1. Differentiate between variables and constants in PHP

2. What is a session in PHP?

When you work with an application, you open it, do some modifications, and then you close it. This is much like a Session. The computer knows who you are. It knows when the application is started and ended by you.

But on the internet, the webserver does not know who you are or what you do, because the HTTP address doesn’t maintain a state. This problem is solved using session variables by storing user information to be used across multiple pages (e.g. username, favorite color, etc).

By default, session variables will last until the user closes the browser.

So Session variables hold single user information and are available to all pages in one application.

3. What does PEAR stands for?

PEAR provides a higher level of programming for web developers. It contains all kinds of PHP code snippets and libraries. It also provides you with a command-line interface to automatically install packages.

4. Explain the difference between $message and $$message.

5. Is PHP a case-sensitive language?

For example, user-defined functions in PHP can be defined in lowercase but later referred to in uppercase, and it would still Function normally.

6. What are the different types of variables present in 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();

7. What are the rules for naming a PHP variable?

• A variable must start with a dollar symbol, followed by the variable name. For example: $price=100; where price is a variable name.
• Variable names must begin with a letter or underscore.
• A variable name can consist of letters, numbers, or underscores. But you cannot use characters like + , – , % , & etc.
• A PHP variable name cannot contain spaces.
• PHP variables are case-sensitive. So $NAME and $name both are treated as different variables.

8. What is the difference between “echo” and “print” in PHP?

9. Tell me some of the disadvantages of PHP

• PHP is not suitable for giant content-based web applications.
• Since it is open-source, it is not secure. Because ASCII text files are easily available.
• Change or modification in the core behavior of online applications is not allowed by PHP.
• If we use more features of the PHP framework and tools, it will cause poor performance of online applications.
• PHP features a poor quality of handling errors. PHP lacks debugging tools, which are needed to look for warnings and errors. It has only a few debugging tools in comparison to other programming languages.

10. How can PHP and HTML interact?

PHP is a server-side language whereas HTML is a client-side language. So PHP executes on the server-side and gets its results as strings, objects, arrays, and then we use them to display its values in HTML.

This interaction helps bridge the gaps and use the best of both languages.

11. What is the purpose of @ in PHP?

12. Explain the importance of Parser in PHP?

You can parse PHP code with PHP using the token_get_all() function.

13. What are the different types of Array in PHP?

Indexed Array

An array with a numeric key is known as the indexed array. Values are stored and accessed in linear order.

Associative Array

An array with strings for indexing elements is known as the associative array. Element values are stored in association with key values rather than in strict linear index order.

Multidimensional Array

An array containing one or more arrays within itself is known as a multidimensional array. The values are accessed using multiple indices.

14. Explain the main types of errors.

• Notices: Notices are non-critical errors that can occur during the execution of the script. These are not visible to users. Example: Accessing an undefined variable.
• Warnings: These are more critical than notices. Warnings don’t interrupt the script execution. By default, these are visible to the user. Example: include() a file that doesn’t exist.
• Fatal: This is the most critical error type which, when occurs, immediately terminates the execution of the script. Example: Accessing a property of a non-existent object or require() a non-existent file.

15. What are traits?

A trait is intended to reduce the limitations of single inheritance by enabling a developer to reuse sets of methods freely in many independent classes living in different hierarchies of class.

16. Does JavaScript interact with PHP?

17. How does the ‘foreach’ loop work in PHP?

The working of foreach is simple, with every single pass of the value, elements get assigned a value, and pointers are incremented. This process is repeatedly done until the end of the array has been reached.

The syntax for using the foreach statement in PHP is given below:

foreach($array as $value)
{
   Code inside the loop;
}

18. What is the most used method for hashing passwords in PHP?

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

This function is used to copy all the contents of a file called within the function, text wise into a file from which it is called.

When the file is included cannot be found, it will only produce a warning (E_WARNING) and the script will continue the execution.

require() function:

The require() function performs same as the include() function. It also takes the file that is required and copies the whole code into the file from where the require() function is called.

When the file is included cannot be found, it will produce a fatal error (E_COMPILE_ERROR) and terminates the script.

