case_study_08.php

<?php

$users = [
    'user1@example.com' => 'Adimas Lutfi Wicaksono',
    'user2@example.com' => 'Salman Alfarisi',
    'user3@example.com' => 'Muhammad Sholeh',
    'user4@example.com' => 'Yadi Cahyadi',
    'user5@example.com' => 'Maya Maulani',
];

foreach ($users as $key => $value)
{
	$emails[] = $key;
}

print_r($emails);