The case keyword in a PHP switch statement represents a possible value for the expression. Each case block represents a specific value or condition that is evaluated against the switch expression. When a case value matches the expression, the corresponding block of code is executed. The case keyword allows you to define multiple possible values or conditions to be compared within the switch statement. Each case represents a potential match with the expression. Learn more: https://www.php.net/manual/en/control-structures.switch.php

In PHP, you can call a user-defined function using a string variable by using the variable as the function name followed by parentheses () or curly brackets {}. For example, if $function_name is a string variable containing the function name, you can call the function like $function_name(). The other mentioned options are not valid syntax for calling a function using a string variable in PHP. For further details, refer to the PHP documentation on variable functions: http://php.net/manual/en/functions.variable-functions.php

To use image functions in PHP, you need to have the GD (Graphics Draw) library enabled. The GD library is a popular image manipulation library that provides a set of functions to create, modify, and output images. It supports various image formats and allows you to perform operations like resizing, cropping, adding text, and applying filters to images. The GD library needs to be installed and enabled in your PHP configuration for the image functions to work.

In PHP, you can start a session by using the session_start() function. This function initializes a new session or resumes an existing session. It needs to be called at the beginning of your PHP script before any session variables are accessed. Refer to: http://php.net/manual/en/function.session-start.php

PHP is a powerful server-side scripting language designed for web development but also used as a general-purpose programming language. This means PHP code is executed on the server, generating HTML which is then sent to the client's browser. PHP can create, open, read, write, delete, and close files on the server, collect form data, send and receive cookies, and much more. For further information, check: https://www.php.net/intro-php.php

The correct option is 1. The asort() function in PHP sorts an associative array in ascending order based on its values. It rearranges the elements of the array while maintaining the association between keys and values. After sorting, the keys remain associated with their corresponding values. This is useful when you need to sort an associative array based on the values while preserving the relationship between keys and values. The original key-value association is retained after the sorting operation. Learn more: https://www.php.net/manual/en/function.asort.php

The correct option is 4. When working with superglobals in PHP, potential issues can arise. Insecure usage of superglobals, such as $_POST or $_GET, can lead to security vulnerabilities, such as injection attacks or data tampering. It is crucial to properly validate and sanitize any data obtained from superglobals before using it. Another potential issue is unexpected data manipulation due to variable scoping. Modifying the values of superglobals directly can have unintended consequences, as they are accessible from various parts of the script. Additionally, there can be naming conflicts with user-defined variables if they have the same name as a superglobal, leading to unexpected behavior. It is important to handle superglobals with caution, following best practices to ensure the security and integrity of the application. Learn more: https://www.php.net/manual/en/language.variables.superglobals.php

The purpose of the if statement in PHP is to conditionally execute a block of code based on a specified condition. It allows you to make decisions in your code by evaluating a condition and executing different code blocks depending on whether the condition is true or false. The if statement is a fundamental control structure in PHP and is used extensively for implementing logic and flow control in scripts. By using if statements, you can create dynamic and responsive code that reacts to different scenarios. Learn more: https://www.php.net/manual/en/control-structures.if.php

In PHP, Form Handling involves collecting, processing, and responding to user data submitted through HTML forms. HTML forms provide a way for users to input and submit data, which is then sent to the server for processing. PHP provides various functions and techniques to handle the form data and perform actions such as validation, sanitization, storage, or further processing. The data submitted through HTML forms can be accessed in PHP using superglobal arrays like $_POST or $_GET, depending on the form's method attribute. Form Handling in PHP is a crucial aspect of building interactive websites and web applications. Learn more: https://www.php.net/manual/en/tutorial.forms.php

In PHP, the echo statement can output one or more strings. It is commonly used to display strings and variables. You can use echo to output plain text, HTML code, or a combination of both. Multiple strings can be concatenated with the dot (.) operator within the echo statement. Learn more: https://www.php.net/manual/en/function.echo.php