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PHP Interview Questions and Answers

Top 100 PHP Interview Questions for Freshers

PHP is one of the most widely used server-side scripting languages in web development, enabling developers to create dynamic, interactive, and scalable web applications. Mastering PHP allows professionals to build feature-rich websites, content management systems, e-commerce platforms, and RESTful APIs.Candidates should be well-prepared to tackle both the PHP Online Assessment and Technical Interview Round at IDM TechPark.To help you succeed, we have compiled a list of the Top 100 PHP Interview Questions along with their answers. Mastering these concepts will give you a strong edge in cracking PHP interviews and excelling in web development roles.

1. What is PHP?

Answer: PHP (Hypertext Preprocessor) is an open-source, server-side scripting language used for web development to create dynamic and interactive websites.

2. What are the key features of PHP?

Answer:

Open-source and free
Cross-platform compatibility
Supports multiple databases (MySQL, PostgreSQL, SQLite)
Loosely typed and easy to learn
Built-in security functions
Supports object-oriented programming (OOP)

3. What are PHP variables?

Answer:
Variables in PHP are used to store data and start with a $ sign.

Example:

$name = "John"; $age = 25;

4. What are PHP data types?

Answer:

String
Integer
Float
Boolean
Array
Object
NULL
Resource

5. How do you write comments in PHP?

Answer:

// Single-line comment # Another single-line comment /* Multi-line comment */

6. What is the difference between echo and print?

Answer:

echo can output multiple strings and is slightly faster.
print returns 1 and is slower as it can only print a single string.

Example:

echo "Hello", " World"; print "Hello World";

7. What is the difference between single (') and double (") quotes in PHP?

Answer:

Single quotes (') treat content as plain text.
Double quotes (") process variables inside the string.

Example:

$name = "Alice"; echo 'Hello $name'; // Output: Hello $name echo "Hello $name"; // Output: Hello Alice

8. What is the use of the isset() function?

Answer:
It checks if a variable is set and not NULL.

Example:

$var = "Hello"; echo isset($var); // Output: 1 (true)

9. What is the use of the empty() function?

Answer:
It checks if a variable is empty or not.

Example:

$var = ""; echo empty($var); // Output: 1 (true)

10. How do you define a constant in PHP?

Answer:
Using the define() function or const keyword.

Example:

define("SITE_NAME", "MyWebsite"); const PI = 3.14;

11. What is the difference between == and === in PHP?

Answer:

== checks for value equality.
=== checks for value and data type equality.

Example:

$a = 5; $b = "5"; echo ($a == $b); // Output: 1 (true) echo ($a === $b); // Output: (false)

12. How do you create an array in PHP?

Answer:

$fruits = array("Apple", "Banana", "Cherry"); $numbers = [1, 2, 3, 4];

13. How do you loop through an array in PHP?

Answer:
Using foreach loop.

$fruits = ["Apple", "Banana", "Cherry"]; foreach ($fruits as $fruit) { echo $fruit; }

14. What is the difference between include and require?

Answer:

include gives a warning if the file is missing, but the script continues.
require stops the script execution if the file is missing.

Example:

include "file.php"; require "file.php";

15. What is the difference between GET and POST methods?

Answer:

GETPOST

Data is sent in the URLData is sent in the request body

Less secureMore secure

Used for retrieving dataUsed for submitting data

Example:

$_GET['name']; $_POST['name'];

16. How do you handle form data in PHP?

Answer:
Using $_GET or $_POST.

$name = $_POST['name'];

17. What are PHP superglobals?

Answer:
Built-in global arrays:

$_GET, $_POST (Form data)
$_SESSION, $_COOKIE (User sessions)
$_FILES (File uploads)
$_SERVER (Server information)
$_REQUEST (Combination of $_GET, $_POST, $_COOKIE)

18. What is a session in PHP?

Answer:
A session stores user data across multiple pages.

Example:

session_start(); $_SESSION["username"] = "John";

19. What is a cookie in PHP?

Answer:
A cookie stores small amounts of data in the user’s browser.

Example:

setcookie("user", "John", time() + (86400 * 30), "/");

20. How do you connect PHP to a MySQL database?

Answer:
Using mysqli_connect() or PDO.

