Explain the differences between GET and POST methods in the context of HTTP protocol and web applications.

GET and POST methods are two main HTTP methods used for client-server interaction.

GET:

• Used to request data from the server.
• Parameters are passed in the URL (query string).
• Requests can be cached and stored in the browser history.
• Not intended for transmitting large amounts of data or confidential information.

POST:

• Used to send data to the server (e.g., forms).
• Data is transmitted in the body of the HTTP request.
• Not cached or stored in browser history.
• Allows transmitting large amounts of data and files.

Example in PHP:

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $username = $_POST['username'];
    // process form data
} else {
    // process GET request
}