Ans. A variable in PHP is a symbol or name that represents a value. Variables are declared with a dollar sign ($) followed by the variable name. For example, $myVariable = "Hello, PHP!"; creates a variable named myVariable that holds the string value "Hello, PHP!".

Ans. An array in PHP is a data structure that can hold multiple values in a single variable. PHP supports both indexed arrays (with numeric keys) and associative arrays (with named keys). For example:

$indexedArray = array(1, 2, 3);
$associativeArray = array("key1" => "value1", "key2" => "value2");

Ans. A function in PHP is a block of code that performs a specific task and can be reused throughout the program. Functions are defined using the function keyword. For example:

function myFunction() {
    echo "Hello from myFunction!";
}

Ans. An object in PHP is an instance of a class. Objects can contain both data (properties) and functions (methods) that operate on the data. Object-oriented programming in PHP allows for encapsulation, inheritance, and polymorphism. For example:

class MyClass {
    public $property;

    public function myMethod() {
        echo "Hello from myMethod!";
    }
}

$myObject = new MyClass();
$myObject->property = "Some value";

Ans. A string in PHP is a sequence of characters enclosed in single quotes (') or double quotes ("). Strings can be manipulated using various built-in functions. For example:

$myString = "Hello, World!";
echo strlen($myString); // Outputs the length of the string

Ans. Superglobals are built-in global arrays in PHP that are always accessible, regardless of scope. Common superglobals include $_GET, $_POST, $_SESSION, and $_COOKIE. They are used to handle form data, session management, and more.

Ans. Error handling in PHP involves managing errors that occur during script execution. PHP provides several functions for error handling, such as try, catch, and throw for exceptions. You can also set custom error handlers using set_error_handler() to define how errors should be handled.

Ans. Both echo and print output data to the screen. However, echo can take multiple parameters and is slightly faster, while print returns a value (1), so it can be used in expressions.

Ans. == checks for value equality regardless of type, while === checks for both value and data type equality.

Ans. PHP sessions are used to store user information across multiple pages. They maintain user state by storing data on the server using the $_SESSION superglobal.

Ans. Cookies store data on the client’s browser, while sessions store data on the server. Cookies persist after the browser is closed (based on expiration), while session data is typically lost when the session ends.

Ans. You can connect using mysqli_connect() or PDO. Example using mysqli:
$conn = mysqli_connect("localhost", "username", "password", "database");

Ans. PDO (PHP Data Objects) is a database access layer providing a uniform method of access to multiple databases, supporting secure and flexible database interactions.

Ans. Magic methods are special functions in PHP that start with __, like __construct(), __destruct(), __get(), __set(), and __toString(). They are automatically called in certain scenarios.

Ans. A constructor (__construct()) is called when an object is created. A destructor (__destruct()) is called when the object is destroyed or the script ends.

Ans. PHP handles exceptions using try, catch, and optionally finally blocks. throw is used to trigger exceptions manually.

Ans. These functions are used to include files. require causes a fatal error if the file is missing; include gives a warning. The _once versions prevent multiple inclusions.

Ans. GET appends data to the URL and is suitable for non-sensitive data. POST sends data in the HTTP body and is used for secure or large data submissions.

Ans. Namespaces help avoid name conflicts in larger applications by encapsulating classes, functions, and constants. Defined using the namespace keyword.

Ans. PHP uses the mail() function to send emails. For example: mail($to, $subject, $message, $headers);

Ans. isset() checks if a variable is set and not null, while empty() checks if a variable has a "falsy" value like 0, "", null, or false.

Ans. Traits are a mechanism for code reuse in single inheritance languages. A trait allows developers to reuse sets of methods in multiple classes.

Ans. Type hinting specifies the expected data type of function arguments and return values, enhancing code clarity and reducing bugs.

Ans. Use prepared statements with PDO or MySQLi to safely handle user inputs and avoid SQL injection attacks.

Ans. Output buffering allows you to store output data in an internal buffer instead of immediately sending it to the browser. Useful for headers and performance.

Ans. Use the header() function to redirect: header("Location: page.php"); followed by exit;.

Ans. Composer is a dependency manager for PHP. It allows you to manage project libraries and automatically install or update packages.

Ans. PHP supports public, private, and protected modifiers to control access to class members.

Ans. Autoloading automatically includes class files when objects are instantiated. It’s commonly handled using spl_autoload_register() or Composer.

Ans. Common practices include input validation, output sanitization, using prepared statements, setting proper permissions, using HTTPS, and keeping PHP and dependencies up to date.

Ans. The explode() function splits a string into an array using a delimiter. Example:
$arr = explode(",", "apple,banana,orange");

Ans. Static websites show the same content to all users, while dynamic websites generate content based on user interaction, often using PHP to fetch and display data dynamically.

Ans. isset() checks if a variable is set and is not null. It returns true if the variable exists and is not null.

Ans. You define a constant using the define() function:
define("SITE_NAME", "MyWebsite");

Ans. Interfaces allow you to define methods that must be implemented in a class. They support abstraction and help in designing loosely coupled systems.

Ans. An abstract class can have method implementations, while an interface cannot. A class can implement multiple interfaces but only extend one abstract class.

Ans. The final keyword prevents a method from being overridden or a class from being inherited.

Ans. header() sends raw HTTP headers to the browser. It is commonly used for redirection, content type, or caching headers.

Ans. Use the date() function:
echo date("Y-m-d H:i:s");

Ans. A callback is a function passed as an argument to another function, often used in array functions like array_map(), usort(), etc.

Ans. unset() destroys a variable, while unlink() deletes a file from the file system.

Ans. A while loop checks the condition before execution, whereas do-while executes the block at least once before checking the condition.

Ans. die() prints a message and terminates script execution. It's commonly used for error handling.

