Something

<?php
foreach ($_POST as $key => $value) {
	// assign to temporary variable and strip whitespace if not an array
	$temp = is_array($value) ? $value : trim($value);
	// if empty and required, add to $missing array
	if (empty($temp) && in_array($key, $required)) {
		$missing[] = $key;
	
	} elseif (in_array($key, $expected)) {
	// otherwise, assign to a variable of the same name as $key
	${$key} = $temp;
	}
}