PHP Programming

PHP (Hypertext Preprocessor) is a widely-used, open-source server-side scripting language designed primarily for web development. This guide covers the core concepts of PHP, from basic syntax to object-oriented programming and database connectivity.

1. Introduction & Environment Setup

PHP code is executed on the server, and the result is returned to the browser as plain HTML.

Setting Up a Local Environment

To run PHP files locally, you need a web server (like Apache or Nginx) and PHP installed. The easiest way to set this up is by using pre-packaged environments:

• XAMPP (Windows, macOS, Linux)
• MAMP (macOS, Windows)
• LocalWP (optimized for WordPress development)
• Docker (for advanced containerized setups)

PHP files use the .php extension. When a user requests a .php file, the server processes the PHP code and sends the generated output to the browser.

2. Basic Syntax & Variables

The PHP Tag

PHP code is written inside <?php and ?> tags. If a file contains only PHP code, it is recommended to omit the closing ?> tag to prevent accidental whitespace issues.

<?php
echo "Hello, World!";

Comments

Comments are ignored by the PHP engine and are used to document code.

<?php
// This is a single-line comment

# This is also a single-line comment

/*
This is a multi-line
comment block
*/

Variables

In PHP, variables start with a dollar sign ($) followed by the variable name.

• Variable names must start with a letter or an underscore.
• They are case-sensitive ($age and $Age are different).
• PHP is a loosely typed language; you do not need to explicitly declare the data type.

<?php
$name = "Alex";
$age = 28;
$height = 1.75;
$is_student = true;

// Outputting variables (using double quotes allows variable interpolation)
echo "My name is $name and I am $age years old.";

3. Data Types

PHP supports several data types:

4. Operators

Arithmetic Operators

Used to perform standard mathematical calculations.

$sum = 10 + 5;        // 15 (Addition)
$difference = 10 - 5; // 5 (Subtraction)
$product = 10 * 5;    // 50 (Multiplication)
$quotient = 10 / 5;   // 2 (Division)
$remainder = 10 % 3;  // 1 (Modulo/Remainder)

Comparison Operators

Used to compare two values. These return a boolean (true or false).

$a = 5;
$b = "5";

$a == $b;   // true  (Equal value)
$a === $b;  // false (Identical: Equal value and same data type)
$a != $b;   // false (Not equal value)
$a !== $b;  // true  (Not identical)
$a > 3;     // true  (Greater than)

5. Control Structures

Conditionals (If-Else)

Conditional statements execute different blocks of code based on conditions.

<?php
$score = 85;

if ($score >= 90) {
    echo "Grade: A";
} elseif ($score >= 80) {
    echo "Grade: B";
} else {
    echo "Grade: C or lower";
}

Switch Statement

Used to compare the same variable against multiple values.

<?php
$fav_color = "blue";

switch ($fav_color) {
    case "red":
        echo "Your favorite color is red.";
        break;
    case "blue":
        echo "Your favorite color is blue.";
        break;
    default:
        echo "Color not recognized.";
}

Loops

Loops run a block of code repeatedly as long as a condition is met.

While Loop

$i = 1;
while ($i <= 5) {
    echo "Number: $i <br>";
    $i++;
}

For Loop

for ($i = 0; $i < 5; $i++) {
    echo "Iteration: $i <br>";
}

6. Functions

Functions are blocks of code that can be repeatedly called.

Declaring and Calling a Function

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

echo greet("Sarah"); // Outputs: Hello, Sarah!

Strict Typing (Optional but Recommended)

You can declare parameter and return types to make code more reliable.

<?php
declare(strict_types=1);

function addNumbers(int $a, int $b): int {
    return $a + $b;
}

echo addNumbers(5, 10); // Outputs: 15

7. Arrays

PHP supports three main types of arrays.

1. Indexed Arrays (Numeric Keys)

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

// Adding an item
$fruits[] = "Orange";

2. Associative Arrays (Named Keys)

<?php
$user = [
    "username" => "johndoe",
    "email" => "[email protected]",
    "age" => 30
];

echo $user["email"]; // Outputs: [email protected]

3. Iterating Over Arrays

The foreach loop is the most efficient way to loop through arrays.

<?php
$prices = ["Laptop" => 800, "Mouse" => 20, "Keyboard" => 50];

foreach ($prices as $item => $price) {
    echo "The $item costs $$price. <br>";
}

8. Working with Forms

PHP uses superglobal variables to collect form data.

• $_GET: Collects data sent via URL parameters (visible to everyone).
• $_POST: Collects data sent via HTTP POST method (hidden from URL, preferred for forms).

HTML Form (form.html)

<form action="process.php" method="POST">
    <label for="username">Username:</label>
    <input type="text" id="username" name="username">
    <input type="submit" value="Submit">
</form>

PHP Handler (process.php)

When processing input, it is vital to sanitize and validate values to prevent security vulnerabilities.

<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Collect and sanitize input
    $username = htmlspecialchars($_POST['username']);
    
    if (!empty($username)) {
        echo "Welcome, " . $username;
    } else {
        echo "Username field is empty.";
    }
}

9. Object-Oriented Programming (OOP) Basics

OOP is a programming model organized around objects rather than actions.

<?php
class Car {
    // Properties (variables inside a class)
    public $brand;
    public $color;

    // Constructor (runs automatically when an object is created)
    public function __construct($brand, $color) {
        $this->brand = $brand;
        $this->color = $color;
    }

    // Method (function inside a class)
    public function getDetails() {
        return "This car is a " . $this->color . " " . $this->brand . ".";
    }
}

// Creating an object (instantiation)
$myCar = new Car("Toyota", "Red");
echo $myCar->getDetails(); // Outputs: This car is a Red Toyota.

10. Database Connection (PDO) & Security

To connect to a database like MySQL, PHP Data Objects (PDO) is recommended because it is secure and supports multiple database drivers.

Connecting to a Database and Running a Safe Query

Always use prepared statements to prevent SQL injection vulnerabilities.

<?php
$host = '127.0.0.1';
$db   = 'my_database';
$user = 'root';
$pass = 'your_password';
$charset = 'utf8mb4';

$dsn = "mysql:host=$host;dbname=$db;charset=$charset";
$options = [
    PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
    PDO::ATTR_EMULATE_PREPARES   => false,
];

try {
    // Create connection
    $pdo = new PDO($dsn, $user, $pass, $options);

    // Prepare a secure SQL query
    $userId = 1;
    $stmt = $pdo->prepare('SELECT username, email FROM users WHERE id = :id');
    
    // Execute with parameters
    $stmt->execute(['id' => $userId]);
    $user = $stmt->fetch();

    if ($user) {
        echo "User: " . htmlspecialchars($user['username']) . " (" . htmlspecialchars($user['email']) . ")";
    } else {
        echo "User not found.";
    }

} catch (PDOException $e) {
    // In production, log errors instead of echoing them directly
    echo "Connection failed: " . $e->getMessage();
}

The guide was created in June 2026.