Unit 11.3B · Term 3

Script Language — PHP

PHP (PHP: Hypertext Preprocessor) is a server-side scripting language designed for web development. Unlike HTML/CSS/JavaScript which run in the browser, PHP runs on the server and generates HTML dynamically. It can process form data, query databases, manage sessions, and produce personalised pages. You'll use XAMPP to run a local Apache server with PHP.

Learning Objectives

  • 11.5.3.8 Use a scripting language to process user input and generate dynamic web content
  • 11.5.3.6 Demonstrate the use of server-side scripts for handling form data

Lesson Presentation

11.3B-php.pdf · Slides for classroom use

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Conceptual Anchor

The Restaurant Kitchen Analogy

HTML is the menu (what the customer sees). The kitchen is the server running PHP. When a customer (browser) places an order (sends a request), the kitchen (PHP) reads the order, prepares the dish (processes data, queries the database), and sends the finished plate (HTML response) to the table. The customer never sees the kitchen — they only receive the result.

Client-Side vs Server-Side

Client-side (HTML, CSS, JS) = runs in the browser. Server-side (PHP) = runs on the server. The browser never sees PHP code — it only receives the HTML output. This is why you need XAMPP: it provides the Apache server that executes PHP.

Setting Up XAMPP

  • Download and install XAMPP from apachefriends.org
  • Start the Apache module from the XAMPP Control Panel
  • Place your PHP files in C:\xampp\htdocs\ (Windows) or /Applications/XAMPP/htdocs/ (Mac)
  • Access your pages at http://localhost/yourfile.php
  • PHP files must have the .php extension, not .html

PHP Fundamentals

Basic Syntax

<?php // PHP code goes between these tags echo "Hello, World!"; // Output text echo "<h1>This is HTML from PHP</h1>"; // Output HTML ?> <!-- PHP embedded in HTML --> <!DOCTYPE html> <html> <body> <h1>Welcome</h1> <p>Today is <?php echo date("l, d F Y"); ?></p> </body> </html>

Variables & Data Types

<?php // Variables start with $ sign — no declaration needed $name = "Alice"; // String $age = 16; // Integer $gpa = 3.85; // Float $isStudent = true; // Boolean // String concatenation uses the dot (.) operator echo "Name: " . $name . ", Age: " . $age; // Variable inside double quotes (interpolation) echo "Hello, $name! You are $age years old."; // Constants — cannot be changed define("SCHOOL", "NIS"); echo SCHOOL; // Output: NIS ?>
PHP Feature Syntax C++ Equivalent
Variable $x = 5; int x = 5;
Output echo "text"; cout << "text";
Concatenation "a" . "b" (dot) "a" + "b" (not directly)
Comparison == != < > <= >= Same
Logical && || ! Same
Array $a = [1, 2, 3]; int a[] = {1, 2, 3};
Typing Dynamic (no type declaration) Static (must declare type)

Control Structures

<?php // IF-ELSE $score = 85; if ($score >= 90) { echo "Grade: A"; } elseif ($score >= 80) { echo "Grade: B"; } else { echo "Grade: C"; } // FOR loop for ($i = 1; $i <= 10; $i++) { echo "$i "; } // WHILE loop $count = 5; while ($count > 0) { echo "Countdown: $count <br>"; $count--; } // FOREACH (great for arrays) $fruits = ["Apple", "Banana", "Cherry"]; foreach ($fruits as $fruit) { echo "$fruit <br>"; } // FOREACH with key $grades = ["Math" => 90, "CS" => 95, "Physics" => 88]; foreach ($grades as $subject => $grade) { echo "$subject: $grade <br>"; } ?>

Functions

<?php // Define a function function greet($name) { return "Hello, $name!"; } echo greet("Alice"); // Output: Hello, Alice! // Function with default parameter function power($base, $exp = 2) { return $base ** $exp; } echo power(3); // Output: 9 (3²) echo power(2, 5); // Output: 32 (2⁵) // Useful built-in functions echo strlen("Hello"); // 5 (string length) echo strtoupper("hello"); // HELLO echo str_replace("a", "o", "cat"); // cot echo count([1, 2, 3, 4]); // 4 (array length) ?>

Worked Example — Form Handling

1 Login Form with PHP Processing

login.html — The form (client-side):

<!DOCTYPE html> <html> <head><title>Login</title></head> <body> <h1>Login</h1> <form action="process_login.php" method="POST"> <label>Username:</label> <input type="text" name="username" required><br> <label>Password:</label> <input type="password" name="password" required><br> <button type="submit">Log In</button> </form> </body> </html>

process_login.php — The processor (server-side):

