PHP Course: Beginner to Intermediate

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What it is: This is the starting place for the course. You learn what PHP does and how we will practice.

Why it is used (real-life example): Websites use PHP to show pages that change for each user, like a welcome message after you log in.

Step-by-step

Think of PHP as code that runs on the server (not in the browser).
The server runs PHP and sends back HTML to the browser.
In this course, you will write small PHP files and read their output.

Code example 1: First output

<?php>
echo "Hello from PHP!";
?>

This code uses echo to send text to the browser.

Code example 2: Mixing PHP and HTML

<h1>My Page</h1>
<?php>
echo "<p>This paragraph was created by PHP.</p>";
?>

The browser receives normal HTML, even though PHP built part of it.

Common mistakes

Forgetting the semicolon at the end of a PHP statement.
Writing PHP code outside <?php> tags.
Expecting PHP to run directly in the browser (it must run on a server).

Tips / best practices

Keep one small goal per file while learning.
Read errors carefully; they often point to the exact line.
Use clear text output first, then build HTML later.

Introduction

What it is: PHP is a server-side programming language used to build dynamic web pages.

Why it is used (real-life example): An online store can use PHP to show your cart items and calculate the total price for you.

Step-by-step

A browser sends a request to a server (like asking for index.php).
The server runs the PHP code.
PHP can read data (like URL parameters or form data).
PHP creates a response (often HTML) and sends it back.

Code example 1: Showing the current date

<?php>
echo date("Y-m-d");
?>

date("Y-m-d") creates a text date like 2026-03-23.

Code example 2: Reading a URL value

<?php>
$name = "Guest";
if (isset($_GET["name"])) {
  $name = $_GET["name"];
}
echo "Hello, " . $name;
?>

Step explanation: $_GET holds values from the URL. isset checks if a key exists. Then we print a greeting.

Common mistakes

Using $_GET without checking isset first.
Trusting user input without validation (users can send anything).
Forgetting that PHP runs on the server, so browser console will not show PHP errors.

Tips / best practices

Always treat user input as unsafe until you validate it.
Start by printing simple outputs to understand the request/response flow.
Use meaningful variable names like $name and $total.

Syntax

What it is: Syntax is the set of rules for writing valid PHP code, like where to put semicolons, braces, and variables.

Why it is used (real-life example): When you write correct syntax, your login page or contact form works without breaking.

Step-by-step

PHP code usually starts with <?php.
Statements end with a semicolon ;.
Variables start with $ (example: $age).
Use braces { } for code blocks, like inside if.

Code example 1: Variables and echo

<?php>
$firstName = "Ada";
$age = 20;
echo $firstName;
echo " is " . $age . " years old.";
?>

Step explanation: We store values in variables, then use . to join text together.

Code example 2: If statement

<?php>
$score = 75;
if ($score >= 50) {
  echo "Pass";
} else {
  echo "Fail";
}
?>

The condition $score >= 50 decides which block runs.

Common mistakes

Missing a semicolon after a statement like echo.
Using = (assignment) when you meant == (comparison).
Forgetting to close braces } in an if block.

Tips / best practices

Use consistent indentation so blocks are easy to read.
Prefer strict comparisons when possible, like ===.
Keep lines short and readable while learning.

Variables

What it is: A variable is a named place to store a value, like a number or text.

Why it is used (real-life example): If you store a user name in a variable, you can show it in many places without rewriting the text each time.

Step-by-step

In PHP, a variable starts with $.
Use = to put a value into it.
Use echo to print the variable.

Code example 1

<?php>
$name = "Mina";
echo $name;
?>

This creates a variable named $name and prints its value.

Code example 2

<?php>
$price = 10;
$qty = 3;
$total = $price * $qty;
echo $total;
?>

Here we store numbers and calculate a new value in $total.

Common mistakes

Forgetting the $ at the start of the variable name.
Using spaces in a variable name, like $user name (not allowed).
Using = when you meant comparison (later you will use ==).

Tips / best practices

Use clear names like $firstName or $totalPrice.
Keep variables small and focused: one meaning per variable.
Initialize variables before using them.

Data Types

What it is: A data type is the kind of value you store, like text, number, or true/false.

