<?php
echo "Hello, World!";
?>

php hello.php

<?php
// This is a single-line comment
echo "Hello, World!";

/*
This is a multi-line comment
spanning multiple lines
*/
?>

<?php
$name = "John";      // Variable (case-sensitive)
$Name = "Jane";      // Different variable
echo $name;          // Outputs: John
ECHO $Name;          // Outputs: Jane (ECHO works same as echo)
?>

<?php
$name = "Alice";           // String
$age = 25;                 // Integer
$height = 5.8;             // Float
$is_student = true;        // Boolean
$grades = [90, 85, 92];    // Array
$data = null;              // NULL

// Type checking
var_dump($name);           // string(5) "Alice"
echo gettype($age);        // integer
?>

<?php
$single = 'Single quote string';
$double = "Double quote string";
$name = "John";
$greeting = "Hello, $name!";        // Variable interpolation
$greeting2 = 'Hello, $name!';       // No interpolation

echo $greeting;   // Hello, John!
echo $greeting2;  // Hello, $name!

// String concatenation
$full_name = "John" . " " . "Doe";
$full_name .= " Jr.";               // Append

// String functions
echo strlen($name);                 // String length: 4
echo strtoupper($name);            // JOHN
echo strtolower($name);            // john
echo substr($name, 0, 2);          // Jo
?>

<?php
// Indexed array
$fruits = ["apple", "banana", "orange"];
$numbers = array(1, 2, 3, 4, 5);

// Associative array
$person = [
    "name" => "John",
    "age" => 30,
    "city" => "New York"
];

// Multidimensional array
$students = [
    ["name" => "Alice", "grade" => 90],
    ["name" => "Bob", "grade" => 85],
    ["name" => "Carol", "grade" => 92]
];

// Accessing arrays
echo $fruits[0];                    // apple
echo $person["name"];               // John
echo $students[0]["grade"];         // 90

// Array functions
echo count($fruits);                // 3
array_push($fruits, "grape");       // Add element
print_r($fruits);                   // Display array
?>

<?php
$a = 10;
$b = 3;

echo $a + $b;    // Addition: 13
echo $a - $b;    // Subtraction: 7
echo $a * $b;    // Multiplication: 30
echo $a / $b;    // Division: 3.333...
echo $a % $b;    // Modulus: 1
echo $a ** $b;   // Exponentiation: 1000
?>

<?php
$x = 5;
$y = "5";

var_dump($x == $y);   // true (equal value)
var_dump($x === $y);  // false (identical type and value)
var_dump($x != $y);   // false
var_dump($x !== $y);  // true
var_dump($x > 3);     // true
var_dump($x <= 5);    // true
?>

<?php
$a = true;
$b = false;

var_dump($a && $b);   // false (AND)
var_dump($a || $b);   // true (OR)
var_dump(!$a);        // false (NOT)
var_dump($a and $b);  // false (AND, lower precedence)
var_dump($a or $b);   // true (OR, lower precedence)
?>

<?php
$age = 20;

if ($age >= 18) {
    echo "Adult";
} elseif ($age >= 13) {
    echo "Teen";
} else {
    echo "Child";
}

// Ternary operator
$status = ($age >= 18) ? "Adult" : "Minor";
echo $status;

// Null coalescing operator (PHP 7+)
$username = $_GET['user'] ?? 'guest';
?>

<?php
$day = "Monday";

switch ($day) {
    case "Monday":
    case "Tuesday":
    case "Wednesday":
    case "Thursday":
    case "Friday":
        echo "Weekday";
        break;
    case "Saturday":
    case "Sunday":
        echo "Weekend";
        break;
    default:
        echo "Invalid day";
}
?>

<?php
for ($i = 0; $i < 5; $i++) {
    echo "Number: $i\n";
}

// foreach for arrays
$fruits = ["apple", "banana", "orange"];
foreach ($fruits as $fruit) {
    echo $fruit . "\n";
}

// foreach with key-value pairs
$person = ["name" => "John", "age" => 30];
foreach ($person as $key => $value) {
    echo "$key: $value\n";
}
?>