<?php // Retrieve form data using $_POST $username = $_POST["username"]; $password = $_POST["password"]; // Simple validation (in real apps, check against database) if ($username == "admin" && $password == "secret123") { echo "<h1>Welcome, $username!</h1>"; echo "<p>Login successful.</p>"; } else { echo "<h1>Access Denied</h1>"; echo "<p>Invalid username or password.</p>"; echo '<a href="login.html">Try again</a>'; } ?>
Concept Explanation
action="..." URL of the PHP file that processes the form
method="POST" Send data in HTTP body (hidden). GET sends data in the URL (visible)
name="username" The key used to access this field in PHP
$_POST["username"] PHP superglobal that retrieves POST data by name
$_GET["key"] Same but for GET method data

2 Grade Calculator

calculator.php — Form and Processing in one file:

<!DOCTYPE html> <html> <head><title>Grade Calculator</title></head> <body> <h1>Grade Calculator</h1> <form method="POST" action=""> <label>Student Name:</label> <input type="text" name="name" required><br> <label>Score 1:</label> <input type="number" name="s1" min="0" max="100"><br> <label>Score 2:</label> <input type="number" name="s2" min="0" max="100"><br> <label>Score 3:</label> <input type="number" name="s3" min="0" max="100"><br> <button type="submit" name="calculate">Calculate</button> </form> <?php if (isset($_POST["calculate"])) { $name = $_POST["name"]; $s1 = (int)$_POST["s1"]; $s2 = (int)$_POST["s2"]; $s3 = (int)$_POST["s3"]; $average = ($s1 + $s2 + $s3) / 3; if ($average >= 90) { $grade = "A"; } elseif ($average >= 80) { $grade = "B"; } elseif ($average >= 70) { $grade = "C"; } elseif ($average >= 60) { $grade = "D"; } else { $grade = "F"; } echo "<h2>Results for $name</h2>"; echo "<p>Scores: $s1, $s2, $s3</p>"; echo "<p>Average: " . number_format($average, 1) . "</p>"; echo "<p>Grade: <strong>$grade</strong></p>"; } ?> </body> </html>

GET vs POST

Feature GET POST
Data location URL: page.php?name=Alice&age=16 HTTP body (hidden)
Visible to user? Yes — in address bar No
Data limit ~2048 characters No practical limit
Bookmarkable? Yes No
Security Less secure (data in URL) More secure
Use for Search, filters, non-sensitive data Passwords, forms, data changes
PHP access $_GET["key"] $_POST["key"]

Pitfalls & Common Errors

Opening PHP Files Directly

Double-clicking a .php file opens it as text. PHP must run through a server. Always use http://localhost/file.php via XAMPP, not file://...

Forgetting the $ Sign

All PHP variables start with $. Writing name = "Alice" instead of $name = "Alice" causes a fatal error.

Forgetting Semicolons

Every PHP statement must end with ;. Missing it causes a parse error.

Form name Mismatch

If the HTML input is name="user_name" but PHP reads $_POST["username"], it returns nothing. The name attribute in HTML must exactly match the key in $_POST.

Using == Instead of ===

== does type coercion: "0" == false is TRUE. === checks both value AND type: "0" === false is FALSE. Use === for strict comparison.

Pro-Tips for Exams

Key Exam Points About PHP

  • PHP runs on the server — the browser never sees PHP code
  • PHP can generate dynamic HTML — different output each time
  • Always explain the request-response cycle: browser sends request → server runs PHP → server sends HTML response
  • Know the difference between $_GET and $_POST and when to use each
  • isset() checks if a variable/form field exists before using it

Graded Tasks

Remember

Define: server-side scripting, $_POST, $_GET, echo. Explain what XAMPP provides.

Understand

Draw a diagram showing the request-response cycle between a browser and a PHP server. Label each step.

Apply

Create a registration form (HTML) with name, email, age, and gender fields. Write a PHP script that processes the form and displays a personalised welcome page.

Apply

Write a PHP script with a form where users enter a number. The script outputs the multiplication table (1–12) for that number in an HTML table.

Analyze

A student submits a form using GET with a password field. Explain three problems with this approach and how POST solves them.

Create

Build a mini quiz application: a form with 5 multiple-choice questions. The PHP script checks answers, calculates the score, and displays results with correct answers highlighted.

Self-Check Quiz

1. What symbol must all PHP variables start with?
Click to reveal: The dollar sign ($)
2. What is the PHP string concatenation operator?
Click to reveal: The dot (.) operator. Example: "Hello" . " World"
3. What PHP superglobal retrieves POST form data?
Click to reveal: $_POST["field_name"]
4. Can you open a .php file directly in the browser like an HTML file?
Click to reveal: No — PHP requires a web server (like Apache via XAMPP) to execute.
5. What does isset() check?
Click to reveal: Whether a variable is defined and not null. Used to check if form was submitted.