Ans. Use session_start(); at the beginning of the script to start a session and access $_SESSION variables.

Ans. Use session_destroy(); to end a session and clear session data.

Ans. Use fopen() to create or open a file. For example:
$file = fopen("newfile.txt", "w");

Ans. You can use fread(), fgets(), or file_get_contents() depending on the need. Example:
$content = file_get_contents("file.txt");

Ans. Use fwrite() after opening a file in write mode. Example:
fwrite($file, "Hello, file!");

Ans. Variables declared outside a function are global. Use the global keyword inside functions to access them.

Ans. $_SERVER is a superglobal that provides information about headers, paths, and script locations. Example:
$_SERVER['HTTP_USER_AGENT'] gives the user's browser info.

Ans. Both require and include are used to include and evaluate files. The difference is that require causes a fatal error if the file is not found, whereas include only raises a warning.

Ans. GET appends data to the URL and has length restrictions, while POST sends data in the request body, making it more secure for sensitive data.

Ans. Magic constants are predefined constants like __LINE__, __FILE__, __DIR__, __FUNCTION__, etc., that change depending on where they are used.

Ans. Traits are a mechanism for code reuse in single inheritance. A trait is similar to a class, but it is intended to group functionality in a fine-grained and consistent way.

Ans. public members are accessible from anywhere, private only within the class, and protected within the class and its subclasses.

Ans. filter_var() filters a variable with a specified filter, like validating emails or sanitizing strings. Example:
filter_var($email, FILTER_VALIDATE_EMAIL);

Ans. PHP has functions like error_reporting(), set_error_handler(), and exception handling with try-catch blocks.

Ans. A session is stored on the server, while a cookie is stored in the user's browser. Sessions are more secure than cookies for storing sensitive data.

Ans. Both are used for accessing databases. mysqli is specific to MySQL, while PDO supports multiple databases and provides an abstraction layer.

Ans. Use prepared statements with bound parameters (e.g., using mysqli_prepare() or PDO::prepare()) to prevent SQL injection.

Ans. echo can output multiple strings and is slightly faster. print returns a value (1), so it can be used in expressions.

Ans. Associative arrays use named keys. Example:
$person = array("name" => "John", "age" => 30);

Ans. == compares values after type juggling, while === checks both value and type.

Ans. var_dump() displays structured information about a variable, including type and value. Useful for debugging.

Ans. Anonymous functions are functions without a name, often used as callbacks:
$greet = function($name) { return "Hello $name"; };

Ans. Use the header("Location: page.php"); function to redirect. Ensure no output is sent before calling it.

Ans. Output buffering allows you to capture output and control when it is sent to the browser using functions like ob_start() and ob_get_clean().

Ans. include() includes a file every time it's called, while include_once() includes it only once, preventing multiple inclusions.

Ans. Autoloading allows classes to be loaded automatically when needed using spl_autoload_register(), avoiding manual require statements.

Ans. Namespaces help avoid name conflicts by encapsulating classes, functions, and constants. Declared using namespace keyword.

Ans. Composer is a dependency manager for PHP. It allows you to install and manage libraries your project depends on.

Ans. PSR stands for PHP Standard Recommendation. It's a set of coding standards and best practices accepted by the PHP-FIG group.

Ans. A closure is an anonymous function that can capture variables from the surrounding scope using the use keyword.

Ans. Superglobals are built-in variables like $_GET, $_POST, $_SESSION, $_SERVER, and $_COOKIE that are available in all scopes.

Ans. htmlspecialchars() converts special characters to HTML entities, while htmlentities() converts all applicable characters to entities.

Ans. list() is used to assign values to a list of variables in one operation. Example: list($a, $b) = array(1, 2);

Ans. array_merge() merges multiple arrays. array_combine() creates an array using one array for keys and another for values.

Ans. explode() splits a string by a delimiter. str_split() splits a string into an array of characters or fixed-length segments.

Ans. Use the mail() function: mail($to, $subject, $message, $headers);

Ans. Common error types: Parse errors, Fatal errors, Warning, Notice, and Deprecated warnings.

Ans. instanceof checks if an object is an instance of a specific class or implements an interface.

Ans. Use the extends keyword to create a subclass from a parent class.

Ans. Use array_key_exists() or isset() if you're checking for set and non-null keys.

Ans. file_get_contents() reads a file into a string. fread() reads a file resource with a defined length.

Ans. A recursive function calls itself to solve smaller instances of the same problem, useful in tree or directory traversal.

Ans. Both return the number of elements in an array. sizeof() is an alias of count().

Ans. Use the const keyword inside a class:
class MyClass { const VERSION = '1.0'; }

Ans. get_class() returns the name of the class of an object.

Ans. A generator allows you to iterate over a set of data without needing to build an array in memory using yield.

Ans. Interface defines a contract, while traits provide reusable method implementations. Classes can implement multiple interfaces and use multiple traits.

Ans. Static methods belong to the class rather than an instance and are declared using the static keyword.

Ans. Type hinting allows you to specify the expected data types for arguments, return values, and properties in functions and methods.

Ans. ?? is the null coalescing operator. It returns the left operand if it exists and is not null; otherwise, it returns the right operand.

Ans. The <=> operator returns -1, 0, or 1 when the left side is respectively less than, equal to, or greater than the right side.

Ans. Use json_decode() to parse JSON into a PHP array or object.

Ans. Use json_encode() to convert PHP arrays or objects into a JSON string.

Ans. __destruct() is a method called when there are no other references to a particular object, used for cleanup.

Ans. __construct() is a constructor method that initializes object properties when the object is created.

Ans. Use the empty() function to check if a variable is empty (i.e., "", 0, null, false, [], etc.).

Ans. isset() checks if a variable is set and not null. empty() checks if a variable has an empty value.