50 Most Common PHP Interview Questions

50 Most Common PHP Interview Questions

The demand for PHP jobs is increasing day by day. People who are searching or preparing for PHP jobs, have to face some common questions in the interview. So, if you are a fresher and want to make your career as PHP developer then you must read this article to increase your chance to get PHP job easily and fast. Most common PHP interview questions are discussed in this article with answers.

Q#01.  What is PHP?

PHP is one of the popular server-side scripting languages for developing the web application. The full form of PHP is Hypertext Preprocessor. It is used by embedding HTML to create dynamic content, communicate with a database server, handling session etc.

Q#02. Why do we use PHP?

There are many benefits of using PHP. First of all, it is totally free to use. So anyone can use PHP without any cost and host the site with minimal cost. It supports multiple databases. Most commonly used database is MySQL which is also free to use. Many PHP frameworks are used now for web development, such as CodeIgniter, CakePHP, Laravel etc. These frameworks make the web development task easier than before.

Q#03.  Is PHP a strongly typed language?

No. PHP is a weakly typed or loosely typed language. That means PHP does not require to declare data types of the variable when you declare any variable like other standard programming languages C# or Java. When you store any string value in a variable then the data type is the string and if you store the numeric value in that same variable then data type is Integer.

Sample code:

$var = "Hello";   //String

$var = 10; //Integer

Q#04.  What is mean by variable variables in PHP?

When the value of a variable is used as the name of other variables then it is called variable variables. $$ is used to declare variable variables in PHP.

Sample code:

$str = "PHP";

$$str = " Programming"; //declaring variable variables

echo "$str ${$str}<br/>"; //It will print "PHP programming"

echo "$PHP"; //It will print "Programming"

Q#05.  What are the differences between echo and print?

Both echo and print method prints the output in the browser but there is a difference between these two methods. echo does not return any value after printing the output and it works faster than print method. print method is slower than echo because it returns boolean value after printing the output.

Sample code:

echo "PHP Developer<br/>";

$n = print "Java Developer<br/>";

Q#06.  How can you execute PHP script from command line?

You have to use php command in command line to execute PHP script. If the PHP file name is test.php then the following command is used to run the script from command line.

phptest.php

Q#07.  How can you declare the array in PHP?

You can declare three types of arrays in PHP. These are numeric, associative and multidimensional arrays.

Sample code:

//Numeric Array

$computer = array("Dell", "Lenavo", "HP");

//Associative Array

$color = array("Sithi"=>"Red", "Amit"=>"Blue", "Mahek"=>"Green");

//Multidimensional Array

$courses = array ( array("PHP",50), array("JQuery",15), array("AngularJS",20) );

Q#08. What are the uses of explode() and implode() functions?

explode() function is used to split a string into an array and implode() function is used to make string by combining array elements.

Sample code:

$text = "I like programming";

print_r (explode(" ",$text));

$strarr = array('Pen','Pencil','Eraser');

echo implode(" ",$strarr);

Q#09. Which function can be used to exit from the script after displaying the error message?

You can use exit() or die() function to exit from the current script after displaying the error message.

Sample code:

if(!fopen('t.txt','r'))

exit("<br/>Unable to open the file");

Sample code:

if(!mysqli_connect('localhost','user','password'))

die("<br/>Unable to connect with the database");

Q#10. Which function is used in PHP to check the data type of any variable?

gettype() function is used to check the data type of any variable.

Sample code:

echogettype(true).'<br>'; //boolean

echogettype(10).'<br>'; //integer

echogettype('Web Programming').'<br>'; //string

echogettype(null).'<br>'; //NULL

Q#11. How can you increase the maximum execution time of script in PHP?

You will require to change the value of the max_execution_timedirective in php.ini file for increasing maximum execution time. For example, if you want to set the max execution time for 120 seconds then set the value as follows,

max_execution_time = 120

Q#12. What are mean by passing the variable by value and reference in PHP?

When the variable is passed as value then it is called pass variable by value. Here, the main variable remains unchanged when the passed variable changes.