20. What are cookies? How to create cookies in PHP?

After verifying the user’s identity in encrypted form, cookies maintain the session id generated at the back end. It must reside in the browser of the machine. You can store only string values not object because you cannot access any object across the website or web apps.

By default, cookies are URL particular. For example, Gmail cookies are not supported by Yahoo and vice versa. Cookies are temporary and transitory by default. Per site 20 cookies can be created in a single website or web app. 50 bytes is the initial size of the cookie and 4096 bytes is the maximum size of the cookie.

In PHP, we can create cookies using the setcookie() function:

setcookie(name, value, expire, path, domain, secure, httponly);

Here name is mandatory and the remaining parameters are optional.

Example:
setcookie(“instrument_selected”, “guitar”)

21. What is the difference between ASP.NET and PHP?

22. What is the meaning of ‘escaping to PHP’?

For example, when you’re defining a string, you surround it in either double quotes or single quotes:
“Hello, InterviewPreparation.”

But what if I include double quotes within the string?
“Hello “InterviewPreparation.””

Now I have ambiguity – the interpreter doesn’t know where does my string end. If I want to keep my double quotes, I have various options. I could use single quotes around my string:
‘Hello “InterviewPreparation.”‘

Or I can escape my quotes:
“Hello \”InterviewPreparation.\””

Any quote that is preceded by a slash is escaped and understood to be part of the value of the string.

23. Explain Path Traversal

Path Traversal is also called “Directory Traversal”. It allows the attacker to exploit vulnerabilities present in the web file under attack.

Let’s take a simple example. Consider we have a “Show File” button that opens up some URL.

For a classic directory traversal attack, the attacker may try to access the system file /etc/passwd (assuming a UNIX/LINUX system). If the application receives the value of the file parameter from the URL and passes it to a system call, it would traverse the relative path ../../etc/passwd starting from /var/www and ask the system to load the password file.

This technique is also called a dot-dot-slash attack, because it usually uses the special characters ../ (or \.. on Windows) to climb to a higher-level directory.

24. What is the meaning of a final method and a final class?

This is especially useful when we are creating an immutable class like the String class. Only classes and methods may be declared final, properties cannot be declared as final.

25. What are the steps to create a new database using MySQL and PHP?

• A connection establishment is done to the MySQL server using the PHP script.
• The connection is validated. If the connection is successful, then you can write a sample query to verify.
• Queries that create the database are input and later stored into a string variable.
• Then, the created queries will be executed one after the other.

26. What is the use of session_start() and session_destroy() functions in PHP?

Syntax:

session_start();

The session_destroy() function is used to destroy all of the session variables as given below:

session_start();
session_destroy();
?>

27. What is Memcache and Memcached in PHP? Is it possible to share a single instance of a Memcache between several projects of PHP?

Memcache is a memory storage space. We can run Memcache on a single or several servers. Therefore, it is possible to share a single instance of Memcache between multiple projects.

It is possible to configure a client to speak to a separate set of instances. Therefore, it is allowed to run two different Memcache processes on the same host. Despite running on the same host, both of such Memcache processes stay independent, unless there is a partition of data.

28. What are the different ways of handling the result set of MySQL in PHP?

• mysqli_fetch_array(): Returns the current row of the result set as an associative array, a numeric array, or both.
• mysqli_fetch_assoc(): Returns the current row of the result set as an associative array.
• mysqli_fetch_object(): Returns the current row of a result set, as an object.
• mysqli_fetch_row(): Returns result row as an enumerated array.

29. How to connect to a URL in PHP?

The term cURL stands for client-side URL. cURL make use of libcurl(client-side URL Transfer Library) which supports many protocols like FTP, FTPS, HTTP/1, HTTP POST, HTTP PUT, HTTP proxy, HTTPS, IMAP, Kerberos etc. It allows you to connect to a URL and retrieve and display information from that page – like the HTML content of the page, HTTP headers, and their associated data, etc.

Steps for connecting with URL using PHP cURL POST are given below:

• Initialize cURL session.
• Define your URL where you want to post the request. We can directly enter this URL into the URL section inset option parameter or we can assign it to an object.
• Now, define the cURL options that you want to execute with the post option.
• After setting all the functions then it’s time to execute our cURL.
• After this, close the cURL and echo your object to check their response.

