How can the unsatisfactory programming structure of the provided code be improved to ensure cleaner and more efficient functionality?

The unsatisfactory programming structure of the provided code can be improved by implementing object-oriented programming principles. This will help in organizing the code into classes and methods, making it cleaner and more efficient. By creating separate classes for different functionalities and using methods to encapsulate specific tasks, the code will be easier to maintain and understand.

class User {
    private $username;
    private $email;

    public function __construct($username, $email) {
        $this->username = $username;
        $this->email = $email;
    }

    public function getUsername() {
        return $this->username;
    }

    public function getEmail() {
        return $this->email;
    }
}

$user1 = new User("JohnDoe", "johndoe@example.com");
echo $user1->getUsername();
echo $user1->getEmail();