PHP Interview Questions and Answers for Web Developers - Part 1

In this article on PHP Interview Questions, I have compiled a list of very basic and fundamental PHP interview questions and answers for web developers. Every PHP web developer should know these basic questions of PHP. So, if you are preparing for any interview in PHP development, you should go through the following list of PHP basic interview questions. There PHP questions are based on very simple PHP concepts like basic introduction to PHP, Sessions and Cookies in PHP, Input / Output in PHP, Error Management in PHP, MySQL database connectivity in PHP, SQL Injection in PHP, Encryption and Decryption in PHP, Sending Emails in PHP, datatypes in PHP and many more. Lets have a look...

1. What is PHP?

PHP is a server side scripting object oriented language commonly used for web applications. 

2. What is the use of "echo" in php?

It is used to print a data in the webpage.


<?php echo 'Hi'; ?>

The above code print the text in the webpage

3. How to include a file to a php page?

We can include a file using "include()" or "require()" function with file path as its parameter.

4. What's the difference between include and require?

If the file is not found by require(), it will cause a fatal error and halt the execution of the script. If the file is not found by include(), a warning will be issued, but execution will continue.

5. What is difference between require_once(), require() and include()?

require() includes and evaluates a specific file, while require_once() does that only if it has not been included before (on the same page). So, require_once() is recommended to use when you want to include a file where you have a lot of functions for example. This way you make sure you don't include the file more times and you will not get the "function re-declared" error.

6. Differences between GET and POST methods?

We can send 1024 bytes using GET method but POST method can transfer large amount of data and POST is the secure method than GET method .

7. How to declare an array in php?

Eg : var $arr = array('apple', 'grape', 'lemon');

8. What is the use of 'print' in php?

This is not actually a real function, It is a language construct. So you can use without parentheses with its argument list.


print('PHP Interview Questions'); 
print 'PHP Interview Questions';

9. What is use of in_array() function in php?

in_array used to checks if a value exists in an array

10. What is use of count() function in php?

count() is used to count all elements in an array, or something in an object

11. What is the difference between Session and Cookie?

The main difference between sessions and cookies is that sessions are stored on the server, and cookies are stored on the user’s computers in the text file format. Cookies can not hold multiple variables, but Session can hold multiple variables. We can set expiry for a cookie while the session only remains active as long as the browser is open. Users do not have access to the data you stored in Session because it is stored in the server. Session is mainly used for login/logout purpose while cookies using for user activity tracking

12. How to set cookies in PHP?

Setcookie("sample", "ram", time()+3600);

13. How to retrieve a Cookie Value?

eg : echo $_COOKIE["user"];

14. How to create a session? How to set a value in session ? How to remove data from a session?

Create session : session_start();
Set value into session : $_SESSION['USER_ID']=1;
Remove data from a session : unset($_SESSION['USER_ID'];

15. What types of loops exist in php?

for,while,do while and foreach 

16. How to create a mysql connection?


17. How to select a database?


18. How to execute an sql query? How to fetch its result ?

$my_qry = mysql_query("SELECT * FROM `users` WHERE `u_id`='1'; "); 
$result = mysql_fetch_array($my_qry);
echo $result['First_name'];

19. Write a program using while loop

$my_qry = mysql_query("SELECT * FROM `users` WHERE `u_id`='1'; "); 
while($result = mysql_fetch_array($my_qry))
   echo $result['First_name'.]."<br/>";

20. How we can retrieve the data in the result set of MySQL using PHP?

1. mysql_fetch_row
2. mysql_fetch_array
3. mysql_fetch_object
4. mysql_fetch_assoc

21. What is the use of explode() function?

Syntax : array explode ( string $delimiter , string $string [, int $limit ] ); 

This function breaks a string into an array. Each of the array elements is a substring of string formed by splitting it on boundaries formed by the string delimiter.

22. What is the difference between explode() and split() functions?

Split function splits string into array by regular expression. Explode splits a string into array by string.

23. What is the use of mysql_real_escape_string() function?

It is used to escapes special characters in a string for use in an SQL statement

24. Write down the code for save an uploaded file in php.

if ($_FILES["file"]["error"] == 0)
      "upload/" . $_FILES["file"]["name"]);
      echo "Stored in: " . "upload/" . $_FILES["file"]["name"]; 

25. How to create a text file in php?

$filename = "/home/user/guest/newfile.txt";
$file = fopen( $filename, "w" );
if( $file == false )
echo ( "Error in opening new file" ); exit();
fwrite( $file, "This is a simple test\n" );
fclose( $file );

26. How to strip whitespace (or other characters) from the beginning and end of a string?

The trim() function removes whitespaces or other predefined characters from both sides of a string.

27. What is the use of header() function in php?

The header() function sends a raw HTTP header to a client browser.Remember that this function must be called before sending the actual out put.For example, You do not print any HTML element before using this function.

28. How to redirect a page in php?

The following code can be used for it, header("Location:index.php");

29. How stop the execution of a php script?

exit() function is used to stop the execution of a page

30. How to set a page as a home page in a php based site?

index.php is the default name of the home page in php based sites

31. How to find the length of a string?

strlen() function used to find the length of a string

32. What is the use of rand() in php?

It is used to generate random numbers.If called without the arguments it returns a pseudo-random integer between 0 and getrandmax(). If you want a random number between 6 and 12 (inclusive), for example, use rand(6, 12).This function does not generate cryptographically safe values, and should not be used for cryptographic uses. If you want a cryptographically secure value, consider using openssl_random_pseudo_bytes() instead.