<?php
$count = 0;
while ($count < 3) {
    echo "Count: $count\n";
    $count++;
}

$num = 0;
do {
    echo "Number: $num\n";
    $num++;
} while ($num < 3);
?>

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

echo greet("Alice");

// Function with default parameters
function calculate_area($length, $width = 1) {
    return $length * $width;
}

echo calculate_area(5);      // 5 (width defaults to 1)
echo calculate_area(5, 3);   // 15

// Variable arguments
function sum(...$numbers) {
    return array_sum($numbers);
}

echo sum(1, 2, 3, 4);        // 10

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

echo $multiply(4, 5);        // 20
?>

<?php
$global_var = "I'm global";

function test_scope() {
    global $global_var;
    $local_var = "I'm local";

    echo $global_var;        // Accessible with 'global' keyword
    echo $local_var;         // Local to this function
}

test_scope();

// Static variables
function counter() {
    static $count = 0;
    $count++;
    echo "Count: $count\n";
}

counter();  // Count: 1
counter();  // Count: 2
counter();  // Count: 3
?>

<?php
class Person {
    // Properties
    private $name;
    private $age;
    public $city;

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

    // Methods
    public function getName() {
        return $this->name;
    }

    public function setAge($age) {
        if ($age > 0) {
            $this->age = $age;
        }
    }

    public function getAge() {
        return $this->age;
    }

    public function introduce() {
        return "Hi, I'm {$this->name}, {$this->age} years old from {$this->city}";
    }
}

// Creating objects
$person1 = new Person("John", 25, "New York");
$person2 = new Person("Jane", 30);

echo $person1->introduce();
echo $person2->getName();
?>

<?php
class Animal {
    protected $name;
    protected $species;

    public function __construct($name, $species) {
        $this->name = $name;
        $this->species = $species;
    }

    public function makeSound() {
        return "{$this->name} makes a sound";
    }

    public function getInfo() {
        return "{$this->name} is a {$this->species}";
    }
}

class Dog extends Animal {
    private $breed;

    public function __construct($name, $breed) {
        parent::__construct($name, "Dog");
        $this->breed = $breed;
    }

    public function makeSound() {
        return "{$this->name} barks";
    }

    public function fetch() {
        return "{$this->name} fetches the ball";
    }
}

$dog = new Dog("Buddy", "Golden Retriever");
echo $dog->getInfo();      // Buddy is a Dog
echo $dog->makeSound();    // Buddy barks
echo $dog->fetch();        // Buddy fetches the ball
?>

<?php
// Try-catch for exceptions
try {
    $result = 10 / 0;
    throw new Exception("Custom error message");
} catch (DivisionByZeroError $e) {
    echo "Division by zero error: " . $e->getMessage();
} catch (Exception $e) {
    echo "General error: " . $e->getMessage();
} finally {
    echo "This always executes";
}

// Custom exception class
class CustomException extends Exception {
    public function errorMessage() {
        return "Custom error on line {$this->getLine()} in {$this->getFile()}: {$this->getMessage()}";
    }
}

try {
    throw new CustomException("Something went wrong!");
} catch (CustomException $e) {
    echo $e->errorMessage();
}
?>

<?php
// Reading files
$content = file_get_contents("example.txt");
echo $content;

// Writing files
file_put_contents("output.txt", "Hello, PHP!");

// File operations with error handling
if (file_exists("data.txt")) {
    $lines = file("data.txt", FILE_IGNORE_NEW_LINES);
    foreach ($lines as $line) {
        echo $line . "\n";
    }
} else {
    echo "File not found";
}

// Working with file handles
$handle = fopen("log.txt", "a");
if ($handle) {
    fwrite($handle, "Log entry: " . date("Y-m-d H:i:s") . "\n");
    fclose($handle);
}
?>

<?php
// HTML form (save as form.html)
/*
<form method="POST" action="process.php">
    <input type="text" name="username" placeholder="Username">
    <input type="email" name="email" placeholder="Email">
    <input type="password" name="password" placeholder="Password">
    <button type="submit">Submit</button>
</form>
*/

