Knowledge Base

What is PHP?

PHP stands for "PHP: Hypertext Preprocessor" (originally "Personal Home Page"). It is a server-side scripting language designed specifically for web development. That is, it allows websites to generate dynamic content. Used in conjunction with HTML, it controls the behavior of web pages, interacts with databases, and responds to user interactions. One of the biggest advantages of PHP is that it is relatively easy to learn and has a large developer community. This means access to a large number of resources, libraries, and frameworks. If you are looking for information about Web Software Services, it is important to evaluate the opportunities offered by different platforms and technologies.

Key Points:

• It is a server-side language.
• It is optimized for web development.
• It works integrated with HTML.
• It provides database interaction.
• It is easy to learn.
• It has a large community.

What Does PHP Do? In Which Areas Is It Used?

PHP has a wide range of uses. Its main uses are:

• Dynamic Websites: User-interactive, constantly updated websites (e.g., social media platforms, e-commerce sites, blogs).
• Web Applications: Web applications that perform complex operations such as data processing, user management, and security.
• Content Management Systems (CMS): Most popular CMSs such as WordPress, Joomla, and Drupal are developed with PHP. These systems allow users to easily manage their websites.
• E-commerce Platforms: E-commerce platforms such as WooCommerce and Magento are preferred thanks to the security and scalability provided by PHP.
• Database Applications: Data storage, querying, and updating operations by interacting with databases such as MySQL and PostgreSQL.
• Graphic Processing: Simple graphic creation and editing with the GD library.
• Session Management: Tracking and managing user sessions.

Real-Life Examples:

• Facebook: Initially developed largely with PHP.
• Wikipedia: MediaWiki software is written in PHP.
• WordPress: The world's most popular CMS.

How Does PHP Work?

The working principle of PHP is as follows:

1. User Sends Request: The user sends a request through a web browser to access a web page.
2. Web Server Receives Request: The web server (e.g., Apache or Nginx) receives this request.
3. PHP Engine Engages: The server sends PHP files to the PHP engine.
4. PHP Code is Processed: The PHP engine interprets and executes the PHP code.
5. HTML Output is Generated: After the PHP code is executed, HTML output is generated. This output includes dynamic content.
6. Web Server Sends Response: The web server sends the generated HTML output back to the user.
7. Browser Displays: The user's web browser interprets the HTML output and displays the web page.

Schematic Representation (Textual):

User (Browser) --> Web Server (Apache/Nginx) --> PHP Engine --> Database (MySQL) --> PHP Engine --> Web Server --> User (Browser)

How to Set Up a Web Development Environment with PHP?

To do web development with PHP, you need to set up a development environment. This environment includes the PHP engine, a web server, and a database. There are several different methods for installation:

1. Manual Installation: Involves installing and configuring PHP, a web server (Apache/Nginx), and a database (MySQL/MariaDB) separately. This method provides more control but is more complex.
2. XAMPP/WAMP/MAMP: These packages offer PHP, Apache, MySQL, and other necessary tools in a single package. Installation and configuration are much easier.
3. Docker: Using Docker, you can create containers that include PHP, a web server, and a database. This method provides a consistent development environment across different environments.
4. Online IDEs: Online IDEs like CodePen and Repl.it allow you to run PHP code directly in the browser. No installation is required, but there may be some limitations.

Installation with XAMPP (Step by Step):

1. Download XAMPP from the official website.
2. Run the downloaded file to install XAMPP.
3. Make sure to select Apache and MySQL during installation.
4. After the installation is complete, open the XAMPP Control Panel.
5. Start the Apache and MySQL services.
6. Visit "localhost" or "127.0.0.1" in your web browser. You should see the XAMPP welcome page.
7. Save your PHP files in the "htdocs" folder (located in the XAMPP installation directory).
8. You can access your PHP files from the browser as "localhost/file_name.php".

Code Example (with XAMPP):

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

Save this code as "merhaba.php" in the "htdocs" folder and visit "localhost/merhaba.php" in your browser. You should see "Hello World!" on the screen.

What is the Basic Syntax of PHP?

The basic syntax of PHP is as follows:

• Tags: PHP code is written between the <?php and ?> tags.
• Variables: Variables start with the $ sign. For example: $name = "Ahmet";
• Data Types: The main data types in PHP are:
  • String (Text)
  • Integer (Whole Number)
  • Float (Decimal Number)
  • Boolean (True/False)
  • Array (Array)
  • Object (Object)
  • NULL (Empty)
• Operators: Arithmetic operators (+, -, *, /), comparison operators (==, !=, >, <, >=, <=), logical operators (&&, ||, !) are used.
• Control Structures: Conditional statements such as if, else, elseif, switch and loops such as for, while, do-while are used.
• Functions: Functions are defined to prevent code repetition and provide modularity.
• Comments: Comments are used to increase code readability. // is used for single-line comments, and /* ... */ is used for multi-line comments.

Code Examples:

<?php
  // Variable definition
  $name = "Ayşe";
  $age = 30;

  // Conditional statement
  if ($age >= 18) {
    echo "$name is an adult.";
  } else {
    echo "$name is not an adult.";
  }

  // Loop
  for ($i = 0; $i < 5; $i++) {
    echo "Number: " . $i . "<br>";
  }

  // Function definition
  function add($number1, $number2) {
    return $number1 + $number2;
  }

  // Function call
  $result = add(5, 3);
  echo "Total: " . $result;
?>

What are PHP Frameworks and Why are They Used?

