PHP Programming Guide

Variables and Naming

Variables store data, start with $, and are case-sensitive. Rules: start with a letter or underscore, no numbers at start, use meaningful names.

<?php
// Variable declarations
$name = "John"; // String
$age = 30; // Integer
$price = 19.99; // Float
$isActive = true; // Boolean
$_count = 100; // Valid variable name

// Naming conventions
$userName = "Alice"; // CamelCase
$first_name = "Bob"; // snake_case

// Type casting
$number = (int)"42"; // String to integer
$string = (string)123; // Integer to string

// Variable variables
$varName = "message";
$$varName = "Dynamic variable";
echo $message; // Outputs: Dynamic variable

// Invalid examples: $1name, $#name
echo "Name: " . htmlspecialchars($name) . ", Age: $age";
?>

Data Types

PHP supports 8 primitive types with dynamic typing.

• String: Text data
• Integer: Whole numbers
• Float: Decimal numbers
• Boolean: true/false
• Array: Ordered collections
• Object: Instances of classes
• NULL: No value
• Resource: Special handles (e.g., DB connections)

<?php
$str = "Hello"; // String
$int = 42; // Integer
$float = 3.14; // Float
$bool = true; // Boolean
$arr = [1, 2, 3]; // Array
$null = NULL; // NULL
class User {
    public string $name = "Guest";
}
$obj = new User(); // Object
$resource = fopen("test.txt", "r"); // Resource

// Type checking
var_dump(is_string($str)); // bool(true)
var_dump(gettype($int)); // string "integer"
echo $obj->name; // Guest
?>

Output

Use echo, print, print_r, or var_dump for output.

<?php
// Basic output
echo "Simple output\n";
print "Print works too\n";

// Formatted output
printf("Price: %.2f\n", 19.99);
sprintf("User: %s, Age: %d", "John", 30);

// Debugging output
print_r(["array" => [1, 2, 3]]);
var_dump("Debug info");

// JSON output
echo json_encode(["name" => "Alice", "age" => 25]);
?>

Input

Handle user input securely via forms or CLI.

<?php
// Form input with sanitization
$name = filter_input(INPUT_POST, 'name', FILTER_SANITIZE_STRING) ?? '';
echo "Hello, " . htmlspecialchars($name);

// Command-line input
echo "Enter your name: ";
$name = trim(fgets(STDIN));
echo "Welcome, " . htmlspecialchars($name);

// File input handling
if (isset($_FILES['file'])) {
    $file_name = filter_var($_FILES['file']['name'], FILTER_SANITIZE_STRING);
    echo "Uploaded file: " . htmlspecialchars($file_name);
}
?>

Arithmetic

Perform mathematical operations.

<?php
$a = 10;
$b = 5;
echo $a + $b; // 15
echo $a - $b; // 5
echo $a * $b; // 50
echo $a / $b; // 2
echo $a % $b; // 0
echo $a ** $b; // 100000

// Increment/Decrement
$a++;
echo $a; // 11
$b--;
echo $b; // 4
?>

Comparison

Compare values for equality or order.

<?php
$a = 10;
$b = "10";
var_dump($a == $b); // true
var_dump($a === $b); // false
var_dump($a != $b); // false
var_dump($a !== $b); // true
var_dump($a > $b); // false
var_dump($a <=> $b); // 0

// Null coalescing operator
$name = $_GET['name'] ?? 'Guest';
echo $name;
?>

Logical and Assignment

Combine conditions and assign values.

<?php
$a = true;
$b = false;
var_dump($a && $b); // false
var_dump($a || $b); // true
var_dump(!$a); // false

// Assignment
$x = 10;
$x += 5; // $x = 15
$x ??= 20; // Assign if null
$x *= 2; // $x = 30
echo $x;

// Short-circuit evaluation
$result = $a ?: 'Default';
echo $result;
?>

If-Else

Conditional execution of code.

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

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

// Match expression (PHP 8.0+)
$role = match ($age) {
    18 => "Adult",
    13 => "Teenager",
    default => "Child"
};
echo $role;
?>

Loops

Repeat code execution.