Sample code:

functiontest($n) {

    $n=$n+10;

}

$m=5;

test($m);

echo $m;

When the variable is passed as the reference then it is called pass variable by reference. Here, both the main variable and passed variable share the same memory location and &is used for reference. So, if one variable changes then other will change. 

Sample code:

function test(&$n) {

    $n=$n+10;

}

$m=5;

test($m);

echo $m;

Q#13. What are type casting and type juggling?

The way by which PHP can assign a particular data type for any variable is called type casting. The required type of variable is mentioned in the parenthesis before the variable.

Sample code:

$str = "10";   // $str is now string

$bool = (boolean) $str;   // $bool is now boolean

PHP does not support data type for variable declaration. The type of the variable is changed automatically based on the assigned value and it is called type juggling.

Sample code:

$val = 5; // $val is now number

$val = "500"  //$val is now string

Q#14.  How can you make connection with MySQL server using PHP?

You have to provide MySQL hostname, username and password to make the connection with MySQL server in mysqli_connect() method or declaring database object of mysqli class.

Sample code:

$mysqli = mysqli_connect("localhost","username","password");

$mysqli = new mysqli("localhost","username","password");

Q#15. How can you retrieve data from MySQL database using PHP?

Many functions are available in PHP to retrieve data from MySQL database. These are mentioned below.

mysqli_fetch_array() – It is used to fetch records as a numeric array or an associative array.

Sample code:

// Associative or Numeric array

$result=mysqli_query($DBconnection,$query);

$row=mysqli_fetch_array($result,MYSQLI_ASSOC);

echo "Name is $row[0] <br/>";

echo "Email is $row['email'] <br/>";

mysqli_fetch_row() – It is used to fetch records as a numeric array.

Sample code:

//Numeric array

$result=mysqli_query($DBconnection,$query);

$row=mysqli_fetch_array($result);

printf ("%s %s\n",$row[0],$row[1]);

mysqli_fetch_assoc() – It is used to fetch records as an associative array.

Sample code:

// Associative array

$result=mysqli_query($DBconnection,$query);

$row=mysqli_fetch_array($result);

printf ("%s %s\n",$row["name"],$row["email"]);

mysqli_fetch_object() – It is used to fetch records as an object.

Sample code:

// Object

$result=mysqli_query($DBconnection,$query);

$row=mysqli_fetch_array($result);

printf ("%s %s\n",$row->name,$row->email);

Q#16. What are the differences between mysqli_connect and mysqli_pconnect?

mysqli_pconnect() function is used for making persistence connection with the database that does not terminate when the script ends. mysqli_connect() function searches any existing persistence connection first if no persistence connection exists then it will create a new database connection and terminate the connection at the end of the script.   

Sample code:

$DBconnection = mysqli_connect("localhost","username","password","dbname");

// Check for valid connection
if (mysqli_connect_errno())
{
            echo "Unable to connect with MySQL: " . mysqli_connect_error();
}

mysqli_pconnect() function is deprecated in the new version of PHP, but you can create persistence connection using mysqli_connect with the prefix p.

Q#17. Which function is used in PHP to count the total number of rows returned by any query?

mysqli_num_rows() function is used to count the total number of rows returned by the query.

Sample code:

$mysqli = mysqli_connect("hostname","username","password","DBname");

$result=mysqli_query($mysqli,"select * from employees");

$count=mysqli_num_rows($result);

Q#18. How can you create session in PHP?

session_start() function is used in PHP to create session.

Sample code:

session_start(); //Start session

$_SESSION['USERNAME']='Fahmida'; //Set a session value

unset($_SESSION['USERNAME']; //delete session value

Q#19. What is the use of imagetypes() method?

imagetypes() function returns the list of supported images of the installed PHP version. You can use this function to check particular image extension is supported by PHP or not.

Sample code:

//Check BMP extension is supported by PHP or not

if (imagetypes() & IMG_BMP) {
    echo "BMP extension Support is enabled";
}

Q#20. Which function you can use in PHP to open a file for reading or writing or for both?

You can use fopen() function to read or write or both in PHP.