Why it is used (real-life example): A product price should be a number, but a product name should be text. Using the right type helps avoid wrong results.

Step-by-step

Common types: string (text), int (whole number), float (decimal), bool (true/false), array (list).
PHP can guess the type, but you should understand what you are storing.
Use var_dump() to see the value and its type.

Code example 1

<?php>
$title = "Book";
$pages = 120;
var_dump($title);
var_dump($pages);
?>

var_dump shows that $title is a string and $pages is an integer.

Code example 2

<?php>
$isMember = true;
$rating = 4.5;
var_dump($isMember);
var_dump($rating);
?>

This stores a boolean and a float (decimal number).

Common mistakes

Mixing numbers and text by accident, like "10" + 5 and expecting text output.
Assuming "false" is the same as false (it is not).
Forgetting that decimals like 4.5 are not integers.

Tips / best practices

Use var_dump() while learning to understand what PHP is doing.
Keep data types consistent (prices always numbers, names always strings).
Convert types on purpose when needed (do not rely on guessing).

Operators

What it is: Operators are symbols that do work with values, like adding numbers or joining text.

Why it is used (real-life example): You can calculate a cart total with math operators, and build a greeting message with text operators.

Step-by-step

Math operators: +, -, *, /.
String join operator in PHP is . (dot).
Assignment operator = stores a value in a variable.

Code example 1

<?php>
$subtotal = 50;
$tax = 5;
$total = $subtotal + $tax;
echo $total;
?>

We add two numbers to get a final total.

Code example 2

<?php>
$first = "Hello";
$user = "Sam";
$message = $first . ", " . $user;
echo $message;
?>

We join strings using the dot operator to create one message.

Common mistakes

Using + to join strings (in PHP you should use .).
Forgetting parentheses when needed, which can change the result.
Confusing = (assign) with == (compare).

Tips / best practices

Use parentheses to make math clear, like ($a + $b) * $c.
Build strings in small parts, then join them.
Name variables clearly so your operations read like a story.

Strings

What it is: A string is text, like a name, an email, or a message.

Why it is used: In real life, you show text to users. Example: “Welcome, Sara”.

Step-by-step

Create a string using quotes.
Join (combine) strings using the dot . operator.
Use built-in functions like strlen and strtolower to work with text.

Code example 1: joining text

<?php>
$firstName = "Sara";
$message = "Welcome, " . $firstName . "!";
echo $message; // Welcome, Sara!
?>

Here, . joins pieces of text into one message.

Code example 2: useful string functions

<?php>
$email = "[email protected]";
echo strlen($email); // length of the text
echo "<br>";
echo strtolower($email); // [email protected]
?>

This shows how to get the text length and how to make text lowercase.

Common mistakes

Using + to join strings (PHP uses .).
Forgetting quotes around text.
Mixing single quotes and variables: in single quotes, variables are not replaced.

Tips / best practices

Use double quotes when you want variables inside the text.
Use trim() to remove extra spaces from user input.
Keep user text safe when printing in HTML (escape it later when you learn output safety).

Arrays

What it is: An array is a list that holds many values in one variable.

Why it is used: In real life, you may have a list of product names or a list of user IDs.

Step-by-step

Create an array with [].
Read a value using an index like [0].
Add new values with [] = ....
Loop through values using foreach.

Code example 1: indexed array

<?php>
$colors = ["red", "green", "blue"];
echo $colors[0]; // red
echo "<br>";
$colors[] = "yellow";
echo $colors[3]; // yellow
?>

Index 0 is the first item. Adding with [] puts the item at the end.

Code example 2: looping with foreach

<?php>
$tasks = ["Wash car", "Buy milk", "Study PHP"];
foreach ($tasks as $task) {
  echo "Task: " . $task . "<br>";
}
?>

The loop takes each item and prints it, one by one.

Common mistakes

Using an index that does not exist (it can cause warnings or unexpected results).
Forgetting that arrays start at index 0.
Mixing up arrays and strings (a string is not a list).

Tips / best practices

Use count() to know how many items you have.
Use foreach for simple loops (it is easy to read).
Keep arrays focused: one array for one kind of data (like only names).

