Mastering PHP
Set 1
Key Interview Questions and Answers for Students
1. What
is PHP?
Answer:
PHP (Hypertext Preprocessor) is a server-side scripting language primarily used
for web development. It can be embedded into HTML to create dynamic web pages.
PHP is open-source and can be run on various platforms (Windows, Linux, etc.).
2. Explain
the difference between == and === in PHP.
Answer:
- ==
is the equality operator in PHP, which checks if two variables have the
same value, but it ignores data type.
- ===
is the strict equality operator, which checks both the value and the data
type of two variables.
Example:
$a = 10;
$b = "10";
var_dump($a
== $b); // true (values are the same)
var_dump($a
=== $b); // false (different data types)
3. What
are the different types of errors in PHP?
Answer:
PHP has four types of errors:
- Parse
Error (Syntax Error): Occurs when there is a syntax mistake in the
PHP code.
- Fatal
Error: A severe error that causes PHP to stop
executing the script (e.g., calling a non-existent function).
- Warning:
Non-fatal errors, PHP will continue executing the script (e.g., including
a file that does not exist).
- Notice:
Minor errors indicating something that might lead to an issue (e.g.,
undefined variable usage).
4. What
are sessions in PHP?
Answer:
A session is a way to store user information (variables) to be used across
multiple pages. Unlike cookies, session data is stored on the server and can be
accessed using a unique session ID. PHP provides session_start() to initialize
a session and session_destroy() to end it.
Example:
session_start();
$_SESSION['username']
= "JohnDoe";
5. What
are cookies in PHP?
Answer:
A cookie is a small piece of data stored on the client’s computer to remember
information about the user. Cookies are sent along with HTTP requests. You can
set cookies using the setcookie() function in PHP.
Example:
setcookie("user",
"JohnDoe", time() + (86400 * 30), "/"); // Expires in 30
days
6. Explain
the difference between include and require in PHP.
Answer:
- include: If
the specified file is not found, PHP will issue a warning but continue
executing the script.
- require: If
the specified file is not found, PHP will issue a fatal error and stop the
execution of the script.
7. What
is the use of mysqli_connect() in PHP?
Answer:
The mysqli_connect() function is used to establish a connection to a MySQL
database. It requires parameters like the hostname, username, password, and
database name.
Example:
$conn = mysqli_connect("localhost",
"root", "password", "mydatabase");
if (!$conn)
{
die("Connection
failed: " . mysqli_connect_error());
}
8. What
is the difference between mysql_query() and mysqli_query()?
Answer:
- mysql_query()
is part of the old mysql extension, which is deprecated and no longer
supported in recent PHP versions.
- mysqli_query()
is part of the newer mysqli extension, which supports prepared statements,
transactions, and better error handling.
9. What
are Prepared Statements in PHP?
Answer:
Prepared statements are used to execute SQL queries in a way that prevents SQL
injection. It involves preparing a query with placeholders for user input and
then binding the actual values.
Example:
$stmt = $conn->prepare("SELECT
* FROM users WHERE username = ?");
$stmt->bind_param("s",
$username);
$username
= 'john';
$stmt->execute();
10. What
is the difference between GET and POST methods in PHP?
Answer:
- GET:
Sends data via the URL, making it visible in the browser’s address bar. It
is generally used for retrieving data and should not be used for sensitive
information.
- POST:
Sends data via HTTP headers, making it more secure as data is not visible
in the URL. It is used to submit data like forms or files.
11. What
is MVC architecture in PHP?
Answer:
MVC (Model-View-Controller) is an architectural pattern used in PHP frameworks
(like Laravel, Symfony, etc.) to separate the application into three parts:
- Model:
Handles data and business logic.
- View:
Displays the data (user interface).
- Controller:
Handles the user input, updates the model, and renders the view.
12. What
is PDO in PHP?
Answer:
PDO (PHP Data Objects) is a database access library in PHP. It provides a
consistent interface for accessing different database systems and supports
features like prepared statements, transactions, and error handling.
Example:
$pdo = new
PDO('mysql:host=localhost;dbname=test', 'root', '');
$stmt = $pdo->prepare("SELECT
* FROM users");
$stmt->execute();
$result =
$stmt->fetchAll();
13. How
does PHP handle file uploads?
Answer:
PHP provides the $_FILES superglobal to handle file uploads. The move_uploaded_file()
function can be used to move the uploaded file to a designated directory.
Example:
if ($_FILES['file']['error']
== 0) {
move_uploaded_file($_FILES['file']['tmp_name'],
'uploads/' . $_FILES['file']['name']);
}
14. What
is the use of the isset() function in PHP?
Answer:
The isset() function checks whether a variable is set and is not NULL. It
returns true if the variable exists and has a value other than NULL.
Example:
if (isset($username))
{
echo "Username is set";
}
15. What
is a namespace in PHP?
Answer:
A namespace in PHP is used to group logically related classes, functions, and
constants. It helps to avoid name conflicts when different libraries or
codebases use the same names.
Example:
namespace
MyNamespace;
class MyClass
{
public function sayHello() {
echo "Hello from MyClass!";
}
}
16. What
is the difference between require and require_once in PHP?
Answer:
- require:
Includes the specified file every time it is called.
- require_once:
Includes the specified file only once, even if it is called multiple
times, helping to avoid redeclaration errors.
17. What
is the use of header() function in PHP?
Answer:
The header() function is used to send raw HTTP headers to the browser. It is
commonly used for redirecting pages or setting content type.
Example:
header("Location:
http://example.com");
exit();
18. What
is an Autoloader in PHP?
Answer:
An autoloader is a mechanism in PHP that automatically loads classes when they
are needed, instead of requiring explicit include or require statements. The spl_autoload_register()
function registers an autoloader function.
Example:
spl_autoload_register(function
($class) {
include $class . '.class.php';
});
19. What
is Composer in PHP?
Answer:
Composer is a dependency management tool for PHP. It is used to manage
libraries, packages, and dependencies in a PHP project. Composer helps to
automatically download and install required libraries and autoload them.
20. What
are Traits in PHP?
Answer:
A trait is a mechanism for code reuse in PHP. Traits allow developers to define
methods that can be included in multiple classes without using inheritance.
Example:
trait Logger
{
public function log($message) {
echo $message;
}
}
class MyClass
{
use Logger;
}