33. What is the use of isset() in php?

This function is used to determine if a variable is set and is not NULL

34. What is the difference between mysql_fetch_array() and mysql_fetch_assoc()?

mysql_fetch_assoc function Fetch a result row as an associative array, While mysql_fetch_array() fetches an associative array, a numeric array, or both

35. What is mean by an associative array?

Associative arrays are arrays that use string keys is called associative arrays.

36. What is the importance of "method" attribute in a html form?

"method" attribute determines how to send the form-data into the server.There are two methods, get and post. The default method is get.This sends the form information by appending it on the URL.Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.

37. What is the importance of "action" attribute in a html form?

The action attribute determines where to send the form-data in the form submission.

38. What is the use of "enctype" attribute in a html form?

The enctype attribute determines how the form-data should be encoded when submitting it to the server. We need to set enctype as "multipart/form-data" when we are using a form for uploading files

39. How to create an array of a group of items inside an HTML form?

We can create input fields with same name for "name" attribute with squire bracket at the end of the name of the name attribute, It passes data as an array to PHP. 

For instance :

<input name="MyArray[]" />  <input name="MyArray[]" />  <input name="MyArray[]" />  <input name="MyArray[]" />

40. Define Object-Oriented Methodology.

Object orientation is a software/Web development methodology that is based on the modeling a real world system.An object is the core concept involved in the object orientation. An object is the copy of the real world enity.An object oriented model is a collection of objects and its inter-relationships

41. How do you define a constant?

Using define() directive, like define ("MYCONSTANT",150)

42. How send email using php?

To send email using PHP, you use the mail() function.This mail() function accepts 5 parameters as follows (the last 2 are optional). You need webserver, you can't send email from localhost. eg : mail($to,$subject,$message,$headers);

43. How to find current date and time?

The date() function provides you with a means of retrieving the current date and time, applying the format integer parameters indicated in your script to the timestamp provided or the current local time if no timestamp is given. In simplified terms, passing a time parameter is optional - if you don't, the current timestamp will be used.

44. Difference between mysql_connect and mysql_pconnect?

There is a good page in the php manual on the subject, in short mysql_pconnect() makes a persistent connection to the database which means a SQL link that do not close when the execution of your script ends. mysql_connect()provides only for the databasenewconnection while using mysql_pconnect , the function would first try to find a (persistent) link that's already open with the same host, username and password. If one is found, an identifier for it will be returned instead of opening a new connection... the connection to the SQL server will not be closed when the execution of the script ends. Instead, the link will remain open for future use.

45. What is the use of "ksort" in php?

It is used for sort an array by key in reverse order.

46. What is the difference between $var and $$var?

They are both variables. But $var is a variable with a fixed name. $$var is a variable who's name is stored in $var. For example, if $var contains "message", $$var is the same as $message.

47. What are the encryption techniques in PHP?

MD5: PHP implements the MD5 hash algorithm using the md5 function.

eg : $encrypted_text = md5 ($msg);

mcrypt_encrypt: string mcrypt_encrypt ( string $cipher , string $key , string $data , string $mode [, string $iv ] ); 

Encrypts plaintext with given parameters

48. What is the use of the function htmlentities?

htmlentities Convert all applicable characters to HTML entities This function is identical to htmlspecialchars() in all ways, except with htmlentities(), all characters which have HTML character entity equivalents are translated into these entities.

49. How to delete a file from the system?

Unlink() deletes the given file from the file system.

50. How to get the value of current session id?

session_id() function returns the session id for the current session.

51. What are the differences between mysql_fetch_array(), mysql_fetch_object(), mysql_fetch_row()?

Mysql_fetch_array Fetch a result row as an associative array, a numeric array, or both.
mysql_fetch_object ( resource result ) Returns an object with properties that correspond to the fetched row and moves the internal data pointer ahead. Returns an object with properties that correspond to the fetched row, or FALSE if there are no more rows
mysql_fetch_row() fetches one row of data from the result associated with the specified result identifier. The row is returned as an array. Each result column is stored in an array offset, starting at offset 0.

52. What are the different types of errors in PHP?

Here are three basic types of runtime errors in PHP:

1. Notices: These are trivial, non-critical errors that PHP encounters while executing a script - for example, accessing a variable that has not yet been defined. By default, such errors are not displayed to the user at all - although you can change this default behavior.

2. Warnings: These are more serious errors - for example, attempting to include() a file which does not exist. By default, these errors are displayed to the user, but they do not result in script termination.

3. Fatal errors: These are critical errors - for example, instantiating an object of a non-existent class, or calling a non-existent function. These errors cause the immediate termination of the script, and PHP's default behavior is to display them to the user when they take place.

53. What is SQL Injection?

SQL injection is a malicious code injection technique.It exploiting SQL vulnerabilities in Web applications

54. What is x+ mode in fopen() used for?

Read/Write. Creates a new file. Returns FALSE and an error if file already exists

55. How to find the position of the first occurrence of a substring in a string?

strpos() is used to find the position of the first occurrence of a substring in a string

56. What is PEAR?

PEAR is a framework and distribution system for reusable PHP components.The project seeks to provide a structured library of code, maintain a system for distributing code and for managing code packages, and promote a standard coding style.PEAR is broken into three classes: PEAR Core Components, PEAR Packages, and PECL Packages. The Core Components include the base classes of PEAR and PEAR_Error, along with database, HTTP, logging, and e-mailing functions. The PEAR Packages include functionality providing for authentication, networking, and file system features, as well as tools for working with XML and HTML templates.

57. Distinguish between urlencode and urldecode?

This method is best when encode a string to used in a query part of a url. it returns a string in which all non-alphanumeric characters except -_. have replece with a percentege(%) sign . the urldecode->Decodes url to encode string as any %and other symbole are decode by the use of the urldecode() function.

I will come up with more PHP interview questions and answers in second part of this post.

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