Top 50 PHP Interview Questions and Answer

PHP is a widely used programming language for web development. If you're preparing for a PHP job interview, having a strong grasp of key concepts is essential. In this article, we’ll explore the top 50 PHP interview questions and answers to help you confidently succeed in your next interview.

Q1. What is PHP?

Answer: PHP stands for Hypertext Preprocessor. It is an open-source, server-side scripting language designed for creating dynamic web pages.

Q2. What are the common uses of PHP?

Answer: PHP is commonly used for:

Server-side scripting
Command-line scripting
Creating dynamic websites
Interacting with databases (e.g., MySQL)
Building RESTful APIs

Q3. How do you declare a variable in PHP?

Answer: Variables are declared using the $ symbol, e.g., $name = "Waliullah";.

Q4. What are PHP data types?

Answer : PHP supports:

String
Integer
Float (Double)
Boolean
Array
Object
NULL
Resource

Q5. What is the difference between echo and print?

Answer:

echo: Outputs data, can take multiple parameters, no return value.
print: Outputs data, returns 1, works like a function.

Q6. How do you define a constant in PHP?

Answer: Using the define() function, e.g., define("SITE_NAME", "Shikshatech");.

Q7. What are PHP magic constants?

Answer: Special constants starting with double underscores, like:

__LINE__
__FILE__
__DIR__
__FUNCTION__
__CLASS__

Q8. What is the difference between == and ===?

Answer:

==: Compares values only.
===: Compares values and data types.

Q9. What are superglobals in PHP?

Answer:

Predefined global arrays like

$_POST,
$_GET,
$_SESSION,
$_COOKIE,
$_SERVER.

Q10. How to connect to a MySQL database using PHP?

Answer:

To connect to a MySQL database using PHP, you can use either the MySQLi (MySQL Improved) extension or PDO (PHP Data Objects). Here's how to do it both ways:

Using MySQLi (Object-Oriented Style)


<?php

$host = "localhost";
$username = "your_username";
$password = "your_password";
$database = "your_database";

// Create connection
$conn = new mysqli($host, $username, $password, $database);

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}
echo "Connected successfully";
?>


Using MySQLi (Procedural Style)

<?php
$host = "localhost";
$username = "your_username";
$password = "your_password";
$database = "your_database";

// Create connection
$conn = mysqli_connect($host, $username, $password, $database);

// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
echo "Connected successfully";
?>


Using PDO (Recommended for Flexibility and Security)

<?php
$host = 'localhost';
$db   = 'your_database';
$user = 'your_username';
$pass = 'your_password';
$charset = 'utf8mb4';

$dsn = "mysql:host=$host;dbname=$db;charset=$charset";

try {
    $pdo = new PDO($dsn, $user, $pass);
    // Set error mode to exception
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    echo "Connected successfully";
} catch (PDOException $e) {
    echo "Connection failed: " . $e->getMessage();
}
?>


Q11. What are GET and POST methods?

Answer: 

The GET and POST methods are two of the most common HTTP request methods used to send data between a client (usually a web browser) and a server.


 GET Method
Purpose: Retrieve data from the server.
How it works: Data is sent in the URL (as query string parameters).
Example URL:

https://example.com/search.php?query=books&page=2
Use cases:
Search forms
Bookmarkable/filterable pages
Characteristics:
Visible in the browser URL
Can be bookmarked and cached
Limited in length (typically ~2000 characters)
Not secure for sensitive data (like passwords)
 POST Method
Purpose: Submit data to the server (e.g., form data).
How it works: Data is sent in the body of the HTTP request.
Example:

    Submitting a form that creates a new user account.
Characteristics:
Data is not visible in the URL
Cannot be bookmarked
No size limit (practically much larger than GET)
More secure than GET for sensitive data (still should use HTTPS)
PHP Example
php

// Handling GET request
if ($_SERVER["REQUEST_METHOD"] == "GET") {
    $search = $_GET["search"];
    echo "You searched for: " . htmlspecialchars($search);
}

// Handling POST request
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $username = $_POST["username"];
    echo "Submitted username: " . htmlspecialchars($username);
}
Q12 . What is the difference between include and require?
Answer:
It is possible to insert the content of one PHP file into another PHP file (before the server executes it), with the include or require statement.
The include and require statements are identical, except upon failure:
require will produce a fatal error (E_COMPILE_ERROR) and stop the script
include will only produce a warning (E_WARNING) and the script will continue
So, if you want the execution to go on and show users the output, even if the include file is missing, use the include statement. Otherwise, in case of FrameWork, CMS, or a complex PHP application coding, always use the require statement to include a key file to the flow of execution. This will help avoid compromising your application's security and integrity, just in-case one key file is accidentally missing.
Including files saves a lot of work. This means that you can create a standard header, footer, or menu file for all your web pages. Then, when the header needs to be updated, you can only update the header include file.
Syntax
include 'filename';
or
require 'filename';

Q14. How to send a cookie in PHP?