Conditionals

What it is: Conditionals let your code make decisions using if, else, and elseif.

Why it is used: In real life, you show different messages. Example: if a user is logged in, show “Dashboard”, else show “Login”.

Step-by-step

Start with an if and a condition that returns true/false.
Run one block when it is true.
Use else for the false case.
Use elseif to check another condition.

Code example 1: simple if/else

<?php>
$isLoggedIn = false;
if ($isLoggedIn) {
  echo "Welcome back!";
} else {
  echo "Please log in.";
}
?>

If $isLoggedIn is true, the first message shows. If not, the second message shows.

Code example 2: elseif for multiple choices

<?php>
$score = 72;
if ($score >= 90) {
  echo "Grade: A";
} elseif ($score >= 70) {
  echo "Grade: B";
} else {
  echo "Grade: C";
}
?>

PHP checks conditions from top to bottom and stops at the first true one.

Common mistakes

Using = instead of == (assignment vs comparison).
Forgetting braces { } and getting confusing results.
Writing conditions that are hard to read (too many checks at once).

Tips / best practices

Keep each condition small and clear.
Use strict comparison === when you want to compare both value and type.
Put the most likely case first to keep logic easy to follow.

Loops

What it is: A loop repeats a block of code. It helps you do the same task many times without writing the same lines again.

Why it is used (real-life example): If you want to show 10 product names, you do not want to write 10 echo lines. A loop can print them one by one.

Step-by-step

Pick a loop type: for is good when you know the count.
Set a start value (example: $i = 1).
Set a condition to keep looping (example: $i <= 5).
Change the value each time (example: $i++).
Put the code to repeat inside the braces { }.

Code example 1: for loop

<?php>
for ($i = 1; $i <= 5; $i++) {
    echo "Item number: " . $i . "<br>";
}
?>

Explanation: $i starts at 1. The loop runs while $i is 5 or less. Each round increases $i by 1.

Code example 2: while loop

<?php>
$count = 3;
while ($count > 0) {
    echo "Countdown: " . $count . "<br>";
    $count--;
}
echo "Done!";
?>

Explanation: The loop checks the condition before each run. When $count becomes 0, it stops.

Common mistakes

Forgetting to change the counter, causing an infinite loop.
Using the wrong condition, like < instead of <=.
Putting ; right after for(...) by mistake, which makes the loop body empty.

Tips / best practices

Keep loop bodies small and easy to read.
Use clear counter names like $i for simple loops, or $index for clarity.
Add a safety limit if the loop depends on user input.

Functions

What it is: A function is a named block of code you can reuse. You can give it input (parameters) and get output (a return value).

Why it is used (real-life example): If you format prices many times (like $9.5 to $9.50), you can write one function and call it everywhere.

Step-by-step

Create a function with function name() { }.
Add parameters inside the parentheses if you need input.
Write the steps inside the braces.
Use return to send a result back.
Call the function by its name.

Code example 1: simple function

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

echo sayHello("Amina");
?>

Explanation: The function takes $name and returns a greeting string. echo prints it.

Code example 2: reusable calculation

<?php>
function addTax($price, $taxRate) {
    $tax = $price * $taxRate;
    $total = $price + $tax;
    return $total;
}

$finalPrice = addTax(100, 0.15);
echo "Final price: " . $finalPrice;
?>

Explanation: $price is the base value. $taxRate is the percent as a decimal (15% is 0.15). The function returns the total.

Common mistakes

Forgetting to return a value when you expect output.
Using a variable inside the function that was never passed in.
Naming functions with unclear names like doStuff().

Tips / best practices

Keep one function doing one job.
Use clear names like formatPrice or calculateTotal.
Add simple input checks when needed (for example, make sure price is not negative).

Scope

What it is: Scope means where a variable can be used. Some variables work only inside a function. Others can be available outside.

Why it is used (real-life example): You may have a global setting like a site name. But inside a function, you might use a temporary variable for a loop. Scope keeps things from mixing by accident.

Step-by-step

A variable created outside a function is in the global scope.
A variable created inside a function is in the local scope (only inside that function).
To use a global variable inside a function, you can use the global keyword.
A better approach is often to pass values into the function as parameters.