Sample code:

$file1 = fopen("myfile1.txt","r"); //Open for reading

$file2 = fopen("myfile2.txt","w"); //Open for writing

$file3 = fopen("myfile3.txt","r+"); //Open for reading and writing

Q#21. What is the difference between include() and require()?

Both include() and require() function are used for including PHP script from a file to another file. But there is a difference between these functions. If any error occurs at the time of including a file using include() function then it continues the execution of the script after showing the error message. require() function stops the execution of the script by displaying the error message if an error occurs.

Sample code:

if (!include(‘test.php’)) echo “Error in file inclusion”;

if (!require(‘test.php’)) echo “Error in file inclusion”;

Q#22. Which function is used in PHP to delete a file?

unlink() function is used in PHP to delete any file.

Sample code:

unlink('filename');

Q#23. What is the use of strip_tags() method?

strip_tags() function is used to retrieve string from a text by omitting HTML, XML and PHP tags. This function has one mandatory parameter and one optional parameter. The optional parameter is used to accept particular tags.

Sample code:

//Remove all tags from the text

echo strip_tags("<b>PHP</b> is a popular <em>scripting</em> language");

//Remove all tags excluding <b> tag

echo strip_tags("<b>PHP</b> is a popular <em>scripting</em> language","<b>");

Q#24. How can you send HTTP header to the client in PHP?

header() function is used to send raw HTTP header to a client before any output is sent.

Sample code:

header('Location: http://www.your_domain/');

Q#25. Which functions are used to count the total number of array elements in PHP?

count() and sizeof() functions can be used to count the total number of array elements in PHP.

Sample code:

$names=array(“Asa”,”Prinka”,”Abhijeet”);
echo count($names);

$marks=array(95,70,87);
echo sizeof($marks);

Q#26. What is the difference between substr() and strstr()?

substr() function returns a part of the string based on the starting point and length. Length parameter is optional for this function and if it is omitted then the remaining part of the string from the starting point will be returned. 

strstr() function searches the first occurrence of is string inside another string. The third parameter of this function is optional and used to retrieve the part of the string that appears before the first occurrence of the searching string.

Sample code:

echosubstr("Computer Programming",9,7); //Returns “Program”

echo substr("Computer Programming",9); //Returns “Programming”

Sample code:

echo strstr("Learning Laravel 5!","Laravel"); //Returns Laravel 5!

echo strstr("Learning Laravel 5!","Laravel",true); //Returns Learning

Q#27. How can you upload a file using PHP?

To upload a file by using PHP, you have to do the following tasks.

1.      Enable file_uploads directive

Open php.ini file and find out file_uploads directive and make it on.

file_uploads = On

2.      Create an HTML form using enctype attribute and file element for uploading the file.

<form action="upload.php" method="post" enctype="multipart/form-data">

<input type="file" name="upd" id="upd">

<input type="submit" value="Upload" name="upload">

</form>

3.      Write PHP script to upload the file

if (move_uploaded_file($_FILES["upd"]["tmp_name"], "Uploads/")) {

echo "The file ". basename( $_FILES["upd"]["name"]). " is uploaded.";

} else {

echo "There is an error in uploading.";

}

Q#28. How can you declare the constant variable in PHP?

define() function is used to declare constant variable in PHP. Constant variable declares without $ symbol.

Sample code:

define("PI",3.14);  

Q#29. Which function is used in PHP to search a particular value in an array?

in_array() function is used to search a particular value in an array.

Sample code:

$languages = array("C#", "Java", "PHP", "VB.Net");

if (in_array("PHP", $languages))   {

  echo "PHP is in the list";

 }

else   {

  echo "php is not in the list";

 }

Q#30. What is the use of $_REQUEST variable?

$_REQUEST variable is used to read data from the submitted HTML form.

Sample code:

Here, $_REQUEST variable is used to read the submitted form field with the name ‘username’. If the form will submit without any value then it will print “Name is empty”, otherwise it will print the submitted value.

