($name) {
    return "Hello, $name!";
}

// Function with Type Hints (PHP 7+)
function addNumbers(int $a, int $b): int {
    return $a + $b;
}

// Anonymous Functions (Closures)
$multiply = function($a, $b) {
    return $a * $b;
};

// Arrow Functions (PHP 7.4+)
$numbers = [1, 2, 3, 4];
$squared = array_map(fn($n) => $n ** 2, $numbers);

// Variable-length Arguments
function sum(...$numbers) {
    return array_sum($numbers);
}

Object-Oriented Programming

Classes and Objects

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class Person {
    // Properties
    public $name;
    private $age;

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

    // Method
    public function introduce() {
        return "I'm {$this->name}, {$this->age} years old.";
    }
}

// Object Creation
$person = new Person("John", 30);
echo $person->introduce();

// Inheritance
class Student extends Person {
    public $school;

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

// Interfaces
interface Printable {
    public function print();
}

// Traits (Multiple Inheritance Simulation)
trait Loggable {
    public function log($message) {
        echo $message;
    }
}

Error Handling

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// Try-Catch
try {
    // Code that might throw an exception
    if ($error_condition) {
        throw new Exception("An error occurred");
    }
} catch (Exception $e) {
    echo $e->getMessage();
} finally {
    // Optional cleanup code
}

// Custom Error Handling
set_error_handler(function($errno, $errstr) {
    // Custom error logic
});

File I/O

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// Reading Files
$content = file_get_contents('file.txt');
$lines = file('file.txt');

// Writing Files
file_put_contents('output.txt', 'Hello, World!');

// File System Operations
is_file('file.txt');
mkdir('new_directory');
unlink('file.txt'); // Delete file

Database Connectivity (PDO)

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try {
    $pdo = new PDO('mysql:host=localhost;dbname=mydb', 'username', 'password');
    $stmt = $pdo->query('SELECT * FROM users');
    $users = $stmt->fetchAll(PDO::FETCH_ASSOC);
} catch (PDOException $e) {
    echo "Connection failed: " . $e->getMessage();
}

Web Development Features

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// Form Handling
$username = $_POST['username'] ?? '';
$password = $_POST['password'] ?? '';

// Session Management
session_start();
$_SESSION['user_id'] = $user->id;

// Cookies
setcookie('username', 'john_doe', time() + 3600);

// URL Redirection
header('Location: welcome.php');
exit();

Namespaces and Autoloading

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// Namespace Declaration
namespace MyApp\Models;

// Autoloading with Composer
// In composer.json:
// {
//     "autoload": {
//         "psr-4": {
//             "MyApp\\": "src/"
//         }
//     }
// }
// Run: composer dump-autoload

Testing with PHPUnit

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use PHPUnit\Framework\TestCase;

class UserTest extends TestCase {
    public function testUserCreation() {
        $user = new User('john', 'password');
        $this->assertInstanceOf(User::class, $user);
    }
}

Modern PHP Features (PHP 8+)

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// Named Arguments
function createUser(string $name, int $age) { }
createUser(name: 'John', age: 30);

// Attributes
#[Route("/api/posts")]
class PostController { }

// Match Expression
$result = match($status) {
    200 => 'OK',
    404 => 'Not Found',
    default => 'Unknown'
};

// Nullsafe Operator
$country = $user?->getAddress()?->getCountry();

Security Considerations

Always sanitize and validate user inputs
Use prepared statements for database queries
Implement CSRF protection
Use password_hash() for password storage
Enable HTTPS
Keep PHP and dependencies updated

Best Practices

Use Composer for dependency management
Follow PSR coding standards
Use type hints and return type declarations
Leverage modern PHP features
Use framework-agnostic libraries
Implement proper error logging

Resources for Further Learning

Official PHP Documentation: https://www.php.net/docs
PHP-FIG (Framework Interop Group): https://www.php-fig.org/
Composer: https://getcomposer.org/
PHPUnit: https://phpunit.de/
Laravel Framework: https://laravel.com/
Symfony Framework: https://symfony.com/

Performance and Optimization Tips

Use PHP 8+ for best performance
Leverage opcache for bytecode caching
Minimize database queries
Use efficient algorithms
Profile your code with Xdebug
Consider using JIT compilation

Package Management with Composer

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# Install Composer globally
composer global require phpunit/phpunit
# Create new project
composer create-project symfony/skeleton my-project
# Add dependency
composer require symfony/http-client

PHP

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