PHP Introduction

beginner

Part of PHP Basics

Theory

PHP (Hypertext Preprocessor) is a widely-used, open-source server-side scripting language designed specifically for web development. It can be embedded directly into HTML and is the backbone of many popular content management systems like WordPress, Drupal, and Joomla.

What is PHP?

PHP code is executed on the server, not in the browser. The server processes PHP code and sends the resulting HTML output to the client. This means users never see your PHP source code — they only see the HTML it generates.

How PHP Works (Request-Response)

Browser (Client)                Server (PHP)
      │                             │
      │──── HTTP Request ────────→  │
      │                             │── PHP Interpreter processes script
      │                             │── Executes code, queries DB, etc.
      │                             │── Generates HTML output
      │←─── HTTP Response (HTML) ───│
      │                             │
      │── Renders HTML in browser

This model allows PHP to:

Generate dynamic content
Read/write files on the server
Process form data
Connect to databases
Manage sessions and cookies

Installing PHP (XAMPP/WAMP/MAMP)

For local development, use an all-in-one package:

XAMPP (cross-platform): Includes PHP, MySQL, Apache, and phpMyAdmin
WAMP (Windows): Apache, MySQL, PHP for Windows
MAMP (macOS): Apache, MySQL, PHP for macOS

After installation, place your PHP files in the web server's document root:

XAMPP: C:/xampp/htdocs/
Linux: /var/www/html/

Start Apache and MySQL from the control panel, then access http://localhost/your-file.php in your browser.

PHP Tags

PHP code is embedded in HTML using opening and closing tags:

<!DOCTYPE html>
<html>
<body>
    <h1>My Page</h1>
    <?php
        echo "Hello from PHP!";
    ?>
</body>
</html>

Short echo tag (works if enabled):

<?= "Hello World" ?>

echo and print

echo and print output text to the browser:

<?php
echo "Hello World";           // Most common
echo "Line 1", " ", "Line 2"; // echo accepts multiple parameters
print "Hello World";          // print returns 1, takes one argument
echo "<h1>HTML tags work too!</h1>";
?>

Comments

<?php
// Single-line comment
 
# Also a single-line comment
 
/*
   Multi-line comment
   spanning multiple lines
*/
 
/**
 * Docblock comment
 * Used before functions and classes
 */
?>

Basic Syntax

PHP scripts start with <?php and end with ?>. Files typically have a .php extension. Every statement ends with a semicolon (;).

<?php
// Variable declaration with $ prefix
$name = "Alice";
$age = 25;
 
// String concatenation with .
echo "Hello, " . $name . "!";
 
// Arithmetic
$sum = 10 + 20;
?>

Variables ($ prefix)

All PHP variables start with the $ symbol. They are dynamically typed — you don't need to declare a type:

<?php
$name = "Alice";     // String
$age = 25;           // Integer
$price = 19.99;      // Float/Double
$isActive = true;    // Boolean
$colors = array("red", "green", "blue"); // Array
$nothing = null;     // Null
?>

Variable names are case-sensitive ($name ≠ $Name).

PHP as a Web Language

PHP excels at web tasks:

Form processing: Handles HTML form submissions
Database access: Connects to MySQL, PostgreSQL, SQLite
Sessions: Maintains user state across pages
File handling: Uploads, reads, and writes files
Email: Sends emails with the mail() function
APIs: Creates and consumes REST APIs
Templating: Generates dynamic HTML pages

Unlike JavaScript (client-side), PHP code runs on the server. You cannot see PHP source code by viewing page source in a browser — you only see the HTML output it produces.

Practical Examples

Example 1: Basic PHP Page with Dynamic Content

php

Example 2: PHP Embedded in HTML

php

Use <?= $variable ?> as a shortcut for <?php echo $variable; ?>. It's cleaner and commonly used in templates. However, never use short tags (<?) without php — they depend on server configuration.

Exercises

Personal Info Page

easy

Create a PHP page that stores your personal information in variables (name, age, city, profession) and displays them in a styled HTML card using echo and string concatenation.

Expected Output:

A styled card showing your name, age, city, and profession

Dynamic Greeting with Time

easy

Create a PHP script that displays a different greeting based on the time of day (morning/afternoon/evening). Also display the current date in a custom format.

Expected Output:

Good morning/afternoon/evening based on the current time, plus the formatted date

Fix the PHP Syntax

medium

Fix the syntax errors in this PHP script. It should display a simple multiplication table.

Expected Output:

5 x 1 = 5\n5 x 2 = 10\n...\n5 x 10 = 50

Mini Quiz

Mini Project

Mini Project: Personal Dashboard

Create a PHP-powered personal dashboard page that displays dynamic content: time-based greeting, current date, a randomly selected quote, server information, and a simple visitor counter stored in a file.

Requirements:

Bonus Challenge

Make the theme change based on the time of day (light theme for daytime, dark theme at night). Add a visit date log.