Compilation of Commonly Asked PHP Interview Questions

PHP Developer Interview Questions

Before participating in any interview, it’s crucial to thoroughly prepare your professional knowledge, review your experiences, and delve deep into the company and the interview position to present yourself with the most confidence. PHP interviews are no exception and below are some PHP interview questions you may encounter. Let’s go through it with SmartOSC Careers!

1. Questions about Yourself

Before getting into technical PHP interview questions, let’s go through some basic self-introduction questions that recruiters commonly ask. Although these questions are familiar, it is essential to prepare for answering them smoothly and confidently.

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Question 1: Can you briefly introduce yourself?

This is a common question that you will be asked during a job interview. You can totally prepare and practice it in advance at home. The answer should be concise, around 2-3 minutes. Additionally, it is essential to provide all the necessary information for the employer, especially regarding your experience related to the PHP position.

Question 2: What are your strengths and weaknesses?

This is the section where you will assess your strengths and weaknesses. Based on this, the employer will have the most comprehensive view of your personality and character. They can also determine whether you are suitable for the position they are hiring for, as well as fitting into the company culture or not.

Question 3: What do you know about our company?

Recruiters are very interested in how well you know about their company. Most importantly, they want to know if the candidate truly understands the company and has done research before participating in the interview. Therefore, you should thoroughly research the company and address relevant issues such as its field of activity, culture, and how its operations are structured.

PHP Interview Questions

2. PHP Interview Questions

Question 1: How many ways to declare PHP? What are the official ways that do not affect future updates?

There are 4 tags to declare PHP. However, there are only two ways that are considered official and approved worldwide:

  • <?php…?> → It’s the official way.
  • <script language=”PHP”>…</script> → It is also considered an official tag that does not affect updates to future PHP versions.
  • <?…?> → (“Must enable it from settings to use” It is not necessary to say.)
  • <%…%> → (“Must enable it from settings to use” It is not necessary to say.)

Question 2: What is the difference between a variable and a constant? If a constant is defined twice, what happens?

  • Variables can change, but constants cannot. 
  • A constant is essentially a type of variable but with an unchangeable value. Even if defined twice, a constant maintains its originally declared value.
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Syntax: define(‘Constant name’, value);

Question 3: Differentiate between $_POST and $_GET in PHP.

Both $_GET and $_POST are used to send data to the server.

  • $_GET: Send data to the server via URL, so data information is displayed on the URL. As a result, security is poor, data sent is limited to 1024 characters.
  • $_POST: Sends data to the server in hidden form via HTTP Header so it has higher security than GET, data sent is not limited.
  • However, Post’s processing speed is slower than Get’s.

Question 4: What is the difference between Session and Cookie?

Cookie Session
Cookie data is stored on the client side. Session data is stored on the server side.
Cookie data is easy to modify or steal when it is stored on the client side. Session data are not easily modified because they are stored on the server side.
Cookie data is available in the browser until expired. After closing the browser, the session will end.

Question 5: What is the difference between & operators and && operators in PHP?

The & and && operators in PHP are both AND operations, however, the & sign operator applies bitwise. It is easier to understand that an & sign is an AND operation that operates on bits, for example, 1 & 0 produces 0. The double & sign operation only applies to boolean types True and False.

Question 6: How are $a++ and ++$a different?

Both are used to increment a given variable by one. However, the difference is that $a++ runs after it is called, while ++$a runs immediately when it is called. Taking the example of $a being 5, when using the echo function to print it with the value of $a++, it will display as 5. On the other hand, when using echo for ++a, the displayed value will be 6.


Question 7: What is an array? How many types of arrays are there in PHP?

An array is a variable that can hold many elements, from which we can easily store, arrange, or delete elements in the array.

The array includes two components: KEY and VALUE. The key is used to access the elements of the array. From that, we can assign values or get values of the elements in the array.

Arrays have 3 main types:

  • Indexed arrays – Arrays with a numeric index
  • Associative arrays – Arrays with named keys
  • Multidimensional arrays – Arrays containing one or more arrays

Question 8: What is an Indexed array? How is it different from an Associative array? Which loop is commonly used to traverse an array?

The keys of an indexed array are integers, beginning at 0. In an indexed array, the KEY is arranged ascending from 0. Meanwhile, the key in the associative array is not arranged in any order. 

To browse arrays, we can use any loop. However, the most standard is to use a foreach loop, because this loop was built by PHP developers specifically for array browsing because it is easier to use and faster. Its processing is faster.

Question 9: Which function is used to convert an array to a string? To split a string into an array, which function is used?

PHP provides the implode function (separator, array) used to convert an array into a string and the explode function (separator, string,[limit]) used to convert a string into an array. In addition, we have the join function($ky_tu,$array) similar to the implode function

Question 10: In PHP, what function do we use to combine arrays? What function do we use to separate arrays?

PHP provides the array merge function($array1, $array2, $array3,…) used to join arrays into a single array and the array slice function(array,start,[length],[preserve]) used to split the array into a smaller array. 

Question 11: How is an abstract class different from an interface?

Abstract classes are used to provide a base class for concrete subclasses to inherit from, while interfaces are used to define a set of methods that a class must implement.

Abstract classes can have implemented and abstract methods, while interfaces can only have abstract methods.

Question 12: What is a trait, and what are its advantages?

Traits are a code reuse mechanism in single-inheritance languages like PHP. Traits are used to limit single inheritance by allowing sets of methods to be used freely in several independent classes in different class hierarchies.

Strengths of trait:

  • Avoid repeating code 
  • Prevent complex inheritance
  • Provides a simple way to reuse code, increasing program performance

Question 13. What is API?

  • API: Application Programming Interfaces are methods and protocols for connecting to other directories and applications.
  • The API provides access to a set of commonly used functions. And from there, it is possible to exchange application data

PHP Interview Questions

Above is a compilation of common PHP interview questions. We hope that the information we provide will help you prepare well for the position you are applying for. At the moment, SmartOSC is hiring for various IT positions, including the PHP Fresher position. Apply now at: 



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