// Processing form data (process.php)
if ($_POST) {
    $username = $_POST['username'] ?? '';
    $email = $_POST['email'] ?? '';
    $password = $_POST['password'] ?? '';

    // Validation
    if (empty($username) || empty($email) || empty($password)) {
        echo "All fields are required";
    } elseif (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        echo "Invalid email format";
    } else {
        // Process the data
        echo "Welcome, " . htmlspecialchars($username);
        // Hash password
        $hashed_password = password_hash($password, PASSWORD_DEFAULT);
        // Save to database, etc.
    }
}

// Working with GET parameters
$page = $_GET['page'] ?? 1;
$category = $_GET['category'] ?? 'all';
echo "Page: $page, Category: $category";
?>

<?php
// Database connection using PDO
try {
    $pdo = new PDO(
        "mysql:host=localhost;dbname=mydb;charset=utf8",
        "username",
        "password",
        [PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION]
    );

    // Prepared statements (secure)
    $stmt = $pdo->prepare("SELECT * FROM users WHERE age > ? AND city = ?");
    $stmt->execute([18, "New York"]);

    while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
        echo "User: " . $row['name'] . "\n";
    }

    // Insert data
    $stmt = $pdo->prepare("INSERT INTO users (name, email, age) VALUES (?, ?, ?)");
    $stmt->execute(["John Doe", "[email protected]", 25]);

    echo "Last inserted ID: " . $pdo->lastInsertId();

} catch (PDOException $e) {
    echo "Database error: " . $e->getMessage();
}
?>

<?php
// Named arguments (PHP 8.0+)
function createUser($name, $email, $age = 18, $active = true) {
    return compact('name', 'email', 'age', 'active');
}

$user = createUser(
    name: "John",
    email: "[email protected]",
    active: false
);

// Match expression (PHP 8.0+)
$status_code = 200;
$message = match($status_code) {
    200, 201 => 'Success',
    400 => 'Bad Request',
    404 => 'Not Found',
    500 => 'Server Error',
    default => 'Unknown Status'
};

// Nullsafe operator (PHP 8.0+)
$user_name = $user?->profile?->name ?? 'Unknown';

// Constructor property promotion (PHP 8.0+)
class User {
    public function __construct(
        public string $name,
        public string $email,
        public int $age = 18,
        private bool $active = true
    ) {}

    public function isActive(): bool {
        return $this->active;
    }
}

$user = new User("John", "[email protected]", 25);
echo $user->name;  // John

// Enums (PHP 8.1+)
enum Status {
    case PENDING;
    case APPROVED;
    case REJECTED;

    public function label(): string {
        return match($this) {
            Status::PENDING => 'Pending',
            Status::APPROVED => 'Approved',
            Status::REJECTED => 'Rejected',
        };
    }
}

$status = Status::PENDING;
echo $status->label();  // Pending
?>

<?php
// 1. Always use PHP opening tags
// Good: <?php
// Avoid: <? (short tags)

// 2. Use prepared statements for database queries
// Prevents SQL injection
$stmt = $pdo->prepare("SELECT * FROM users WHERE id = ?");
$stmt->execute([$user_id]);

// 3. Validate and sanitize input
$email = filter_var($_POST['email'], FILTER_VALIDATE_EMAIL);
$name = htmlspecialchars($_POST['name'], ENT_QUOTES, 'UTF-8');

// 4. Use meaningful variable names
// Good:
$user_age = 25;
$is_active = true;

// Bad:
$a = 25;
$flag = true;

// 5. Handle errors gracefully
function divide($a, $b) {
    if ($b == 0) {
        throw new InvalidArgumentException("Division by zero");
    }
    return $a / $b;
}

// 6. Use type declarations (PHP 7+)
function calculateTotal(array $items): float {
    return array_sum($items);
}

// 7. Organize code with namespaces
namespace App\Models;

class User {
    // class implementation
}

// 8. Use composer for dependency management
// composer.json example:
/*
{
    "require": {
        "monolog/monolog": "^2.0"
    },
    "autoload": {
        "psr-4": {
            "App\\": "src/"
        }
    }
}
*/
?>