Hello,
Web Dev.

1 · Variables, Types & Operators

PHP<?php
// Variables start with $ — dynamically typed
$name    = "Alice";          // string (single OR double quotes)
$age     = 30;                // integer
$gpa     = 3.8;               // float
$active  = true;              // boolean (true / false)
$nothing = null;              // null

// Type juggling and checking
gettype($age);                 // "integer"
is_string($name);              // true
(int) "42abc";                 // cast to 42

// Operators
$sum = 5 + 3;                  // + - * / % **  (** = exponent)
$str = "Hello" . " World";    // . = string concatenation
$str .= "!";                   // .= append shorthand

// Comparison
5 ==  "5"   // true  (loose: only value)
5 === "5"   // false (strict: value AND type)
5 !=  6     // true
5 <=> 6     // -1 (spaceship: <0, 0, >0)

// Null coalescing (PHP 7+)
$user = $_GET['user'] ?? "Guest";  // if null, use "Guest"
?>

2 · Output & String Interpolation

PHP<?php
$name = "World";

echo "Hello, $name!";            // variables expand in double quotes
echo "Hello, {$name}s!";          // {} for complex expressions
echo 'Hello, $name';             // single quotes: NO interpolation
print "Hello";                    // like echo, returns 1

// Heredoc (multi-line, interpolates variables)
echo <<<EOT
  <p>Name: $name</p>
  <p>This can span lines.</p>
EOT;

// Common string functions
strlen($name);                   // length: 5
strtoupper($name);               // WORLD
strtolower($name);               // world
str_replace("o", "0", $name);   // W0rld
trim("  hi  ");                  // removes whitespace
explode(",", "a,b,c");           // ["a","b","c"] — split to array
implode("-", ["a","b"]);        // "a-b"   — join array
htmlspecialchars($input);        // ALWAYS escape user input!
?>

3 · Control Flow

PHP<?php
// if / elseif / else
if ($age >= 18) {
    echo "Adult";
} elseif ($age >= 13) {
    echo "Teen";
} else {
    echo "Child";
}

// Ternary shorthand
$label = ($age >= 18) ? "Adult" : "Minor";

// switch
switch ($day) {
    case "Mon": echo "Monday";  break;
    default:   echo "Other day";
}

// match expression (PHP 8 — strict, no fall-through)
$result = match($status) {
    1       => "Active",
    0, -1   => "Inactive",
    default => "Unknown",
};

// Loops
for ($i = 0; $i < 5; $i++) { echo $i; }

while ($x > 0) { $x--; }         // check before each iteration

do { $x--; } while ($x > 0);     // always runs once

foreach ($array as $key => $value) {
    echo "$key: $value";          // iterates arrays/objects
}
?>

4 · Arrays

PHP<?php
// Indexed array
$fruits = ["apple", "banana", "cherry"];
echo $fruits[0];                   // apple (0-indexed)
$fruits[] = "date";               // append

// Associative array (like a dictionary/hash map)
$person = [
    "name"  => "Alice",
    "age"   => 30,
    "email" => "alice@example.com",
];
echo $person["name"];              // Alice

// Multidimensional array
$users = [
    ["name" => "Alice", "age" => 30],
    ["name" => "Bob",   "age" => 25],
];
echo $users[1]["name"];           // Bob

// Array functions
count($fruits);                  // 4
array_push($fruits, "elderberry");
array_pop($fruits);
sort($fruits);                   // alphabetical
in_array("apple", $fruits);     // true
array_map(fn($f) => strtoupper($f), $fruits);  // PHP 7.4 arrow fn
array_filter($fruits, fn($f) => strlen($f) > 5);
?>

5 · Functions

PHP<?php
// Basic function
function greet(string $name, string $greeting = "Hello"): string
{
    return "$greeting, $name!";
}
echo greet("Alice");             // "Hello, Alice!"
echo greet("Bob", "Hi");         // "Hi, Bob!"

// Named arguments (PHP 8)
greet(greeting: "Hey", name: "Carol");

// Variadic (spread) arguments
function sum(int ...$nums): int {
    return array_sum($nums);
}

// Anonymous function (closure)
$double = function(int $n): int { return $n * 2; };

// Arrow function (PHP 7.4+)
$triple = fn(int $n): int => $n * 3;
?>

6 · Superglobals & Form Handling

PHP<?php
// PHP superglobals (always available, any scope)
$_GET     // URL params:  ?name=Alice
$_POST    // Form data:   method="POST"
$_FILES   // Uploaded files
$_SESSION // Persistent across page loads (need session_start())
$_COOKIE  // Browser cookies
$_SERVER  // Server info: IP, request method, URI…
$_ENV     // Environment variables

// Safe form handler pattern
if ($_SERVER['REQUEST_METHOD'] === 'POST') {

    // 1. Retrieve
    $name  = $_POST['name']  ?? '';
    $email = $_POST['email'] ?? '';

    // 2. Sanitize
    $name  = htmlspecialchars(strip_tags(trim($name)));
    $email = filter_var($email, FILTER_SANITIZE_EMAIL);

    // 3. Validate
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        $error = "Invalid email";
    }

    // 4. Use (store, email, redirect…)
    if (empty($error)) {
        header("Location: thankyou.php");   // redirect
        exit;
    }
}
?>

7 · MySQL Database with PDO

PDO (PHP Data Objects) provides a safe, database-agnostic way to run SQL queries. Always use prepared statements to prevent SQL injection.

PHP<?php
// 1. Connect
$dsn = "mysql:host=localhost;dbname=myapp;charset=utf8mb4";
$pdo = new PDO($dsn, 'root', 'password', [
    PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
]);

// 2. CREATE TABLE (run once)
$pdo->exec("
  CREATE TABLE IF NOT EXISTS users (
    id    INT AUTO_INCREMENT PRIMARY KEY,
    name  VARCHAR(100) NOT NULL,
    email VARCHAR(150) NOT NULL UNIQUE
  )
");

// 3. INSERT with prepared statement (:placeholder syntax)
$stmt = $pdo->prepare("INSERT INTO users (name, email) VALUES (:name, :email)");
$stmt->execute([':name' => $name, ':email' => $email]);
$newId = $pdo->lastInsertId();

// 4. SELECT all rows
$rows = $pdo->query("SELECT * FROM users ORDER BY name")->fetchAll();
foreach ($rows as $row) {
    echo "<li>{$row['name']} — {$row['email']}</li>";
}

// 5. SELECT one row
$stmt = $pdo->prepare("SELECT * FROM users WHERE id = :id");
$stmt->execute([':id' => 1]);
$user = $stmt->fetch();
?>

📄 File 2 — config.php (db + helpers)

PHP<?php
// Database credentials (move to .env in production!)
define('DB_HOST', 'localhost');
define('DB_NAME', 'helloworld');
define('DB_USER', 'root');
define('DB_PASS', '');

// PDO connection
try {
    $pdo = new PDO(
        "mysql:host=" . DB_HOST . ";dbname=" . DB_NAME . ";charset=utf8mb4",
        DB_USER, DB_PASS,
        [PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION]
    );

    // Create table if it doesn't exist
    $pdo->exec("
        CREATE TABLE IF NOT EXISTS greetings (
            id         INT AUTO_INCREMENT PRIMARY KEY,
            name       VARCHAR(100) NOT NULL,
            email      VARCHAR(150) NOT NULL,
            created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
        )
    ");

} catch (PDOException $e) {
    die("DB Error: " . $e->getMessage());
}

// Reusable helper function
function sanitize(string $input): string {
    return htmlspecialchars(strip_tags(trim($input)));
}
?>