Best PHP Interview Questions And Answers

• It performs system functions, that is, from files in the system, it can create, open, read, write and close them.
• It can process forms, that is, collect data from files, save data to a file, send data by email, and return data to the user.
• You can add, remove, modify items in your database using PHP.
• Accessing Variable Cookies and Setting Cookies.
• Using PHP, you can restrict user access to certain pages of your site, as well as encrypt data.

PEAR is a framework and repository for reusable PHP components. PEAR stands for PHP Extension and Application Repository. It contains all types of PHP code snippets and libraries. It also provides a command line interface to automatically install "packages".

• On static websites, the content cannot be changed after the script is run. You cannot change anything on the site as it is predefined.
• On dynamic ones, the contents of the script can be modified at runtime. Its content is updated every time the user visits or reloads.

To execute a PHP script, use the PHP Command Line Interface (CLI) and specify the script file name as follows:

PHP script.PHP

PHP is partially case-sensitive. Variable names are case sensitive, but function names are not. If you define the function name in lowercase and call them in upper case, it will still work. UDFs are not case sensitive, but the rest of the language is case sensitive.

The PHP parsing engine needs a way to distinguish PHP code from other elements on the page. This mechanism is known as "switching to PHP". Escaping a string means reducing the ambiguity in quotes used in that string.

Some of the important characteristics of PHP variables include:

• All PHP variables are denoted by a leading dollar sign ($).
• The value of a variable is the value of its last assignment.
• Variables are assigned using the = operator, with the variable on the left and the expression to be evaluated on the right.
• Variables can, but need not be, declared before assignment.
• Variables in PHP do not have internal types - a variable does not know in advance whether it will be used to store a number or a string of characters.
• Variables used prior to their assignment have default values.

PHP has 8 data types that are used to create variables:

1. Integers are whole numbers without a decimal point, such as 4195.
2. Doubles are floating point numbers, such as 3.14159 or 49.1.
3. Booleans - have only two possible values: true or false.
4. NULL is a special type that has only one value: NULL.
5. Strings are sequences of characters, for example, "PHP supports string operations".
6. Arrays are named and indexed collections of other values.
7. Objects are instances of programmer-defined classes that can box both other value types and functions specific to that class.
8. Resources are special variables that contain references to resources external to PHP.

• The following rules must be followed when naming a PHP variable:

  • Variable names must begin with a letter or underscore.
  • A variable name can consist of numbers, letters, and underscores, but you cannot use characters such as +, -,%, (,). & , etc.

The rules for determining the "truth" of any value that is not yet Boolean are as follows:

• If the value is a number, it will be false if it is exactly zero, and true otherwise.
• If the value is a string, it will be false if the string is empty (contains null characters) or is the string "0", and true otherwise.
• NULL values ​​are always false.
• If the value is an array, it will be false if it contains no other values, and true otherwise. For an object containing a value, means that there is a member variable that has been assigned a value.
• Valid resources are true (although some functions that return resources on success return FALSE on failure).
• Don't use double booleans.

To define a constant, you must use the define() function, and to get the value of a constant, you just need to specify its name. Once you have defined a constant, it can never be changed or undefined. It is not necessary to have a constant with a $ symbol. A valid constant name begins with a letter or underscore.

• Break - ends the for loop or switch statement and transfers execution to the statement immediately after the for or switch loop.
• Continue - forces the loop to skip the rest of its body and immediately re-check its state before repeating.

The final keyword in a method declaration indicates that the method cannot be overridden by subclasses. A class declared final cannot be subclassed. This is especially useful when we are creating an immutable class such as the String class. Properties cannot be declared final, only classes and methods can be declared final.

We use the "==" operator to check if two objects are instances of the same class and have the same attributes and equal values. We can also check if two objects refer to the same instance of the same class using the "===" identity operator.