<?php
// For loop
for ($i = 0; $i < 5; $i++) {
    echo "$i ";
}

// While loop
$j = 0;
while ($j < 3) {
    echo "$j ";
    $j++;
}

// Do-while
$k = 0;
do {
    echo "$k ";
    $k++;
} while ($k < 3);

// Foreach with key-value
$colors = ["red" => "#FF0000", "green" => "#00FF00", "blue" => "#0000FF"];
foreach ($colors as $name => $hex) {
    echo "$name: $hex ";
}

// Break and continue
for ($i = 0; $i < 10; $i++) {
    if ($i % 2 === 0) continue;
    if ($i > 5) break;
    echo $i;
}
?>

Switch

Multi-way branching.

<?php
$day = "Monday";
switch ($day) {
    case "Monday":
        echo "Start of week";
        break;
    case "Friday":
        echo "Weekend coming!";
        break;
    default:
        echo "Midweek";
}

// Switch with multiple cases
$code = 404;
switch ($code) {
    case 200, 201:
        echo "Success";
        break;
    case 404:
        echo "Not Found";
        break;
    default:
        echo "Error";
}
?>

Functions

Reusable code blocks with optional parameters.

<?php
// Basic function with type hints
function greet(string $name): string {
    return "Hello, $name!";
}
echo greet("Alice");

// Default parameters
function sayHi(string $name = "Guest"): string {
    return "Hi, $name";
}
echo sayHi();

// Arrow function (PHP 7.4+)
$add = fn(int $a, int $b): int => $a + $b;
echo $add(5, 3);

// Variadic parameters
function sum(...$numbers): int {
    return array_sum($numbers);
}
echo sum(1, 2, 3, 4);

// Anonymous function
$multiply = function(int $a, int $b): int {
    return $a * $b;
};
echo $multiply(4, 5);

// Closure with use
$factor = 2;
$scale = function(int $x) use ($factor): int {
    return $x * $factor;
};
echo $scale(10);
?>

Arrays

Store multiple values in a single variable.

<?php
// Indexed array
$fruits = ["Apple", "Banana", "Cherry"];
echo $fruits[1]; // Banana

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

// Multidimensional array
$matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
];
echo $matrix[1][1]; // 5

// Array functions
$nums = [1, 2, 3];
array_push($nums, 4);
echo count($nums); // 4
$double = array_map(fn($n) => $n * 2, $nums); // [2, 4, 6, 8]
echo implode(", ", $double);

// Array destructuring (PHP 7.1+)
[$a, $b, $c] = $fruits;
echo "$a, $b, $c";

// Array filtering
$evens = array_filter($nums, fn($n) => $n % 2 === 0);
print_r($evens);
?>

Classes and Objects

Define reusable classes with properties and methods.

<?php
class User {
    private string $name;
    private int $age;

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

    public function getName(): string {
        return $this->name;
    }

    public function setAge(int $age): void {
        if ($age < 0) {
            throw new InvalidArgumentException("Age cannot be negative");
        }
        $this->age = $age;
    }
}

$user = new User("Alice", 25);
echo $user->getName(); // Alice
$user->setAge(30);
?>

Inheritance and Interfaces

Extend classes and implement interfaces for polymorphism.

<?php
interface Logger {
    public function log(string $message): void;
}

class User extends Person implements Logger {
    private string $email;

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

    public function log(string $message): void {
        echo "Logging: $message";
    }
}

class Person {
    protected string $name;
    protected int $age;

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

$user = new User("Bob", 30, "bob@example.com");
$user->log("User created");
?>

Form Handling

Securely process form data with validation.

    Name: 
    Email: 
    

                    

PHP Processing (welcome.php):

<?php
if ($_SERVER["REQUEST_METHOD"] === "POST" && isset($_POST['submit'])) {
    $name = filter_input(INPUT_POST, 'name', FILTER_SANITIZE_STRING);
    $email = filter_input(INPUT_POST, 'email', FILTER_SANITIZE_EMAIL);
    if ($name && filter_var($email, FILTER_VALIDATE_EMAIL)) {
        echo "Welcome " . htmlspecialchars($name) . "! Your email is " . htmlspecialchars($email) . ".";
    } else {
        echo "Invalid input. Please provide a valid name and email.";
    }
}
?>

Superglobals

Global variables accessible anywhere.