Example:

$conn = mysqli_connect("localhost", "root", "", "database_name");

21. How do you perform CRUD operations in PHP?

Answer:
Using SQL queries:

mysqli_query($conn, "INSERT INTO users (name) VALUES ('John')");

22. What is the difference between mysql_* and mysqli_* functions?

Answer:

mysql_* (deprecated) does not support prepared statements.
mysqli_* supports security features like prepared statements.

Example using mysqli:

$conn = mysqli_connect("localhost", "root", "", "db"); $stmt = $conn->prepare("SELECT * FROM users WHERE id = ?"); $stmt->bind_param("i", $id); $stmt->execute();

23. What is PDO in PHP?

Answer:
PDO (PHP Data Objects) is a database connection abstraction layer that supports multiple databases.

Example:

$pdo = new PDO("mysql:host=localhost;dbname=mydb", "root", "");

24. How do you redirect a user in PHP?

Answer:
Using header() function.

header("Location: home.php"); exit();

25. How do you handle errors in PHP?

Answer:
Using try-catch for exception handling.

try { throw new Exception("Error occurred!"); } catch (Exception $e) { echo $e->getMessage(); }

1. What is the difference between require_once and include_once?

Answer:

require_once includes a file only once and stops execution if the file is missing.
include_once includes a file only once but gives a warning if the file is missing.

Example:

require_once "config.php"; include_once "header.php";

2. How does PHP handle type juggling?

Answer:
PHP automatically converts data types based on the context.

Example:

$x = "10" + 5; // PHP converts "10" to an integer echo $x; // Output: 15

3. How do you prevent SQL injection in PHP?

Answer:
Using prepared statements.

Example:

$conn = new mysqli("localhost", "user", "password", "database"); $stmt = $conn->prepare("SELECT * FROM users WHERE email = ?"); $stmt->bind_param("s", $email); $stmt->execute();

4. What are magic methods in PHP?

Answer:
Special functions that start with __ (double underscore), such as:

__construct() – Constructor
__destruct() – Destructor
__get() – Getter
__set() – Setter
__toString() – Converts an object to a string

Example:

class Person { public $name; public function __construct($name) { $this->name = $name; } public function __toString() { return $this->name; } } $p = new Person("Alice"); echo $p; // Output: Alice

5. What is the difference between explode() and implode()?

Answer:

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

Example:

$str = "apple,banana,orange"; $arr = explode(",", $str); // Convert string to array $joined = implode("-", $arr); // Convert array to string

6. What is a namespace in PHP?

Answer:
A namespace avoids name conflicts in large applications.

Example:

namespace MyApp; class User {}

7. What are traits in PHP?

Answer:
Traits allow code reusability in multiple classes without inheritance.

Example:

trait Logger { public function log($msg) { echo $msg; } } class User { use Logger; } $user = new User(); $user->log("Hello!");

8. What is the difference between public, private, and protected in PHP?

Answer:

public – Accessible from anywhere.
private – Accessible only within the class.
protected – Accessible within the class and subclasses.

Example:

class Test { public $a = 1; private $b = 2; protected $c = 3; }

9. What is the difference between isset() and empty()?

Answer:

isset() checks if a variable is set and not NULL.
empty() checks if a variable is empty (0, "", NULL, false).

Example:

$var = ""; isset($var); // true empty($var); // true

10. How do you handle file uploads in PHP?

Answer:

move_uploaded_file($_FILES["file"]["tmp_name"], "uploads/" . $_FILES["file"]["name"]);

11. What is the difference between session_unset() and session_destroy()?

Answer:

session_unset() clears all session variables.
session_destroy() destroys the session completely.

Example:

session_start(); session_unset(); session_destroy();

12. What is the difference between serialize() and json_encode()?

Answer:

serialize() converts PHP objects to a storable string format.
json_encode() converts PHP data to a JSON string.

Example:

$data = ["name" => "Alice", "age" => 25]; $json = json_encode($data); // {"name":"Alice","age":25}

13. What are PHP filters?

Answer:
PHP filters are used for input validation and sanitization.

Example:

$email = filter_var("test@example.com", FILTER_VALIDATE_EMAIL);

14. What is PDO and why is it used?

Answer:
PDO (PHP Data Objects) is a database abstraction layer supporting multiple databases.

Example:

$pdo = new PDO("mysql:host=localhost;dbname=test", "root", "");

15. What is cURL in PHP?

Answer:
cURL is used to make HTTP requests.

