Top PHP interview questions

Are you preparing for an interview as a PHP developer and want to review your knowledge and abilities? Being well-prepared is essential for securing a great interview, regardless of your experience level as a PHP developer or your recent entry into the field. 

One of the most popular server-side scripting languages for creating dynamic web applications is still PHP (Hypertext Preprocessor). Learning PHP gives you access to a wide range of job options in the tech sector thanks to its vibrant ecosystem of frameworks, libraries, and tools. 

We'll go over a carefully chosen list of PHP interview questions in this blog post, which is intended to assess your knowledge of important ideas, adherence to best practices, and aptitude for solving problems. Let's get started and give you the tools you need to ace your PHP interviews!

1. Is PHP a case sensitive language?
Not fully. PHP is partly a case sensitive language where the variable names are case-sensitive but function names are not. Also, user-defined functions aren’t case sensitive but the rest of the language is.

2. What are the popular frameworks in PHP?
Laravel
CakePHP
CodeIgniter
Symfony
Zend Framework
Yii 2

3. Name the popular Content Management Systems (CMS) in PHP?
WordPress
Joomla
Magento
Drupal

4. What is the difference between static and dynamic websites?
Static websites are stored in a file system and served as is to the user. These websites are not dynamic and cannot be changed without manually editing the files on the server. On the other hand, dynamic websites are content-rich and can be altered based on various external factors. For example, content may be changed on the fly based on user input, or the content may be generated with the help of a database.

5. What is NULL?
NULL is a particular type of value in PHP. It represents a variable with no value and is usually used to denote the absence of a deal.

6. How do you define a constant in PHP?
A constant is a value in PHP that cannot be changed once it has been defined. Constants are defined using the define() function, which takes two arguments: the name of the constant and the value to assign it.

define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.

7. What are the differences between PHP constants and variables?
One of the most significant differences between PHP constants and variables is their scope. In PHP, constants are global, meaning they are accessible in all parts of an application, while variables are generally only accessible in the area where they were declared. Additionally, constants must be explicitly defined before they can be used, while variables can be said without initializing them.

8. What is the purpose of the break and continue statement?
Break and continue statements are two fundamental concepts of programming. A break statement is used to terminate a loop or switch statement immediately. In contrast, a continue statement is used to skip the current iteration of the loop and continue with the next iteration.

9.How can you compare objects in PHP?
Comparing objects in PHP is a valuable way to determine if two things are equal. The comparison is made based on the properties of the object and the values of those properties. PHP offers a built-in function for comparing objects called var_dump().

10. What are constructors and destructors in PHP?
Constructors and destructors are two essential concepts in the PHP language. A constructor is a particular method automatically called when an object is created. This process allows the thing to initialize any necessary data and perform any setup required before use.

11. What is the main difference between require() and require_once()?
require(), and require_once() basically perform the same task. The difference is that the latter checks whether the PHP script is already included or not before executing it.

12. What is the primary difference between include_once() and include()?
include(), and include_once() basically perform the same task. The difference is that the latter checks whether the PHP script is already included or not before executing it.

13. What is a session in PHP?
A session in PHP is a way to store information to be used across multiple pages of an entire website. The information is not stored on the user’s computer, unlike cookies. In a temporary directory on the server, a file will be created by the session where registered session variables and their values are stored. This information will be available to all pages on the site during that visit.

14. Explain the difference between $message and $$message?
$message is a regular variable. It has a fixed name and stores a fixed value. Data stored in $message is fixed.
$$message is a reference variable. It stores data about the variable. The value of the $$message can change dynamically as the value of the variable changes.

