PHP Interview Questions

Top PHP Programming Language Interview Questions

You need to interview a PHP developer because you have a position that has become available? It is not always easy to ask questions about a programming language when you are not a developer yourself. Just for you, we have collected on this page the most interesting interview questions to find a highly qualified PHP programmer, and their answers.

These PHP interview questions should help you in your developer recruitment process, although the best way to hire the best candidate for a programming position is to use online coding tests.

Before starting, here is a quick definition of the term PHP that should help you if you are not familiar with this language:

PHP stands for “Hypertext Preprocessor”. PHP is an HTML-embedded Web scripting language. This means PHP code can be inserted into the HTML of a Web page. When a PHP page is accessed, the PHP code is read or “parsed” by the server the page resides on. The output from the PHP functions on the page are typically returned as HTML code, which can be read by the browser. Because the PHP code is transformed into HTML before the page is loaded, users cannot view the PHP code on a page. This make PHP pages secure enough to access databases and other secure information.

Christensson, P., PHP Definition, techterms.com

 

php-candidate-interview

As Python, PHP is a back-end technology. Here are our 24 PHP interview questions:

PHP interview question #1

How do you proceed if you need to get a user’s IP address?”

This question shows the level of creativity of the developer, as there are many possibilities to find an IP address.  For example, we can use the script : $_SERVER[“REMOTE_ADDR”];

This is the fastest and most obvious answer, but a multitude of other solutions are possible.

PHP interview question #2

What are Traits made for?

Traits are an advanced feature of PHP, they allow to create reusable code in a language like PHP. A Trait cannot be generated by itself, the candidate must be familiar with the advanced functionalities of a programming language in which he or she will be required to work. Knowledge of these features is an important indication of the candidate’s familiarity with this language.

PHP interview question #3

Describe the three error types that exist in PHP.

Knowledge of error types is fundamental for any developer, especially those who use PHP. This knowledge allows the developer to understand where the errors come from in order to be able to fix them as well as possible.

Here the candidate must first list the error types and then explain them. He must say that there are three errors types: Notices, Warning and Fatal. Then, the candidate must explain that Notices are errors that occur when the error is simple and non-critical, while Warning is a more serious error. In both cases, these errors will not cause the script to stop running. The last error, called Fatal, is much more problematic since it causes the script to stop running.

PHP interview question #4

What’s new in PHP 8.0?

The main new features of PHP 8.0 will be the JIT (Just in Time compilation), consistent type erros for internal functions, fatal error for incompatible method signatures and arrays starting with a negative index

A candidate who knows how to answer this specific question proves that he is passionate about programming, and that he keeps up to date with the latest evolution of PHP.

PHP release history:

  • PHP 1.0 : 1995
  • PHP 2.0 : 1997
  • PHP 3.0 : 1998
  • PHP 4.0 : 2000
  • PHP 5.0 : 2005
  • PHP 6.0 : Abandoned version of PHP, never released
  • PHP 7.0 : 2015
  • PHP 8.0 : 2020/2021

PHP interview question #5

What do you think are the essential attributes that a PHP developer should have?

This job interview question is a classic one, but some answers are expected from a good PHP programmer.

These include logical reasoning, analytical thinking, perseverance, insatiable curiosity, rigor and abnegation.

Each of these qualities is evidence of the candidate’s ability to work as a PHP developer.

PHP interview question #6

What is the role of _construct() and _destruct() methods in a PHP class?

The answer to this interview question determines whether the candidate has any knowledge of object-oriented programming. All objects in the PHP language have construct and destruct methods built-in. The Constructor method is used each time a new class instance is created, it is then called to initialize the properties of this class. The destruct method does not accept any parameters.

PHP interview question #7

Can the value that was previously assigned to a constant change during script execution?

Answer : no. When a value has been assigned to a constant, it cannot change during the script execution.

PHP interview question #8

What is the difference between Unset() and unlink()?

Using unset() allows the developer to change the variable to an undefined state, while the unlink() command deletes the file that is sent from the system.

PHP interview question #9

Declare a function, which will only accept the word “Hello” as a parameter.

If the data entered matches what was requested, then the function will display “Hello”. Otherwise it will display “Bye”.

php-function-echo

This question is a very good opportunity to assess the candidate’s ability to declare functions.

PHP interview question #10

What do you think of the pair programming?

Pair programming is a new working method that consists of having two developers work together on the same workstation.

This way of working has not been adopted by all companies, and perhaps not by yours. However, thanks to this question, you will know if the PHP developer you are questioning is a team player.

PHP interview question #11

How to proceed in order to get the quantity of elements in an array?

Here, we are dealing with a rather basic interview question about arrays. Knowing how to extract data from an array is part of the basic knowledge for any properly trained junior developer.

If you’re not familiar with the term “array”, here’s a definition :

An array is a data structure that contains a group of elements. Typically these elements are all of the same data type, such as an integer or string. Arrays are commonly used in computer programs to organize data so that a related set of values can be easily sorted or searched.