Example:

$ch = curl_init("https://example.com"); curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); $response = curl_exec($ch); curl_close($ch);

16. How do you create a session in PHP?

Answer:

session_start(); $_SESSION["user"] = "John";

17. What are cookies in PHP?

Answer:
Cookies store user data in the browser.

Example:

setcookie("user", "John", time() + 3600, "/");

18. How do you execute a PHP script from the command line?

Answer:

php script.php

19. How do you send an email using PHP?

Answer:
Using mail() function.

mail("to@example.com", "Subject", "Message", "From: from@example.com");

20. How do you redirect a page in PHP?

Answer:

header("Location: home.php"); exit();

21. What is htaccess in PHP?

Answer:
A configuration file used to control website settings.

Example: Redirect HTTP to HTTPS

RewriteEngine On RewriteCond %{HTTPS} off RewriteRule ^(.*)$ https://%{HTTP_HOST}/$1 [R=301,L]

22. What is ob_start() in PHP?

Answer:
Starts output buffering.

Example:

ob_start(); echo "Hello"; $output = ob_get_clean();

23. What is unlink() in PHP?

Answer:
Deletes a file.

unlink("file.txt");

24. What is the use of debug_backtrace()?

Answer:
Provides a stack trace of function calls.

Example:

print_r(debug_backtrace());

25. How do you handle errors in PHP?

Answer:
Using set_error_handler().

function errorHandler($errno, $errstr) { echo "Error: $errstr"; } set_error_handler("errorHandler");

Conclusion

These 25 Intermediate PHP Questions cover core PHP concepts. Let me know if you need Advanced or Technical PHP Interview Questions! 🚀

1. What are anonymous functions (closures) in PHP?

Answer:
Anonymous functions, also known as closures, are functions without names. They are useful for callbacks and functional programming.

Example:

$greet = function($name) { return "Hello, $name!"; }; echo $greet("Alice"); // Output: Hello, Alice!

2. What is the difference between static and final keywords in PHP?

Answer:

static allows properties and methods to belong to the class instead of instances.
final prevents a class from being extended or a method from being overridden.

Example:

class A { final public function sayHello() { echo "Hello"; } } class B extends A { // Cannot override sayHello() because it's final }

3. How do you handle transactions in PHP with MySQL?

Answer:
Using PDO transactions.

$pdo->beginTransaction(); $pdo->exec("INSERT INTO users (name) VALUES ('Alice')"); $pdo->commit();

4. How do you implement dependency injection in PHP?

Answer:
Dependency injection helps manage dependencies externally.

Example:

class Database { public function connect() { echo "Connected"; } } class User { private $db; public function __construct(Database $db) { $this->db = $db; } } $db = new Database(); $user = new User($db);

5. What is the SPL (Standard PHP Library)?

Answer:
SPL provides built-in classes and interfaces for common programming tasks (e.g., iterators, exception handling).

Example using ArrayIterator:

$array = new ArrayIterator(["A", "B", "C"]); foreach ($array as $item) { echo $item; }

6. What is autoloading in PHP?

Answer:
Autoloading automatically loads classes when they are needed.

Example:

spl_autoload_register(function($class) { include $class . '.php'; }); $obj = new MyClass(); // Auto-includes "MyClass.php"

7. How do you implement method chaining in PHP?

Answer:
Returning $this allows method chaining.

Example:

class Car { public function start() { echo "Start "; return $this; } public function drive() { echo "Drive "; return $this; } } $car = new Car(); $car->start()->drive(); // Output: Start Drive

8. What is the difference between invoke() and call()?

Answer:

__invoke() allows an object to be called like a function.
__call() handles calls to undefined methods.

Example:

class Test { public function __invoke($x) { return $x * 2; } } $obj = new Test(); echo $obj(5); // Output: 10

9. How do you use generators in PHP?

Answer:
Generators yield values instead of returning them all at once.

Example:

function numbers() { for ($i = 1; $i <= 3; $i++) { yield $i; } } foreach (numbers() as $num) { echo $num; }

10. What is the difference between yield and return?

Answer:

yield allows iteration over large datasets without memory overload.
return exits a function immediately.

11. How do you create an immutable class in PHP?

Answer:
By preventing property modification.

Example:

class Immutable { private $value; public function __construct($value) { $this->value = $value; } public function getValue() { return $this->value; } } $obj = new Immutable(10);

12. What is weak typing in PHP?

Answer:
PHP dynamically converts data types as needed.