PHP and Javascript cannot communicate directly as PHP is a server-side language and Javascript is a client-side language. However, we can exchange variables as PHP can generate Javascript code to be executed by the browser and it is possible to pass certain variables back to PHP via a URL.

• It is possible to generate HTML using PHP scripts, and it is also possible to transfer pieces of information from HTML to PHP. PHP is a server-side language and HTML is a client-side language, so PHP is executed on the server-side and receives the results as strings, arrays, objects, and then we use them to display our values in HTML.

Some of the popular frameworks in PHP:

• CakePHP
• CodeIgniter
• Yii 2
• Symfony
• Zend Framework

The Include () function is used to put data from one PHP file into another PHP file. If errors occur, the include () function issues a warning but does not stop the script execution, and it will continue execution.

The Require () function is also used to put data from one PHP file into another PHP file. If there are any errors, the require () function will throw a warning and fatal error and stop the script execution.

Require () includes and evaluates a specific file, while require_once () does so only if it has not been included previously. The require_once () statement can be used to include a PHP file in another when you may need to include the called file more than once. So, require_once () is recommended when you want to include a file where you have a lot of functionality.

The foreach statement is used to loop through arrays. For each pass, the value of the current array element is assigned to $ value, the array pointer is moved by one, and the next pass will process the next element.

Syntax:

foreach (array as value)

{

code to be executed;

}

Example:

<?PHP

$colors = array("blue", "white", "black");

foreach ($colors as $value) {

echo "$value 

";

}

?>

PHP has 3 types of arrays:

• Indexed Array. An array with a numeric index is called an indexed array. The values ​​are stored and accessed linearly.
• Associative Array. An array with strings as an index is known as an associative array. In this case, the values ​​of the elements are stored together with the values ​​of the keys, and not in a strict linear order of the index.
• Multidimensional Array. An array containing one or more arrays is known as a multidimensional array. Values ​​are accessed using multiple indices.

Set_time_limit (0), added at the beginning of the script, sets an infinite execution time so that there is no PHP error "maximum execution time exceeded". This can also be specified in the PHP.ini file.

PHP is a programming language whereas ASP.NET is a programming environment. Websites developed by ASP.NET can use C# as well as other languages such as J#. ASP.NET is compiled and PHP is interpreted. ASP.NET is designed for Windows computers, whereas PHP is platformless and usually runs on Linux servers.

Overloading is the definition of functions that have similar signatures but different parameters. Overriding only applies to derived classes where the parent class has defined a method and the derived class wishes to override that method. In PHP, you can only overload methods with the __call magic method.

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

Basic steps to create a MySQL database using PHP:

• Establish a connection to the MySQL server from your PHP script.
• If the connection is successful, write a SQL query to create the database and store it in a string variable.
• Complete your request.

• PHP callbacks are functions that can be called dynamically by PHP. They are used by native functions like array_map, usort, preg_replace_callback, etc. A callback function is a function that you create yourself and then pass to another function as an argument. After accessing your callback function, the receiving function can call it at any time.

  Here's a basic example of a callback function:

  <?PHP

  function thisFuncTakesACallback($callbackFunc)

  {

  echo "I'm going to call $callbackFunc!

  ";

  $callbackFunc();

  }

  function thisFuncGetsCalled()

  {

  echo "I'm a callback function!

  ";

  }

  thisFuncTakesACallback( 'thisFuncGetsCalled' );

  ?>

PHP provides the cURL library, which is probably already included in the default PHP installation. cURL stands for Client URL and it allows you to connect to the URL and get information from that page, such as the HTML content of the page, HTTP headers, and related data.

An exception that is thrown at compile time is called a checked exception. This exception cannot be ignored and must be handled with care. For example, if you use the FileReader class to read data from a file, and the file specified in the class constructor does not exist, a FileNotFoundException is thrown and you have to handle that exception. To do this, you will need to write code in a try-catch block and handle the exception. On the other hand, an exception thrown at runtime is called an unchecked-exception.