I have made a function inside the themes PHP file that i am using

public function numberAdd($start,$end) {
		for($x=$start;$x<=$end;$x++){
			echo '<option value=',$x,'>',$x,'</option>';
		}
	}

And I call it in the .ss file, trying to add it to a drop down menu with:

<select name="day">
<option value="">Day</option>
$numberAdd(1,31);
</select>

However when I open the page, all of the numbers that should be appearing as part of the list, are just appearing as plain text above all of the other stuff on the site, what am I doing wrong here?
Thanks

You need to return a value with your function, rather than echoing the values, i.e. something like this:

        public function numberAdd($start, $end) {
                $optionsHTML = '';
                for ($x = $start; $x <= $end; $x++) {
                        $optionsHTML .= '<option value=' . $x . '>' . $x . '</option>';
                }
                return $optionsHTML;
        }