Example:

$x = "5" + 2; // Output: 7

13. What are PHP fibers?

Answer:
Fibers allow asynchronous programming in PHP 8.1.

Example:

$fiber = new Fiber(function() { return "Hello"; }); echo $fiber->start();

14. How do you optimize PHP performance?

Answer:

Use OPcache
Use CDN for assets
Minimize database queries
Optimize loops and algorithms

15. How do you store objects in a session?

Answer:
Using serialize().

session_start(); $_SESSION['user'] = serialize(new User("Alice"));

16. What is the difference between json_encode() and serialize()?

Answer:

json_encode() is human-readable and cross-language compatible.
serialize() is PHP-specific and can handle complex data structures.

17. How do you handle large file uploads in PHP?

Answer:

Increase upload_max_filesize and post_max_size in php.ini.

Example:

upload_max_filesize = 50M post_max_size = 50M

18. What are E_STRICT and E_DEPRECATED errors?

Answer:

E_STRICT: Enforces best practices.
E_DEPRECATED: Warns about outdated features.

19. How do you create custom exceptions in PHP?

Answer:
Using the Exception class.

Example:

class MyException extends Exception {} throw new MyException("Error occurred!");

20. What is fastcgi_finish_request()?

Answer:
Sends a response to the client while PHP continues executing in the background.

Example:

echo "Response sent!"; fastcgi_finish_request(); // Background tasks continue...

21. How do you prevent XSS (Cross-Site Scripting) in PHP?

Answer:
Use htmlspecialchars().

echo htmlspecialchars("<script>alert('XSS');</script>");

22. What is the Reflection API in PHP?

Answer:
The Reflection API allows runtime analysis of classes and methods.

Example:

$reflect = new ReflectionClass('User'); print_r($reflect->getMethods());

23. How do you implement memoization in PHP?

Answer:
Caching function results.

Example:

function memoize($func) { static $cache = []; return function($arg) use ($func, &$cache) { return $cache[$arg] ?? ($cache[$arg] = $func($arg)); }; }

24. How do you prevent CSRF in PHP?

Answer:
Use CSRF tokens in forms.

Example:

$_SESSION['csrf_token'] = bin2hex(random_bytes(32));

25. How do you work with Callable in PHP?

Answer:
Callable allows passing functions as parameters.

Example:

function execute(callable $func) { return $func(); } execute(function() { return "Hello"; });

1. What are the different PHP error types?

Answer:

E_ERROR – Fatal runtime errors.
E_WARNING – Run-time warnings (non-fatal).
E_NOTICE – Minor run-time notices.
E_PARSE – Compilation-time syntax errors.

Example:

error_reporting(E_ALL); // Display all errors

2. How do you enable debugging in PHP?

Answer:
Use error_reporting() and display_errors.

ini_set('display_errors', 1); error_reporting(E_ALL);

3. What is the difference between require and include?

Answer:

require: Generates a fatal error if the file is missing.
include: Generates a warning but continues execution.

Example:

require 'config.php'; include 'header.php';

4. What is the purpose of the php.ini file?

Answer:
php.ini is the configuration file for PHP. It controls settings like:

memory_limit
max_execution_time
upload_max_filesize

Example:

memory_limit = 512M upload_max_filesize = 50M

5. What are PHP superglobals?

Answer:
Superglobals are predefined variables:

$_GET, $_POST – Form data
$_SERVER – Server details
$_SESSION, $_COOKIE – User session management
$_FILES – File uploads

6. How do you prevent SQL injection in PHP?

Answer:
Use prepared statements.

$stmt = $pdo->prepare("SELECT * FROM users WHERE email = ?"); $stmt->execute([$email]);

7. What is the difference between isset(), empty(), and is_null()?

Answer:

isset($var): Returns true if the variable is set and not null.
empty($var): Returns true if the variable is empty ("", 0, false, null).
is_null($var): Returns true if the variable is null.

8. How do you handle file uploads securely in PHP?

Answer:

Validate file type
Limit file size
Store files outside the web root

Example:

if ($_FILES['file']['size'] < 1048576) { // 1MB limit move_uploaded_file($_FILES['file']['tmp_name'], 'uploads/' . $_FILES['file']['name']); }

9. How do you create and destroy a PHP session?

Answer:

session_start(); // Start session $_SESSION['user'] = 'Alice'; // Set session session_destroy(); // Destroy session

10. What is the difference between session_unset() and session_destroy()?

Answer:

session_unset(): Clears all session variables.
session_destroy(): Destroys the session but keeps session variables.