<?php

if (isset($_POST['submit'])) {

    // collect value of input field

    $name = $_REQUEST['username'];

    if (empty($name)) {

        echo "Name is empty";

    } else {

        echo $name;

    }

}

else

{

?>

<form method="post" action="#">

  Name: <input type="text" name="username">

<input type="submit" name="submit">

</form>

<?php }  ?>

Q#31. What is the difference between for and foreach loop in PHP?

for loop is mainly used for iterating pre-defined number of times and foreach loop is used for reading array elements or mysql resultset where the number of iteration can be unknown.

Sample code:

//Loop will iterate for 5 times

for ($n = 0; $n <= 5; $n++) {
    echo "The number is: $n <br>";
} 

Sample code:

//Loop will iterate based on array elements

$parts = array("HDD", "Monitor", "Mouse", "Keyboard"); 

foreach ($parts as $value) {
    echo "$value <br>";
}

Q#32. How long does a PHP session last for?

By default, session data last for 24 minutes or 1440 seconds in PHP. But if you want you can change the duration by modifying the value of gc_maxlifetime directive in php.ini file. To set the session time for 30 minutes, open php.ini file and set the value of gc_maxlifetime directive as follows,

gc_maxlifetime = 1800

Q#33. What is the difference between “= =” and “= = =” operators.

“= =” is called equivalent operator that is used to check only the equivalency of two values butnot the data types.

Sample code:

10 and “10” are equivalent by values. So the if condition will be true and print “n is equal to 10”.

$n = 10;

if ($n == "10")

            echo "n is equal to 10"; //This will print

else

            echo "n is not equal to 10";

“= = =” is called strictly equivalent operator that is used to check the equivalency of two values by comparing both data types and values.

Sample code:

10 and “10” are equal by values but not equal by data type. One is string and one is number. So, if condition will be false and print “n is not equal to 10”.

$n = 10;

if ($n === "10")

            echo "n is equal to 10";

else

            echo "n is not equal to 10"; //This will print

Q#34. Whichoperator is used to combine string values in PHP?

Two or more string values can be combined by using ‘.’ operator.

Sample code:

$val1 = "Software ";

$val2 = "Testing";

echo $val1.$val2; // The output is “Software Testing”

Q#35. What is PEAR?

The full form of PEAR “PHP Extension and Application Repository”. Anyone can download reusable PHP components by using this framework freely. It contains different types of packages from different developers.

The URL address of PEAR is,

https://pear.php.net

Q#36. What type of errors can be occurred in PHP?

Different types of errors can occur in PHP. Some major error types are mentioned here.

Fatal Errors– The execution of the script stops when this error occurs.

Sample code:

In the following script, f1() function is declared but f2() function is called which is not declared.  The execution of the script will stop when f2() function will call. So, “Testing Fatal Error” will not be printed.

function f1(){

            echo "function 1";

}

f2();

echo “Testing Fatal Error”;

Parse Errors- This type of error occurs when the coder uses wrong syntax in the script.

Sample code:

Here, semicolon(;) is missing at the end of the first echo statement.

echo "This is a testing script<br/>"

echo "error";

Warning Errors- This type of error does not stop the execution of the script. It continues the script after displaying the error.

Sample code:

In the following script, if test.txt file does not exist in the current location then a warning message will display to show the error and print “Opening File” text by continuing the execution.

$handler = fopen("test.txt","r");

echo "Opening File";

Notice Errors- This type of error shows the minor error of the script and continues the execution after displaying the error.

Here, the variable, $a is defined but $b is not defined. So, a notice of undefined variable will display for “echo $b” statement and print “Checking notice error” by continuing the script.

Sample code:

$a = 100;

echo $b;

echo "Checking notice error";

Q#37. Does PHP support multiple inheritances?

PHP does not support multiple inheritances. To implement the features of multiple inheritances, the interface is used in PHP.

Sample code:

Here, two interfaces, Isbn and Type are declared and implemented in a class, book Details to add the feature of multiple inheritances in PHP.

interface Isbn {

  public function setISBN($isbn);

  }

interface  Type{

  public function setType($type);

 }

class bookDetails implements Isbn, Type {

  private $isbn;

  private $type;

  public function setISBN($isbn)

  {

    $this -> isbn = $isbn;

  }

  public function setType($type)

  {

    $this -> type = $type;

  }

  }

Q#38. What are the differences between session and cookie?