Code example 1: local vs global

<?php>
$siteName = "My Shop";

function showSite() {
    $message = "Welcome!";
    echo $message;
}

showSite();
echo "<br>" . $siteName;
?>

Explanation: $message exists only inside showSite(). $siteName is outside and can be used outside.

Code example 2: using global inside a function

<?php>
$counter = 0;

function increaseCounter() {
    global $counter;
    $counter = $counter + 1;
}

increaseCounter();
increaseCounter();
echo "Counter: " . $counter;
?>

Explanation: global $counter; tells PHP to use the global variable, not create a new local one.

Common mistakes

Trying to use a local variable outside the function where it was created.
Forgetting global and thinking the global variable will change.
Overusing global variables, which makes code hard to test and debug.

Tips / best practices

Prefer passing values into functions instead of using global.
Use clear variable names to avoid confusion between global and local values.
Keep variables as local as possible to reduce bugs.

Forms

What it is: A form is HTML inputs (like a text box and a button) that send data to your PHP script.

Why it is used (real-life example): When you log in, sign up, or search on a website, you usually send a form to the server.

Step-by-step

Create an HTML form with a method: GET or POST.
Point the form action to a PHP file.
In PHP, read values from $_GET or $_POST.
Check if a value exists before using it.
Clean the value before showing it on the page.

Code example 1: GET form

<!-- search.html -->
<form action="search.php" method="get">
  <input type="text" name="q" placeholder="Search...">
  <button type="submit">Go</button>
</form>

<?php
// search.php
$q = $_GET['q'] ?? '';
$qSafe = htmlspecialchars($q, ENT_QUOTES, 'UTF-8');
echo 'You searched for: ' . $qSafe;
?>

Explanation: The form sends the input named q in the URL. In PHP, we use $_GET to read it. We also use htmlspecialchars so the user cannot inject HTML.

Code example 2: POST form

<!-- contact.html -->
<form action="contact.php" method="post">
  Name: <input type="text" name="name">
  <button type="submit">Send</button>
</form>

<?php
// contact.php
$name = $_POST['name'] ?? '';
$name = trim($name);
if ($name === '') {
  echo 'Please enter your name.';
} else {
  echo 'Thanks, ' . htmlspecialchars($name, ENT_QUOTES, 'UTF-8') . '!';
}
?>

Explanation: POST sends data in the request body (not in the URL). We use trim to remove extra spaces, then we validate it.

Common mistakes

Using $_GET while the form uses POST (or the opposite).
Assuming a value exists and getting “Undefined index”. Use ?? or isset.
Printing user input without htmlspecialchars (XSS risk).

Tips / best practices

Use POST for sensitive data like passwords.
Always validate and sanitize input before using it.
Show friendly error messages when something is missing.

Sessions

What it is: A session is a way to store small data on the server for one user, across many pages.

Why it is used (real-life example): After a user logs in, you keep them logged in while they visit other pages.

Step-by-step

Start the session with session_start() at the top of the PHP file.
Write values into $_SESSION.
Read values from $_SESSION on the next pages.
To log out, remove session values and destroy the session.

Code example 1: Save a value

<?php
// set_session.php
session_start();
$_SESSION['username'] = 'maria';
echo 'Session saved for username.';
?>

Explanation: session_start() connects PHP to the user’s session. Then we store username on the server.

Code example 2: Read and log out

<?php
// dashboard.php
session_start();
$username = $_SESSION['username'] ?? null;
if ($username === null) {
  echo 'You are not logged in.';
} else {
  echo 'Welcome, ' . htmlspecialchars($username, ENT_QUOTES, 'UTF-8') . '!';
}

// logout.php
session_start();
$_SESSION = [];
session_destroy();
echo 'You are logged out.';
?>

Explanation: We read the value safely using ??. For logout, we clear the session array and call session_destroy().

Common mistakes

Forgetting session_start() (session values will not work).
Calling session_start() after output (can cause header errors).
Storing large data in sessions (it slows things down).

Tips / best practices

Store only small identifiers (like user id), not big arrays.
Regenerate session id after login using session_regenerate_id(true).
Always escape session values when printing them into HTML.