11. What are traits in PHP?

Answer:
Traits allow code reuse in multiple classes without inheritance.

Example:

trait Logger { public function log($msg) { echo $msg; } } class User { use Logger; } $user = new User(); $user->log("Hello");

12. How do you implement authentication in PHP?

Answer:

Use password_hash() for storing passwords
Use sessions for login tracking

Example:

$password = password_hash('mysecret', PASSWORD_BCRYPT);

13. What is the difference between == and === in PHP?

Answer:

== checks value equality.
=== checks value and type equality.

Example:

var_dump(5 == "5"); // true var_dump(5 === "5"); // false

14. How does PHP handle garbage collection?

Answer:
PHP automatically frees memory of unreferenced variables using a garbage collector.

Example:

$var = null; gc_collect_cycles(); // Manually trigger garbage collection

15. How do you prevent XSS attacks in PHP?

Answer:
Use htmlspecialchars() to escape HTML characters.

Example:

echo htmlspecialchars("<script>alert('XSS');</script>");

16. What is a RESTful API in PHP?

Answer:
A RESTful API follows REST principles using HTTP methods (GET, POST, PUT, DELETE).

Example:

header('Content-Type: application/json'); echo json_encode(["message" => "Hello"]);

17. What is the difference between explode() and implode()?

Answer:

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

Example:

$arr = explode(",", "A,B,C"); // ["A", "B", "C"] $str = implode("-", $arr); // "A-B-C"

18. What are PHP streams?

Answer:
Streams provide an abstraction for file handling, network communication, and more.

Example:

$handle = fopen('file.txt', 'r');

19. How do you handle exceptions in PHP?

Answer:
Use try-catch blocks.

Example:

try { throw new Exception("Error occurred"); } catch (Exception $e) { echo $e->getMessage(); }

20. How does PHP implement MVC architecture?

Answer:

Model: Handles database interaction
View: Displays data to users
Controller: Manages business logic

Example:

class UserModel { public function getUser() { return "Alice"; } } class UserController { public function show() { return (new UserModel)->getUser(); } }

21. How do you optimize MySQL queries in PHP?

Answer:

Use indexes
Avoid **SELECT ***
Use LIMIT for pagination

Example:

SELECT name FROM users WHERE email = ? LIMIT 1;

22. How do you use cURL in PHP?

Answer:

$ch = curl_init("https://api.example.com"); curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); $response = curl_exec($ch); curl_close($ch);

23. How do you implement pagination in PHP?

Answer:

$limit = 10; $offset = ($page - 1) * $limit; $query = "SELECT * FROM users LIMIT $limit OFFSET $offset";

24. How do you implement WebSockets in PHP?

Answer:
Use Ratchet WebSocket library for real-time communication.

Example:

$server = new Ratchet\App('localhost', 8080); $server->run();

25. What is fastcgi_finish_request() used for?

Answer:
It sends a response to the client while PHP continues processing in the background.

Example:

echo "Processing request..."; fastcgi_finish_request(); // Background processing

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"Deep Concepts to Elevate Your Career"

This guide provides 100+ PHP Interview questions along with in-depth concepts to strengthen your expertise.

Download

PHP Interview Questions and Answers

Top 100 PHP Interview Questions for Freshers

2. What are the key features of PHP?

3. What are PHP variables?

4. What are PHP data types?

5. How do you write comments in PHP?

6. What is the difference between echo and print?

7. What is the difference between single (') and double (") quotes in PHP?

8. What is the use of the isset() function?

9. What is the use of the empty() function?

10. How do you define a constant in PHP?

11. What is the difference between == and === in PHP?

12. How do you create an array in PHP?

13. How do you loop through an array in PHP?

14. What is the difference between include and require?

15. What is the difference between GET and POST methods?

16. How do you handle form data in PHP?

17. What are PHP superglobals?

18. What is a session in PHP?

19. What is a cookie in PHP?

20. How do you connect PHP to a MySQL database?

21. How do you perform CRUD operations in PHP?

22. What is the difference between mysql_* and mysqli_* functions?

23. What is PDO in PHP?

24. How do you redirect a user in PHP?

25. How do you handle errors in PHP?

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This guide provides 100+ PHP Interview questions along with in-depth concepts to strengthen your expertise.

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