Session 3.1 – Introduction to PHP

Module 3: PHP Basics | Duration: 1 hr

Learning Objectives

By the end of this session, students will be able to:

Understand what PHP is and its role in web development
Identify the key features and capabilities of PHP
Write and execute basic PHP programs
Understand PHP syntax and code structure
Embed PHP code within HTML documents
Use different types of comments in PHP

Introduction to Server-Side Scripting

Before diving into PHP, it's essential to understand the concept of server-side scripting. Unlike client-side languages like JavaScript that run in the browser, server-side scripts execute on the web server and send the results to the client.

Client-Side Scripting

Executes in the browser
Visible to users (view source)
Limited access to server resources
Examples: JavaScript, HTML, CSS

Server-Side Scripting

Executes on the web server
Code hidden from users
Full access to server resources
Examples: PHP, Python, Node.js, Ruby

What is PHP?

Definition

PHP (Hypertext Preprocessor) is a widely-used open-source server-side scripting language especially suited for web development and can be embedded into HTML.

Key Facts About PHP

Created in 1994

Originally created by Rasmus Lerdorf as "Personal Home Page Tools"

78% of Websites

Powers approximately 78% of all websites with a known server-side language

Open Source

Free to download and use under the PHP License

Popular Platforms Built with PHP

WordPress, Facebook, Wikipedia, Slack, Etsy, MailChimp, and many more major platforms rely on PHP.

PHP Features and Capabilities

Simple & Fast

Easy to learn with a straightforward syntax similar to C and Java

Embedded in HTML

Can be seamlessly integrated within HTML code

Database Support

Supports MySQL, PostgreSQL, MongoDB, Oracle, and more

Cross-Platform

Runs on Windows, Linux, macOS, and Unix systems

Secure

Built-in security features for web applications

OOP Support

Object-oriented programming capabilities

What Can PHP Do?

Generate dynamic page content
Create, open, read, write, delete, and close files on the server
Collect form data
Send and receive cookies
Add, delete, modify data in your database
Control user access
Encrypt data
Output images, PDF files, and even Flash movies

Basic PHP Syntax

PHP Tags

PHP code is enclosed within special tags that tell the server where PHP code begins and ends:

<?phplt;?phplt;?php
    // Your PHP code goes here
?>

Important Notes

PHP files must have a .php extension
PHP code can be placed anywhere in the document
The closing tag ?> can be omitted if the file contains only PHP code (recommended)
PHP statements end with a semicolon (;)

PHP Statements

Every PHP statement must end with a semicolon:

<?phplt;?phplt;?php
    echo "Hello, World!";
    echo "Welcome to PHP";
?>

Case Sensitivity

In PHP:

Keywords (if, else, while, echo, etc.) are NOT case-sensitive
Variables ARE case-sensitive

<?phplt;?phplt;?php
    // These are all valid and equivalent
    ECHO "Hello";
    echo "Hello";
    EcHo "Hello";

    // But variables ARE case-sensitive
    $name = "John";
    $NAME = "Jane";
    // $name and $NAME are different variables!
?>

Your First PHP Program

Example 1: Simple Output

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

Output:
Hello, World!

Example 2: Using Variables

<?phplt;?phplt;?php
    $greeting = "Hello";
    $name = "Alice";

    echo $greeting . ", " . $name . "!";
?>

Output:
Hello, Alice!

Example 3: Multiple Echo Statements

<?phplt;?phplt;?php
    echo "<h1>Welcome to PHP</h1>";
    echo "<p>PHP is a powerful server-side language.</p>";
    echo "<p>It can generate dynamic web content.</p>";
?>

Output:

Welcome to PHP

PHP is a powerful server-side language.

It can generate dynamic web content.

Comments in PHP

Comments are used to document code and are ignored by the PHP engine. They help make code more readable and maintainable.

Types of Comments

1. Single-Line Comments

<?phplt;?phplt;?php
    // This is a single-line comment
    echo "Hello"; // Comment after code

    # This is also a single-line comment (Unix shell style)
    echo "World";
?>

2. Multi-Line Comments

<?phplt;?phplt;?php
    /*
     * This is a multi-line comment
     * It can span multiple lines
     * Useful for detailed explanations
     */
    echo "Hello, World!";
?>

Best Practices for Comments

Use comments to explain WHY, not WHAT
Keep comments up-to-date with code changes
Don't over-comment obvious code
Use multi-line comments for function/class documentation

Embedding PHP in HTML

One of PHP's greatest strengths is its ability to be embedded directly within HTML code. This allows for dynamic content generation.

Example: Mixed HTML and PHP

<!DOCTYPE html>
<html>
<head>
    <title>PHP Example</title>
</head>
<body>
    <h1>Welcome to My Website</h1>

    <?php
        $currentTime = date("h:i A");
        $currentDate = date("F j, Y");

        echo "<p>Current time: " . $currentTime . "</p>";
        echo "<p>Today's date: " . $currentDate . "</p>";
    ?>

    <p>This is regular HTML content.</p>
</body>
</html>

Multiple PHP Blocks

You can have multiple PHP code blocks in a single file:

<!DOCTYPE html>
<html>
<body>
    <?php $title = "My Page"; ?>

    <h1><?php echo $title; ?></h1>

    <p>Content goes here</p>

    <?php
        for ($i = 1; $i <= 5; $i++) {
            echo "<p>Line " . $i . "</p>";
        }
    ?>
</body>
</html>

Short Echo Tag

PHP 5.4+ supports a short echo tag: <?= $variable ?> which is equivalent to <?phplt;?phplt;?php echo $variable; ?>

Session Summary

Key Points

PHP is a server-side scripting language designed for web development
PHP code executes on the server and sends HTML to the client
PHP is open-source, cross-platform, and powers millions of websites
PHP code is enclosed in <?phplt;?phplt;?php ... ?> tags
All PHP statements must end with a semicolon (;)
PHP keywords are case-insensitive, but variables are case-sensitive
Comments can be single-line (//) or multi-line (/* */)
PHP can be seamlessly embedded within HTML code
The echo statement is used to output text and HTML

Next Session Preview

In the next session, we will explore PHP Variables and Data Types, learning how to store and manipulate different types of data in PHP.

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