Cookies

What it is: A cookie is a small piece of text stored in the user’s browser. It is sent back to the server on future requests.

Why it is used (real-life example): Remembering a user’s language choice or keeping a “remember me” setting (with care).

Step-by-step

Set a cookie with setcookie() before any output.
Read a cookie from $_COOKIE on later requests.
Delete a cookie by setting it again with an old expiration time.

Code example 1: Set and read a cookie

<?php
// set_cookie.php
$oneWeek = time() + (7 * 24 * 60 * 60);
setcookie('theme', 'dark', $oneWeek, '/');
echo 'Cookie set. Refresh or open read_cookie.php.';
?>

<?php
// read_cookie.php
$theme = $_COOKIE['theme'] ?? 'light';
echo 'Theme is: ' . htmlspecialchars($theme, ENT_QUOTES, 'UTF-8');
?>

Explanation: setcookie tells the browser to store the cookie. On the next request, the browser sends it back and you can read it in $_COOKIE.

Code example 2: Delete a cookie

<?php
// delete_cookie.php
setcookie('theme', '', time() - 3600, '/');
echo 'Cookie deleted.';
?>

Explanation: Setting an expiration time in the past tells the browser to remove the cookie.

Common mistakes

Calling setcookie() after printing output (causes header errors).
Storing secrets in cookies (users can read and change them).
Not using a default value when a cookie does not exist.

Tips / best practices

Only store non-sensitive settings (like theme or language).
When needed, set secure options (like httponly and secure) using the options array in newer PHP versions.
Always escape cookie values before printing.

File Handling

What it is: File handling means reading from a file and writing to a file using PHP. A file can store notes, logs, settings, or exported data.

Why it is used (real-life example): You can save contact form messages into a text file so you can review them later, even without a database.

Step-by-step

Choose a file path (example: data/messages.txt).
Open the file with the correct mode: read (r), write (w), append (a).
Write or read content.
Close the file to free resources.

Code example 1: Append a line to a log file

<?php>
$path = __DIR__ . "/data/visits.log";
$line = date("Y-m-d H:i:s") . " - Visit from " . $_SERVER["REMOTE_ADDR"] . "\n";

$handle = fopen($path, "a");
if ($handle === false) {
    die("Cannot open file");
}

fwrite($handle, $line);
fclose($handle);
echo "Saved";
?>

Explanation: fopen opens the file in append mode, fwrite adds the text, and fclose closes it.

Code example 2: Read a file safely

<?php>
$path = __DIR__ . "/data/visits.log";

if (!file_exists($path)) {
    echo "No log yet.";
    exit;
}

$content = file_get_contents($path);
echo "<pre>" . htmlspecialchars($content) . "</pre>";
?>

Explanation: file_get_contents reads the whole file. htmlspecialchars prevents the browser from running any text as HTML.

Common mistakes

Using w mode by accident (it deletes the old file content).
Not checking if the file exists before reading.
Forgetting to close the file handle.
Showing raw file content without escaping it in HTML pages.

Tips / best practices

Store files outside the public web folder when possible.
Use __DIR__ to build safe paths.
Prefer file_get_contents and file_put_contents for simple tasks.
Always validate and escape user text before saving or displaying.

JSON

What it is: JSON is a simple text format for sharing data. It looks like arrays and objects. PHP can convert arrays to JSON and JSON back to arrays.

Why it is used (real-life example): A JavaScript app may call your PHP page and expect JSON, like a list of products or user settings.

Step-by-step

Create a PHP array with your data.
Convert it to JSON using json_encode.
When receiving JSON, read the text and parse it with json_decode.
Check for errors if the JSON is not valid.

Code example 1: Send JSON output

<?php>
header("Content-Type: application/json; charset=utf-8");

$user = [
    "id" => 7,
    "name" => "Mina",
    "active" => true
];

echo json_encode($user);
?>

Explanation: The header tells the browser it is JSON. json_encode turns the array into JSON text.