The session is a global variable which is used in the server to store the session data. When a new session creates the cookie with the session id is stored in the visitor's computer. Session variable can store more data than cookie variable. Session data are stored in $_SESSION array and Cookie data are stored in $_COOKIE array. Session values are removed automatically when the visitor closes the browser and cookie values are not removed automatically.

Q#39. What is the use of mysqli_real_escape_string() function?

mysqli_real_escape_string() function is used to escape special characters from the string for using SQL statement.

Sample code:

$DBconnection=mysqli_connect("localhost","username","password","dbname");

$productName = mysqli_real_escape_string($con, $_POST['proname']);

$ProductType = mysqli_real_escape_string($con, $_POST['protype']);

Q#40. Which functions are used to remove whitespaces from the string?

There are three functions in PHP to remove whitespaces from the string.

trim() – it removes whitespaces from the left and right side of the string.

ltrim() – it removes whitespaces from the from the left side of the string.

rtrim() – it removes whitespaces from the from the right side of the string.

Sample code:

$str = "     Tutorials for your help    ";

$val1 = trim($str);

$val2 = ltrim($str);

$val3 = rtrim($str);

41. What is persistence cookie?

The cookie file that is stored permanently in the browser is called persistence cookie. It is not secure and used for tracking visitor for long times. This type of cookie can be declared as follows,

setccookie ("cookie_name", "cookie_value", strtotime("+2 years");

42. How does the cross-site scripting attack can be prevented by PHP?

Htmlentities() function of PHP can be used for preventing cross-site scripting attack.

43. Which PHP global variable is used for uploading a file?

$_FILE[] array contains all information of the uploaded file. The use of various indexes of this array is mentioned below.

$_FILES[$fieldName]['name'] – Keeps the original file name.
$_FILES[$fieldName]['type'] – Keeps the file type of the uploaded file.
$_FILES[$fieldName]['size'] – Stores the file size in bytes.
$_FILES[$fieldName]['tmp_name'] – Keeps the temporary file name which is used to store the file in the server.
$_FILES[$fieldName]['error'] – Contains error code related to the error thatappears during the upload.

44. What are mean by public, private, protected, static and final scopes?

Ø  Public- variables, classes and methods which are declared public can be accessed from anywhere.

Ø  Private-   variables, classes and methods which are declared private can access by the parent class only.

Ø  Protected- variables, classes, and methods which are declared protected can be access by the parent and child classes only.

Ø  Static- The variable which is declared static can keep the value after losing the scope.

Ø  Final- This scope prevents child class to declare the same item again.

45.How image properties can be retrieved in PHP?

getimagesize()-it is used to get the image size.

exif_imagetype()-it is used to get the image type.

imagesx()-it is used to get the image width.

imagesy()-it is used to get the image height.

46.What is the difference between abstract class and interface?

Ø  Abstract classes are used for closely related objects and interfaces are used for unrelated objects.

Ø  PHP class can implement multiple interfaces but can’t inherit multiple abstract classes.

Ø  Common behavior can be implemented in the abstract class but not an interface.

47. What is garbage collection?

It is an automated feature of PHP. When it runs, it removes all sessions data which are not accessed for long times. It runs on /tmp directory which is the default session directory. PHP directives which are used for garbage collection are,

Ø  session.gc_maxlifetime (default value, 1440)

Ø  session.gc_probability (default value, 1)

Ø  session.gc_divisor (default value, 100)

48. Which library is used in PHP to do various types of Image work?

Using GD library various types of image work can be done in PHP, such as rotating image, cropping an image, creating image thumbnail etc.

49. What is URL rewriting?

Appending the session ID in every local URL of the requested page for keeping session information is called URL rewriting. The disadvantages of this methods are, it doesn't allow persistence between the sessions and, the user can easily copy and paste the URL and send to another user.

50. What is PDO?

The full form of PDO is PHP Data Objects. It is a lightweight PHP extension that uses consistence interface for accessing the database. Using PDO, the developer can easily switch from one database server to other. But it does not support all advanced features of the new MySQL server.

Hope, this article will increase your confidence level to face PHP interview. Thank you.

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