//Step 1 To initialize curl
     $ch = curl_init();
//Step 2 To set url where you want to post
     $url = ‘http://www.localhost.com’;
//Step 3 Set curl functions which are needs to you
     curl_setopt($ch,CURLOPT_URL,$url);
     curl_setopt($ch,CURLOPT_POST,true);
     curl_setopt($ch,CURLOPT_RETURNTRANSFER,true);
     curl_setopt($ch,CURLOPT_POSTFIELD,’postv1 = value1&postv2 = value2’);
//Step 4 To execute the curl
     $result = curl_exec($ch);
//Step 5 Close curl
     curl_close($ch);

30. How to create API in PHP?

Now, REST API is the web architecture that uses HTTP protocol for exchanging data between two functions that means your application or system. Now, let us have a look at how to create REST API in PHP by considering the example of accessing data from a database using PHP script.

Step 1 – Create a database: To create a database run the query given below:

CREATE DATABASE phptest;

Step 2 – Create a table: After creating a database, you have to create a table with dummy data. To create a table run the query given below:

CREATE TABLE IF NOT EXISTS `transactions` 
(
   `id` int(20) NOT NULL AUTO_INCREMENT,
   `order_id` int(50) NOT NULL,
   `amount` decimal(9,2) NOT NULL,
   `response_code` int(10) NOT NULL,
   `response_desc` varchar(50) NOT NULL,
   PRIMARY KEY (`id`),
   UNIQUE KEY `order_id` (`order_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 ;

Step 3 – Create a Database Connection: Create a db.php file and paste the below-given database connection in it. Make sure to update these credentials with your database credentials.

// Enter your Host, username, password, database below.
$con = mysqli_connect("localhost","root","","phptest");
if (mysqli_connect_errno())
{
    echo "Failed to connect to MySQL: " . mysqli_connect_error();
    die();
}
?>

Step 4 – Create a REST API File: Create an api.php file and copy the following script in it.

header("Content-Type:application/json");
if (isset($_GET['order_id']) && $_GET['order_id']!="") 
{
include('db.php');
$order_id = $_GET['order_id'];
$result = mysqli_query($con,
       "SELECT * FROM `transactions` WHERE order_id=$order_id");
if(mysqli_num_rows($result)>0)
       {
    $row = mysqli_fetch_array($result);
    $amount = $row['amount'];
           $response_code = $row['response_code'];
           $response_desc = $row['response_desc'];
    response($order_id, $amount, $response_code, $response_desc);
    mysqli_close($con);
}
       else
       {
     response(NULL, NULL, 200,"No Record Found");
}
}
else
{
response(NULL, NULL, 400,"Request is invalid");
}
function response($order_id,$amount,$response_code, $response_desc)
{
$response['order_id'] = $order_id;
$response['amount'] = $amount;
$response['response_code'] = $response_code;
       $response['response_desc'] = $response_desc;
$json_response = json_encode($response);
echo $json_response;
}
?>

The above code will accept the GET request and return output in the JSON format.

Now you can get an output as given below:

This is how you can create REST API in PHP.

31. What is PDO in PHP?

It gives a lightweight, vendor-neutral, data-access abstraction layer. Hence, no matter what database we use, the function to issue queries and fetch data will be the same. And, it focuses on data access abstraction instead of database abstraction.

32. Differentiate between GET and POST

33. Explain type hinting in PHP

Whenever the function is called, PHP checks if the arguments are of a user-preferred type or not. If the argument is not of the specified type, the run time will display an error and the program will not execute.

It is helpful in better code organization and improved error messages.

Example usage:

//sendEmail() function argument $email is type hinted of Email Class. It means to call this function you must have to pass an email object otherwise an error is generated.
function sendEmail (Email $email)
    {
      $email->send();
    }
?>

34. How to terminate the execution of a script in PHP?

The message which you want to display is passed as a parameter to the exit() function. Script termination will be done by this function after displaying the message. It is an alias of die() function. It doesn’t return any value.

Syntax: exit(message)

Where the message is a parameter to be passed as an argument. It defines a message or status.

Example: The code given below will print a message and exit the current script.

$site = "https://www.interviewbit.com//";
fopen($site,"r")
or exit("Unable to connect to $site");
?>