Code example 2: Read JSON and convert to array

<?php>
$json = '{"product":"Book","qty":2}';
$data = json_decode($json, true);

if ($data === null && json_last_error() !== JSON_ERROR_NONE) {
    die("Bad JSON: " . json_last_error_msg());
}

echo "Product: " . $data["product"] . ", Qty: " . $data["qty"];
?>

Explanation: json_decode with true returns an associative array. We check errors to avoid using broken data.

Common mistakes

Forgetting true and then trying to use array syntax on an object.
Not checking json_last_error after decoding.
Echoing extra text before JSON (it breaks API responses).
Using single quotes around JSON keys (JSON requires double quotes).

Tips / best practices

Always set Content-Type: application/json when returning JSON.
Use clear data shapes (same keys every time).
Validate incoming data before saving it or using it.
For readable output during learning, try json_encode($data, JSON_PRETTY_PRINT).

Exceptions

What it is: An exception is a special error you can throw and then catch. It helps you stop a bad action and show a friendly message instead of a broken page.

Why it is used (real-life example): If a user uploads a file that is too big, you can throw an exception and tell the user what to fix.

Step-by-step

Put risky code inside try.
If something is wrong, use throw new Exception(...).
Handle it in catch and show a safe message.
Use finally for code that must run (like closing resources).

Code example 1: Basic try/catch

<?php>
function divide($a, $b) {
    if ($b === 0) {
        throw new Exception("You cannot divide by zero");
    }
    return $a / $b;
}

try {
    echo divide(10, 0);
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();
}
?>

Explanation: throw stops the function and sends the problem to catch. The page keeps working and shows a clear message.

Code example 2: finally for cleanup

<?php>
$handle = null;

try {
    $path = __DIR__ . "/data/sample.txt";
    $handle = fopen($path, "r");
    if ($handle === false) {
        throw new Exception("Cannot open the file");
    }
    $text = fread($handle, 50);
    echo htmlspecialchars($text);
} catch (Exception $e) {
    echo "Problem: " . $e->getMessage();
} finally {
    if (is_resource($handle)) {
        fclose($handle);
    }
}
?>

Explanation: finally runs even if an error happens. This is good for closing files and cleaning up.

Common mistakes

Catching exceptions but hiding them without logging anything.
Throwing very generic messages that do not help the user.
Using exceptions for normal flow (like simple if checks).
Showing detailed server errors to users (can expose private info).

Tips / best practices

Use clear messages for users, and log technical details for developers.
Validate input early to prevent exceptions later.
Catch specific exception types when you can (more control).
Keep try blocks small so it is easy to see what may fail.

Classes

What it is: A class is a blueprint for creating objects. It groups data (properties) and actions (methods) in one place.

Why it is used (real-life example): If you build a website with users, you can make a User class to store user data (name, email) and actions (display profile). This keeps your code organized.

Step-by-step

Create a class with class Name.
Add properties to store data.
Add methods to do actions.
Create an object using new.
Use -> to access properties and methods.

Code example 1: Simple class and object

<?php>
class User {
    public $name;

    public function sayHello() {
        return "Hello, I am " . $this->name;
    }
}

$user = new User();
$user->name = "Amina";
echo $user->sayHello();
?>

Explanation: $name is a property. sayHello() is a method. $this means “this object”.

Code example 2: Using a constructor

<?php>
class Product {
    public $title;

    public function __construct($title) {
        $this->title = $title;
    }
}

$p1 = new Product("Notebook");
echo $p1->title;
?>

Explanation: __construct runs automatically when you create the object.

Common mistakes

Forgetting $this-> when using properties inside methods.
Using . instead of -> for object access.
Misspelling method or property names (PHP will not fix spelling for you).

Tips / best practices

Use classes to group related code. It makes code easier to read.
Keep one class focused on one main job (like User or Product).
Start with simple classes before adding more features.

Objects

What it is: An object is a real created thing from a class. It holds its own values and can run its methods.

Why it is used (real-life example): If you have many users, each user is an object. Each object can have different data, like different names and emails.

Step-by-step

Create an object with new ClassName().
Set property values for that object.
Call methods using ->.
Create more objects from the same class when you need more “instances”.