15. What are the data types supported by PHP?
There are 8 primary data types in PHP which are used to construct the variables. They are:
- Integers: Integers are whole numbers without a floating-point. Ex: 1253.
- Doubles: Doubles are floating-point numbers. Ex: 7.876
- Booleans: It represents two logical states- true or false.
- NULL: NULL is a special type that only has one value, NULL. When no value is assigned to a variable, it can be assigned with NULL.
- Arrays: Array is a named and ordered collection of similar type of data. Ex: $colors = array("red", "yellow", "blue");
Strings: Strings are a sequence of characters. Ex: “Hello InterviewBit!”
- Resources: Resources are special variables that consist of references to resources external to PHP(such as database connections).
- Objects: An instance of classes containing data and functions. Ex: $mango = new Fruit();

16. What is the difference between “echo” and “print” in PHP?
echo - echo can output one or more strings. echo is faster than print because it does not return any value. If you want to pass more than one parameter to echo, a parenthesis should be used.

print - print can only output one string and it always returns 1. print is slower compared to echo. Use of parenthesis is not required with the argument list.

17. Explain the difference between include() and require()?
include - includes a file and throws a warning if the file was not found.

require - includes a file and throws a fatal error if the file was not found.

18. How do you define a variable in PHP?
A variable in PHP is the name of the memory location that holds data. In PHP, a variable is declared using the $ sign followed by the variable name.

19. Explain the difference between == and === in PHP?
== Operator: This operator is used to check the given values are equal or not. If yes, it returns true, otherwise it returns false.

=== Operator: This operator is used to check the given values and its data type are equal or not. If yes, then it returns true, otherwise it returns false.

20. Explain the use of the mysqli extension in PHP?
The mysqli extension (MySQL Improved) in PHP provides an interface to interact with MySQL databases. It offers an object-oriented approach and improved features over the older mysql extension.

21. What is the difference between GET and POST methods in form submissions?
The GET method is limited to a maximum number of characters, while the POST method has no such limitation. This is because the GET method sends data through the resource URL, which is limited in length, while the POST method sends data through the HTTP message body, which has no such limitation.

22. How do you handle sessions in PHP?
To start a session in PHP, you use the session_start() function. This function should be called at the beginning of every page where you want to use session variables.

You can set session variables by assigning values to $_SESSION array elements.

23. What is the purpose of the header() function in PHP?
The **header()** function in PHP is used to send HTTP headers to the client's browser before any actual output is sent. This function is primarily used for redirection, setting cookies, controlling caching, and other HTTP header-related tasks. It allows developers to manipulate HTTP headers, which are important for controlling the behavior of web pages and web applications.

For example, you can use the **header()** function to redirect the user to another page by sending

header("Location: https://www.example.com");
?>

24. Explain the concept of cookies in PHP?
A cookie is a tiny file placed on the user's machine by the server. The cookie will be sent each time the same machine requests a page via a browser. Cookie values can be created and retrieved using cookies in PHP. Cookies are text files that are saved on the client computer for the purpose of monitoring.

25. How can you prevent SQL injection in PHP?
to avoid SQL injection is by binding all data via prepared statements. Using parameterized queries isn't enough to entirely avoid SQL injection, but it is the easiest and safest way to provide input to SQL statements.

26. How can you pass data between pages in PHP?
Session, Cookies, post, get

27. What is the ternary operator in PHP, and how is it used?
The ternary operator in PHP is a shorthand way of writing an if-else statement. It allows you to write concise conditional expressions with a single line of code. 
(condition) ? true_expression : false_expression;

28. How do you handle file uploads in PHP?
Handling file uploads in PHP involves using the $_FILES superglobal to access information about the uploaded file and moving the uploaded file from the temporary directory to a destination directory on the server.

29. What is the difference between unset() and unlink() functions in PHP?
The unset() function is used to unset or destroy a variable. 
unlink() function is used to delete a file from the file system

30. difference between for loop and foreach loop?
Use for loops for general-purpose looping or when you need more control over the loop counter.

Use foreach loops for iterating over collections when you only need to process each item and don't need to modify the collection structure.

Armed with these PHP interview questions and answers, you're well-prepared for your upcoming interviews. Remember to review and practice each question thoroughly. Good luck, and may your expertise shine in your PHP developer journey!