🔹 Basic PHP Interview Questions

1. What is PHP?

   • Answer: PHP (Hypertext Preprocessor) is a widely-used, open-source server-side scripting language specifically suited for web development and can be embedded into HTML.

2. What are the differences between echo and print in PHP?

   • Answer: echo can output one or more strings and is slightly faster; print can only output one string and always returns 1, so it can be used in expressions.

3. What are the common data types in PHP?

   • Answer: PHP supports data types like string, integer, float, boolean, array, object, NULL, and resource.

4. How do you define a constant in PHP?

   • Answer: define("SITE_NAME", "MyWebsite"); or using const SITE_NAME = "MyWebsite"; (inside classes or global scope in PHP 5.3+).

5. How are variables declared in PHP?

   • Answer: All variables in PHP start with the dollar sign $, e.g., $name = "John";.

🔹 Intermediate PHP Interview Questions

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

   • Answer: GET appends data to the URL and is suitable for retrieving data, while POST sends data in the request body and is used for secure data submission (like forms).

7. Explain the difference between == and === in PHP.

   • Answer: == compares values regardless of type, while === compares both value and type.

8. What is a session in PHP?

   • Answer: A session stores user data to be used across multiple pages (using $_SESSION), and it persists until the user closes the browser or session is destroyed.

9. What are cookies in PHP?

   • Answer: Cookies are small files stored on the client-side using setcookie() and are used to track and identify returning users.

10. How can you connect to a MySQL database using PHP?

    • Answer:

$conn = new mysqli("localhost", "username", "password", "database");
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

🔹 Advanced PHP Interview Questions

11. What are traits in PHP?

• Answer: Traits allow code reuse in single inheritance languages like PHP by including methods into a class, helping to avoid duplication.

12. Explain PDO in PHP.

• Answer: PDO (PHP Data Objects) provides a consistent interface for accessing databases securely and supports prepared statements, which help prevent SQL injection.

13. What is the difference between include(), require(), include_once(), and require_once()?

• Answer:

  • include() emits a warning if the file is missing, script continues.

  • require() gives a fatal error, script stops.

  • *_once() versions ensure the file is included only once.

14. What is Composer in PHP?

• Answer: Composer is a dependency manager for PHP, allowing you to manage libraries and project dependencies easily using composer.json.

15. How do you handle errors in PHP?

• Answer: By using try-catch blocks for exceptions and setting custom error handlers using set_error_handler().