Answer:

setcookie("user", "Waliullah", time()+3600);

15. What is the use of `isset()` and `empty()`?

Answer:

isset() checks if a variable is set and not null.
empty() checks if a variable is empty.

16. What are magic constants in PHP?

Answer: Constants like __LINE__, __FILE__, __DIR__, __FUNCTION__.

17. What is a trait in PHP?

Answer: A mechanism to reuse code in multiple classes without using inheritance.

18. What is a namespace in PHP?

Answer: Used to avoid name collisions in larger applications.

19. What are constructors and destructors in PHP?

Answer:

Constructor: __construct(), called when an object is created.
Destructor: __destruct(), called when the object is destroyed.

20. What is the difference between `array_merge()` and `+` operator on arrays?

Answer: array_merge() merges and reindexes, + keeps keys from the left array.

OOP in PHP

21. What is Object-Oriented Programming?

Answer: Programming model organized around objects rather than actions.

22. What are the pillars of OOP?

Answer: Encapsulation, Inheritance, Polymorphism, Abstraction.

23. What is the difference between class and object?

Answer: A class is a blueprint; an object is an instance of a class.

24. How to define a class and create an object?

Answer:


class Car { }
$myCar = new Car();

25. What is inheritance in PHP?

Answer: One class can inherit properties/methods from another class using extends.

26. What is the use of `final` keyword in PHP?

Answer: Prevents class or method from being extended or overridden.

27. What is an interface in PHP?

Answer: Defines a contract with method signatures that implementing classes must define.

28. What is an abstract class in PHP?

Answer: Cannot be instantiated; must be extended. Can contain both abstract and concrete methods.

29. What is method overloading in PHP?

Answer: PHP doesn’t support it directly but can be emulated via __call() magic method.

30. What is the difference between `public`, `private`, and `protected`?

Answer:

public: accessible anywhere.
protected: accessible in class and subclasses.
private: accessible only within the class.

🔹 Advanced PHP Interview Questions

31. What is the use of `PDO` in PHP?

Answer: PHP Data Objects - A secure and consistent way to access databases.

32. What is the difference between `mysql` and `mysqli`?

Answer: mysql is deprecated. mysqli supports prepared statements, OOP, etc.

33. What are prepared statements?

Answer: SQL statements that are compiled once and executed multiple times securely.

34. What is XSS and how to prevent it?

Answer: Cross-Site Scripting; use htmlspecialchars() to sanitize output.

35. What is CSRF and how to prevent it?

Answer: Cross-Site Request Forgery; use CSRF tokens in forms.

36. What are some common security practices in PHP?

Answer: Input validation, escaping output, using HTTPS, password hashing, session protection.

37. How do you hash passwords in PHP?

Answer:

$password = password_hash("secret", PASSWORD_DEFAULT);

38. How do you verify hashed passwords?

Answer:


password_verify("secret", $hashed_password);

39. What is Composer in PHP?

Answer: Dependency manager for PHP.

40. What are autoloaders in PHP?

Answer: Automatically load PHP classes using spl_autoload_register().

🔹 Miscellaneous PHP Questions

41. How to handle errors in PHP?

Answer: Using try-catch blocks and error handling functions like set_error_handler().

42. What are the types of errors in PHP?

Answer: Parse errors, Fatal errors, Warning, Notice.

43. What is output buffering?

Answer: Delays sending output to the browser using ob_start().

44. What is the difference between `unlink()` and `unset()`?

Answer:

unlink() deletes a file.
unset() destroys a variable.

45. What is the difference between `require_once` and `include_once`?

Answer: Both include files once, but require_once stops execution on failure.

46. How to redirect a page in PHP?

Answer:


header("Location: page.php");

47. What is the use of `explode()` and `implode()`?

Answer:

explode() splits a string into an array.
implode() joins array elements into a string.

48. What is the difference between `GET` and `POST` in form submission?

Answer: GET is visible in URL, POST is secure and doesn’t show data in the URL.

49. How to upload a file in PHP?

Answer: Using $_FILES with proper HTML form and move_uploaded_file().

50. What is the difference between `static` and non-static methods?

Answer: Static methods can be called without creating an instance of the class.