Objective: $$ To create a PHP web application that: $$ Collects user data through an HTML form. $$ Validates user input on the server$-$side using PHP$.$ Stores validated data in a text file. $$ Retrieves and displays stored user data on a separate page. Materials: $$ Computer with Windows, macOS, or Linux operating system $$ XAMPP platform $$ Text editor $($e$.$g$.,$ Notepad$++,$ Sublime Text, Visual Studio Code$)$ Procedure: Part $1$: HTML Form Creation : o Design and Create an HTML form with the following fields : $$ Name: A required text input field $.$ Email: A required email input field $.$ Phone Number: A required number input field for $10-$digit. $$ Message: An optional text area field for user messages. $$ Add more fields if you can with appropriate validation. Part $2$: Server$-$Side Validation with PHP : o Receive Form Data: Use PHP$\text{'}$s $$\_$POST superglobal array to access form data $.$ o Input Validation: Implement server$-$side validation using PHP functions : o Name: Check if the name field is empty $.$ o Email: Verify the email format using filter$\_$var$()$ with FILTER$\_$VALIDATE$\_$EMAIL $.$ o Phone Number: Ensure it's a $10-$digit number using preg$\_$match $.)($ o Error Handling: Display appropriate error messages for invalid input $.$ Part $3$: Data Storage : o File Writing: Open a text file in append mode $("$a$")$ to add new user data without overwriting existing entries $.$ o Data Formatting: Format the data before writing to the file. $$ For example, use a comma$-$separated format : $$ name,email,phone$\_$number,message o File Closing: Close the file after writing to ensure data integrity $.$ Part $4$: Data Retrieval and Display: o File Reading: Open the text file in read mode $("$r$").$ o Data Parsing: Read the file line by line, parsing each line to extract user information $.$HTML Table Generation: Create an HTML table to display the retrieved data in a structured format $.$ o Page Rendering: Render the HTML page with the populated table. Additional Considerations: $$ Security: o Sanitize and validate user input to prevent security vulnerabilities like SQL injection and XSS attacks. o Consider using prepared statements or parameterized queries if working with databases. $$ Error Handling: o Implement robust error handling to gracefully handle exceptions and unexpected input. o Provide clear and informative error messages to the user. $$ User Experience: o Use clear and concise form labels and instructions. o Provide visual feedback to indicate input validity or errors. o Consider using a front$-$end framework $($e$.$g$.,$ Bootstrap, Tailwind CSS$)$ to improve the user interface. $$ File Storage: o For larger applications, consider using a database to store user data. o Implement appropriate file permissions to protect sensitive information. By following these guidelines and incorporating best practices, you can create a secure$,$ user$-$friendly, and robust web application that effectively collects, validates, stores, and retrieves user data. Additional Tips: $$ Use meaningful variable names. $$ Indent your code properly to improve readability. $$ Add comments to explain complex parts of your code. $$ Test your code thoroughly to ensure it works as expected. $$ Refer to the PHP documentation for more information and examples.