Code example 1: Two objects from one class

<?php>
class Dog {
    public $name;

    public function bark() {
        return $this->name . " says woof";
    }
}

$d1 = new Dog();
$d1->name = "Max";

$d2 = new Dog();
$d2->name = "Luna";

echo $d1->bark();
echo " | ";
echo $d2->bark();
?>

Explanation: $d1 and $d2 are separate objects. Changing one does not change the other.

Code example 2: Copying object references

<?php>
class Counter {
    public $value = 0;
}

$c1 = new Counter();
$c2 = $c1; // both point to the same object

$c2->value = 5;
echo $c1->value; // prints 5
?>

Explanation: In PHP, assigning an object to another variable usually copies the reference. That means both variables can refer to the same object.

Common mistakes

Thinking $c2 = $c1 creates a new separate object (it usually does not).
Trying to access object parts like an array (using []) when it is not an array.
Forgetting to create the object before using it (calling a method on null).

Tips / best practices

Create a new object when you need separate state: use new again.
Use clear variable names like $user or $product to show what the object represents.
When unsure, var_dump($obj) can help you see the object structure while learning.

Inheritance

What it is: Inheritance lets one class (child) reuse and extend another class (parent). The child gets the parent’s properties and methods.

Why it is used (real-life example): You might have a general Account class, and then AdminAccount and CustomerAccount can reuse common code like username handling, but add their own features.

Step-by-step

Create a parent class with shared code.
Create a child class using extends.
Add new methods or properties in the child class.
Optionally override a parent method to change behavior.
Use parent::methodName() if you still want to run the parent method.

Code example 1: Reusing methods with extends

<?php>
class Account {
    public $username;

    public function __construct($username) {
        $this->username = $username;
    }

    public function label() {
        return "User: " . $this->username;
    }
}

class AdminAccount extends Account {
    public function isAdmin() {
        return true;
    }
}

$admin = new AdminAccount("root");
echo $admin->label();
?>

Explanation: AdminAccount automatically gets label() from Account.

Code example 2: Overriding a method

<?php>
class Message {
    public function format($text) {
        return "MSG: " . $text;
    }
}

class HtmlMessage extends Message {
    public function format($text) {
        $base = parent::format($text);
        return "<strong>" . $base . "</strong>";
    }
}

$m = new HtmlMessage();
echo $m->format("Saved");
?>

Explanation: The child method replaces the parent method, but we still call the parent using parent::format().

Common mistakes

Using inheritance when classes are not really related. This makes code confusing.
Forgetting that overridden methods change behavior everywhere you use the child class.
Trying to access private parent properties directly from the child (private means only the parent can use it).

Tips / best practices

Use inheritance only when the child “is a” type of the parent (AdminAccount is an Account).
Keep parent classes small and focused on shared behavior.
When overriding, keep method names and parameter order the same to avoid confusion.

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Graphics Designing/Video Editing

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Home

Step-by-step

Code example 1: First output

Code example 2: Mixing PHP and HTML

Common mistakes

Tips / best practices

Introduction

Step-by-step

Code example 1: Showing the current date

Code example 2: Reading a URL value

Common mistakes

Tips / best practices

Syntax

Step-by-step

Code example 1: Variables and echo

Code example 2: If statement

Common mistakes

Tips / best practices

Variables

Step-by-step

Code example 1

Code example 2

Common mistakes

Tips / best practices

Data Types

Step-by-step

Code example 1

Code example 2

Common mistakes

Tips / best practices

Operators

Step-by-step

Code example 1

Code example 2

Common mistakes

Tips / best practices

Strings

Step-by-step

Code example 1: joining text

Code example 2: useful string functions

Common mistakes

Tips / best practices

Arrays

Step-by-step

Code example 1: indexed array

Code example 2: looping with foreach

Common mistakes

Tips / best practices

Conditionals

Step-by-step

Code example 1: simple if/else

Code example 2: elseif for multiple choices

Common mistakes

Tips / best practices

Loops

Step-by-step

Code example 1: for loop

Code example 2: while loop

Common mistakes

Tips / best practices

Functions

Step-by-step

Code example 1: simple function

Code example 2: reusable calculation

Common mistakes

Tips / best practices

Scope

Step-by-step

Code example 1: local vs global

Code example 2: using global inside a function

Common mistakes

Tips / best practices