What are the steps to modify the existing PHP code to include user session data in a form for pre-filling user information?

To pre-fill user information in a form, we need to retrieve the user session data and populate the form fields with this information. This can be achieved by accessing the session variables that store user data and setting the default values for the form fields using these variables.

<?php
session_start();

// Check if user is logged in and session data exists
if(isset($_SESSION['user_id'])) {
    $user_id = $_SESSION['user_id'];
    $username = $_SESSION['username'];
    $email = $_SESSION['email'];
    
    // Set default values for form fields
    $username_value = isset($username) ? $username : '';
    $email_value = isset($email) ? $email : '';
}

?>

<form action="update_profile.php" method="post">
    <label for="username">Username:</label>
    <input type="text" id="username" name="username" value="<?php echo $username_value; ?>" required><br><br>
    
    <label for="email">Email:</label>
    <input type="email" id="email" name="email" value="<?php echo $email_value; ?>" required><br><br>
    
    <input type="submit" value="Update Profile">
</form>