• $_GET: URL parameters
• $_POST: Form data
• $_SESSION: Session data
• $_COOKIE: Browser cookies
• $_SERVER: Server information
• $_REQUEST: GET, POST, and COOKIE data

<?php
// Secure session handling
session_start([
    'cookie_httponly' => true,
    'use_strict_mode' => true
]);
$_SESSION['username'] = 'admin';

// Secure cookie
setcookie("user", "John", [
    "expires" => time() + 3600,
    "httponly" => true,
    "secure" => true
]);

// Accessing superglobals
echo htmlspecialchars($_SERVER['HTTP_HOST']);
echo isset($_GET['id']) ? htmlspecialchars($_GET['id']) : 'No ID provided';
?>

MySQLi Connection

Connect to MySQL database securely with prepared statements.

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

try {
    $conn = new mysqli($servername, $username, $password, $dbname);
    if ($conn->connect_error) {
        throw new Exception("Connection failed: " . $conn->connect_error);
    }
    
    // Prepared statement
    $stmt = $conn->prepare("SELECT id, name FROM users WHERE id = ?");
    $stmt->bind_param("i", $id);
    $id = 1;
    $stmt->execute();
    $result = $stmt->get_result();
    
    if ($result->num_rows > 0) {
        while ($row = $result->fetch_assoc()) {
            echo "ID: " . $row["id"] . " - Name: " . htmlspecialchars($row["name"]) . "<br>";
        }
    } else {
        echo "No results";
    }
    $stmt->close();
} catch (Exception $e) {
    error_log($e->getMessage());
    echo "An error occurred. Please try again later.";
} finally {
    $conn->close();
}
?>

PDO Connection

Use PDO for database abstraction and security.

<?php
$dsn = "mysql:host=localhost;dbname=myDB;charset=utf8mb4";
$username = "username";
$password = "password";

try {
    $pdo = new PDO($dsn, $username, $password, [
        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
        PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC
    ]);
    
    $stmt = $pdo->prepare("SELECT id, name FROM users WHERE id = :id");
    $stmt->execute(['id' => 1]);
    while ($row = $stmt->fetch()) {
        echo "ID: " . $row["id"] . " - Name: " . htmlspecialchars($row["name"]) . "<br>";
    }
} catch (PDOException $e) {
    error_log($e->getMessage());
    echo "Database error: Please try again later.";
}
?>

Reading Files

Read files safely with error handling.

<?php
try {
    $content = file_get_contents("test.txt");
    if ($content === false) {
        throw new Exception("Cannot read file");
    }
    echo htmlspecialchars($content);
    
    $file = fopen("test.txt", "r");
    if ($file === false) {
        throw new Exception("Cannot open file");
    }
    while (!feof($file)) {
        echo htmlspecialchars(fgets($file)) . "<br>";
    }
    fclose($file);
} catch (Exception $e) {
    echo "Error reading file: " . htmlspecialchars($e->getMessage());
}

// Read CSV file
$csv = array_map('str_getcsv', file('data.csv'));
print_r($csv);
?>

Writing Files

Write to files with error handling.

<?php
try {
    if (file_put_contents("test.txt", "Hello World!") === false) {
        throw new Exception("Cannot write to file");
    }
    
    $file = fopen("test.txt", "a");
    if ($file === false) {
        throw new Exception("Cannot open file");
    }
    fwrite($file, "\nNew line");
    fclose($file);
    
    // Write JSON to file
    $data = ["name" => "John", "age" => 30];
    file_put_contents("data.json", json_encode($data, JSON_PRETTY_PRINT));
} catch (Exception $e) {
    echo "Error writing file: " . htmlspecialchars($e->getMessage());
}
?>