Introducing PHP: A Beginner's Guide

This excerpt from PHP & MySQL: Novice to Ninja, 7th Edition introduces fundamental PHP concepts. We'll cover PHP's server-side nature, basic syntax, variables, operators, comments, and control structures.

PHP: Server-Side Scripting

Unlike client-side languages (HTML, CSS, JavaScript) executed by the browser, PHP runs on the server before sending the page to the browser. This allows for dynamic content generation, enhanced security, and reduced client load. PHP code, enclosed in <?php and ?> tags within .php files, is processed by the server, and the resulting HTML is sent to the browser.

Example: Generating a Random Number

The following code generates a random number:

<code class="language-php"><?php echo rand(1, 10); ?></code>

The browser only sees the generated number, not the PHP code itself. This highlights key advantages: security (server-side generation prevents client-side manipulation), browser compatibility (server-side processing eliminates browser-specific issues), and access to server resources (databases, files, etc.).

Basic Syntax and Statements

PHP syntax resembles C-derived languages. Statements end with semicolons (;). The echo statement outputs content (often HTML):

<code class="language-php">echo 'This is a <strong>test</strong>!';</code>

Strings are enclosed in single (' ') or double (" ") quotes. Functions, identified by parentheses, perform specific tasks (e.g., rand() generates a random number).

Variables, Operators, and Comments

Variables start with a dollar sign ($) (e.g., $testVariable = 3;). PHP is loosely typed; variables can hold various data types. Operators perform mathematical operations ( , -, , /) and string concatenation (.). Comments (// for single-line, / */ for multi-line) explain code.

Control Structures

• if Statements: Execute code blocks conditionally. The == operator checks for equality.

<code class="language-php">if ($roll == 6) {
  echo 'You win!';
}</code>

• else Statements: Provide alternative code execution if the if condition is false.

• Logical Operators: || (or), && (and) combine conditions.

• Loops: Repeat code blocks.

  • for Loops: Iterate a known number of times.

  <code class="language-php"><?php echo rand(1, 10); ?></code>

  • while Loops: Repeat as long as a condition is true.

  <code class="language-php">echo 'This is a <strong>test</strong>!';</code>

  • do...while Loops: Execute code at least once, then repeat based on a condition.

Arrays

Arrays store multiple values. Elements are accessed by index (starting at 0). Associative arrays use string keys.

<code class="language-php">if ($roll == 6) {
  echo 'You win!';
}</code>

User Interaction and Forms

• Passing Variables in Links: Use URL query strings (e.g., name.php?name=Alice). PHP accesses these via $_GET. htmlspecialchars() sanitizes user input to prevent security vulnerabilities (cross-site scripting).

• Passing Variables in Forms: Forms submit data using GET or POST methods. GET appends data to the URL; POST sends data invisibly. $_POST array holds POST data.

Hiding the Seams: PHP Templates and Security

Separate PHP logic from HTML using include statements (include __DIR__ . '/../templates/file.html.php';). This improves maintainability and security. Use absolute paths (with __DIR__) to avoid issues with relative paths and the current working directory.

Many Templates, One Controller

Controllers manage multiple templates based on user interaction. This example uses a form (form.html.php) and a welcome message (welcome.html.php) template.

Frequently Asked Questions (FAQs)

This section provides answers to common beginner questions about PHP syntax, variable usage, arrays, error handling, form handling, file handling, database interaction, session management, and email sending.

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