For example, a search engine may use an array to store Web pages found in a search performed by the user. When displaying the results, the program will output one element of the array at a time. This may be done for a specified number of values or until all the values stored in the array have been output. While the program could create a new variable for each result found, storing the results in an array is much more efficient way to manage memory.

Christensson, P., Array Definition, techterms.com

The optimal answer here is to use the count () function.

PHP interview question #12

Could you name some PHP frameworks?

This question is a basic one: any competent PHP developer is able to name some frameworks written in PHP language.

During the interview, the interviewed candidate must mention at least three PHP frameworks among this list:

  • Laravel, a free, open-source, PHP web framework intended for the development of web applications following the MVC architectural pattern and based on Symfony. It’s the most popular PHP framework.
  • CodeIgniter, an open-source software rapid development web framework, used to build dynamic sites with PHP.
  • Symfony, a PHP web application framework and a set of reusable components and libraries. It is released under the MIT license.
  • CakePHP
  • FuelPHP
  • PHPixie
  • Phalcon
  • Slim
  • Zend Framework
  • Yii 2

PHP interview question #13

Why use Getters and Setters?

Getters and Setters are methods used to declare or get the value of a private variable. They allow data to be processed, reported and displayed. Within these methods, it is possible to process the data, which will then be assigned within a variable function.

PHP interview question #14

What is the difference between the functions include() and require()?

The first one, contrary to the second one, is used to ensure that a file is included within the script during its execution. The candidate can use a demonstration, in which we have for example five files, one.txt, two.txt and so on up to five. The files contain numbers from one to five (a number in each file).  

php-include-function

The compilation time has been included once in each file. On the other hand, if we make the decision to write require instead of the other command, we will get a fatal error.

Another difference between these two commands is that require always gives a fatal error if the requested file is missing, while include will simply display a warning, and continue to compile the code.

PHP interview question #15

What will be the output of this script?

php-echo

Answer: 21, 21

PHP interview question #16

The value of the input variable is 9,3,5,5,7,8. How do I get the sum of the numbers of this list?

Answer :

php-echo-array-sum-explode

The explode function is one of the most frequently used in PHP language, so it is very important to understand if the candidate masters this function.

PHP interview question #17

How many scope levels exist in the PHP language? Describe them.

This interview question shows that the future PHP developer understands the essence of programming and is not just typing code without thinking beforehand. Moreover, this issue is important from the standpoint of data security, which is a key issue in our time.

The candidate must mention here the three existing scope levels of PHP which are Private, Public and Protected, and explain that the first level is visible only in his own class, the second one is visible by any script performing accessing the class and the last one is visible only by the parent classes.

PHP interview question #18

Why should you use === and not ==?

=== and == are two PHP comparison operators.

First of all ==== is faster than ==, because it does not convert the different types. In addition, if you want to check a particular type ==== will do exactly what you requested, while == will convert the data only for a limited time and will try to use both types of operators.

PHP interview question #19

What do you know about our industry?

This question is very important, and some candidates will be unable to answer it. A PHP developer who knows, even vaguely, the industry in which you’re doing business, shows a certain curiosity and that he is able to take a step back.

PHP interview question #20

What is the correct way to create a function in PHP?

The answer to this very easy interview question is:

function functionName() {

  // Function code.

}

A candidate who is unable to answer it does not have sufficient PHP skills

PHP Interview Question #21

How to combine two strings in PHP?

To concatenate two string variables, just use the dot(.) operator

This results in a single string.

PHP Interview Question #22

How to connect a MySQL database using PHP?

MySQL is the most popular database system used with PHP. The answer to this interview question is to use mysql_connection function.

PHP interview question #23

What is the mail() function used for?

The answer to this question is that this function can be used to send an email from a PHP script.

PHP interview question #24

What type of corporate culture do you prefer?

Depending on whether your company has an entrepreneurial or managerial corporate culture, its operating mode is not the same. You should favor candidates who prefer the type of corporate culture in place in your organization.

However, it is preferable for the candidate to provide a nuanced answer. Indeed, a candidate who totally rejects a structured corporate culture may suggest that he or she will have difficulty following the guidelines. On the other hand, a candidate who answers that he/she hates entrepreneurial corporate culture may not be able to think outside the box, and to work independently. Don’t forget that soft skills are part of the skills a good PHP programmer should have.

Conclusion

We hope that these questions and their answers will be of great help when you will test a candidate PHP skills. If you are looking for additional interview questions, you can check out notions such as string, form, session, print and echo functions, variables or cookies. You can also find out more about interviewing a back-end developer at this url : https://www.codingame.com/work/how-to-hire-a-backend-developer/.  However, keep in mind that searching the web for questions about PHP is not the best way to know a candidate’s actual skills. Feel free to take a look at our evaluation tool, which offers the opportunity to evaluate developers’ PHP skills through technical coding tests, which are much more efficient than oral interview questions to hire a highly-qualified back-end programmer.