Basic PHP Interview Questions and Answers

1. What is PHP?
PHP (Hypertext Preprocessor) is a server-side scripting language designed for web development. It is widely used to create dynamic web pages and applications.

2. What are the main features of PHP?

• Open-source and free
• Server-side scripting
• Cross-platform compatibility
• Supports a wide range of databases
• Easy to learn and use
• Supports OOP (Object-Oriented Programming)

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

Feature
GET
POST

Data sent
Appended to URL
Sent in the request body

Data size
Limited (~2000 characters)
No significant limit

Security
Less secure
More secure for sensitive data

Usage
Data retrieval
Data submission and updates

4. How do you declare a variable in PHP?

$variable_name = "value";

5. What are sessions in PHP?
Sessions are a way to store data across multiple pages. PHP creates a unique session ID for each user, allowing data to be persisted on the server.

6. How do you start a session in PHP?

session_start();

7. Explain the difference between include() and require().

• include(): Generates a warning if the file is not found but continues execution.
• require(): Generates a fatal error and stops execution if the file is not found.

8. How can you connect to a MySQL database using PHP?
Using mysqli:

$conn = new mysqli($servername, $username, $password, $dbname);

9. What are PHP superglobals?
Superglobals are built-in variables that are always accessible in all scopes. Examples include: $_GET, $_POST, $_SESSION, $_COOKIE, $_SERVER, $_FILES, $_REQUEST, $_ENV.

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

• == (Equality): Checks if values are equal after type juggling.
• === (Identical): Checks if values and types are exactly the same.

Intermediate PHP Interview Questions and Answers
11. What is OOP in PHP?
Object-Oriented Programming (OOP) is a programming paradigm based on the concept of objects, which contain data and methods. PHP supports OOP principles like classes, objects, inheritance, encapsulation, and polymorphism.

12. How do you define a class in PHP?

<code><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Car</span> </span>{
    <span class="hljs-keyword">public</span> <span class="hljs-variable">$color</span>;

    <span class="hljs-keyword">public</span> <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">__construct</span>(<span class="hljs-params"><span class="hljs-variable">$color</span></span>) </span>{
        <span class="hljs-variable language_">$this</span>->color = <span class="hljs-variable">$color</span>;
    }

    <span class="hljs-keyword">public</span> <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">getColor</span>() </span>{
        <span class="hljs-keyword">return</span> <span class="hljs-variable language_">$this</span>->color;
    }
}</code>

13. How can you include external PHP files?
Using include() or require():

<code><span class="hljs-keyword">include</span>(<span class="hljs-string">'header.php'</span>);
<span class="hljs-keyword">require</span>(<span class="hljs-string">'config.php'</span>);</code>

14. What is a PHP trait?
A trait is a mechanism for code reuse in single inheritance languages like PHP. It allows you to include methods in multiple classes.

15. How does PHP handle errors?
PHP offers error types like notices, warnings, and fatal errors. Error handling can be done using functions like try-catch blocks with exceptions or setting custom error handlers.

Advanced PHP Interview Questions and Answers
16. What are PHP namespaces?
Namespaces are a way of encapsulating items such as classes, functions, and constants to avoid name conflicts.

17. Explain the concept of PDO in PHP.
PHP Data Objects (PDO) provide a consistent interface for accessing databases in PHP, supporting multiple database systems with prepared statements for security.

18. How do you perform data validation in PHP?
Using functions like filter_var(), regex, or custom validation logic to ensure data integrity before processing or storing.

19. What is the difference between echo and print?

• echo can output one or more strings and is slightly faster.
• print behaves like a function, returns 1, and can only output one string at a time.

20. How can you prevent SQL injection in PHP?
Using prepared statements with parameterized queries via PDO or mysqli.