If you are not already using views, you should consider it, but here's a simple example how to pass data to view and then in view display different HTML, depending on values.
Controller:
PHP Code:
public function index()
{
// ...
$showRegistrationButton= false;
// data to pass to view
$data = [
'showRegistrationButton' => $showRegistrationButton,
'pageTitle' => 'My page title'
];
$this->load->view('myview', $data);
}
View file:
PHP Code:
<h1><?= $pageTitle ?></h1>
<?php if ($showRegistrationButton) : ?>
<a href="<?= site_url('registration-controller') ?>">Register</a>
<?php else: ?>
<div>Already registered</div>
<?php endif ?>