PHP frameworks are pre-written code libraries used to develop web applications faster, more securely, and in a more organized manner. Frameworks simplify repetitive tasks, provide code standardization, and reduce security vulnerabilities.

Popular PHP Frameworks:

• Laravel: One of the most popular PHP frameworks. Known for its elegant syntax, powerful tools, and large community. Uses the MVC (Model-View-Controller) architecture.
• Symfony: A flexible and scalable framework. Suitable for large projects and complex applications. Used as a base by many PHP projects.
• CodeIgniter: An easy-to-learn and lightweight framework. Ideal for rapid prototyping and small projects.
• CakePHP: A framework designed for rapid development. Adopts the convention over configuration principle.
• Zend Framework: A modular framework designed for enterprise-level applications.

Advantages of Using a Framework:

• Rapid Development: Frameworks shorten development time by simplifying repetitive tasks.
• Code Standardization: Frameworks ensure that the code conforms to a specific standard, making it easier to read and maintain.
• Security: Frameworks provide protection against common security vulnerabilities.
• MVC Architecture: Frameworks often use the MVC architecture, which makes the code more organized and manageable.
• Community Support: Popular frameworks have a large community, which helps in solving problems.

MVC Architecture (Textual Description):

• Model: Interacts with the database, manages data.
• View: Creates the user interface, displays data.
• Controller: Receives user requests, manages the model and view.

How to Perform Database Operations with PHP?

PHP can interact with many database systems such as MySQL, PostgreSQL, and SQLite. PDO (PHP Data Objects) or MySQLi (MySQL Improved) extensions are generally used for database operations.

Database Connection with PDO (MySQL):

<?php
  $servername = "localhost";
  $username = "username";
  $password = "password";
  $dbname = "databasename";

  try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    // Set the error mode to exception
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    echo "Successfully connected to the database";
  } catch(PDOException $e) {
    echo "Connection error: " . $e->getMessage();
  }
?>

Adding Data (PDO):

<?php
  // ... (Database connection) ...

  try {
    $sql = "INSERT INTO kullanicilar (isim, email) VALUES ('Ali', '[email protected]')";
    // Execute the SQL query
    $conn->exec($sql);
    echo "New record added successfully";
  } catch(PDOException $e) {
    echo $sql . "<br>" . $e->getMessage();
  }

  $conn = null; // Close the connection
?>

Data Query (PDO):

<?php
  // ... (Database connection) ...

  try {
    $sql = "SELECT id, isim, email FROM kullanicilar";
    $stmt = $conn->prepare($sql);
    $stmt->execute();

    // Get the results as an array
    $result = $stmt->fetchAll(PDO::FETCH_ASSOC);

    // Print the results to the screen
    foreach($result as $row) {
      echo "ID: " . $row["id"]. " - Name: " . $row["isim"]. " - Email: " . $row["email"]. "<br>";
    }
  } catch(PDOException $e) {
    echo "Query error: " . $e->getMessage();
  }

  $conn = null; // Close the connection
?>

Important Points:

• Store database connection information (server name, username, password, database name) securely.
• Take precautions against SQL injection attacks. Use parameterized queries (prepared statements).
• Close the database connection after you are finished.

Common PHP Errors and Solutions

Common errors and solutions encountered during the PHP development process are as follows:

• Syntax Errors: Misspelled keywords, missing semicolons, parenthesis errors, etc. Solution: Read the error message carefully and check the code on the specified line.
• Runtime Errors: Undefined variables, file not found errors, database connection errors, etc. Solution: Read the error message carefully and make sure that the relevant variable is defined, the file exists, or the database connection is correct.
• Logical Errors: The code runs correctly but does not produce the expected result. Solution: Examine the code step by step, check the values of the variables, and make sure the algorithm is correct. Use debugging tools.
• Security Vulnerabilities: Security vulnerabilities such as SQL injection, XSS (Cross-Site Scripting), CSRF (Cross-Site Request Forgery). Solution: Take security measures (e.g., use parameterized queries, validate user inputs, use CSRF tokens).
• Performance Issues: Slow running queries, unnecessary loops, unoptimized code, etc. Solution: Optimize the code, index the queries, use caching mechanisms.

Debugging Methods:

• error_reporting() and display_errors: Enable error reporting.
• var_dump() and print_r(): Print the values of variables to the screen.
• die() or exit(): Stop the code from running at a specific point and check the values of variables.
• Debugging Tools: Use debugging tools like Xdebug.

Example Error Scenario:

Error: "Undefined variable $isim" error.

Reason: The $isim variable is being used without being defined.

Solution: Define the variable before using it (e.g., $isim = "Ahmet";).

What are the Differences Between PHP Versions?

There are significant performance, security, and feature differences between different versions of PHP. Here are some important versions and their differences:

• PHP 5.x: These are old versions that are no longer supported. They may contain security vulnerabilities.
• PHP 7.x: Offers significant performance improvements and new features compared to PHP 5. For example, scalar type declarations, null coalescing operator (??), etc.
• PHP 8.x: Includes even more performance improvements, new features, and syntax changes compared to PHP 7. For example, JIT (Just-In-Time) compiler, union types, named arguments, etc.

Comparison of PHP Versions (Table):

Important Points:

• Always try to use the latest stable PHP version.
• Avoid using old versions as they may contain security vulnerabilities.
• Test your application before migrating to new versions.

PHP's development is constantly evolving. This document is an introduction to the world of PHP. It is recommended to review the official PHP documentation and community resources for more in-depth information and to keep up with current developments. Remember, continuous learning and practice are important to become a successful web developer. If you need professional support during your web development process, you can get help from companies that offer Web Software Services.