- in_array: documentation ( source)
<?php
$regSecond = 30;
$setA = array('00', '01', '02', '06', '07', '08', '09', '10', '11', '12', '13', '14', '15',
'16', '17', '18', '30', '31', '32', '33', '34', '35', '36', '37', '38', '39', '40', '41', '42', '43');
if (in_array($regSecond, $setA)) {
echo 'Set A';
}