En kalender i php

<?
if ($_GET['mdr'] == null) {
$dag = date("d");
$mdr = date("m");
$ar = date("Y");
}
else {
$dag = date("d");
$mdr = $_GET['mdr'];
if ($_GET['ar']) { $ar = $_GET['ar']; } else { $ar = date("Y"); }
}
$mdr_start = mktime(0,0,0,$mdr, 1, $ar);
$mdr_navn = date('M', $mdr_start);
$mdr_start_dag = date('D', $mdr_start);
$dage = cal_days_in_month(0,$mdr,$ar);
if ($mdr == 12) { $ar_frem = ($ar + 1); $next_page = "1"; } else { $next_page = ($mdr + 1); }
if ($mdr == 1) { $ar_prev = ($ar - 1); $prev_page = "12"; } else { $prev_page = ($mdr - 1); }
echo '<table width="35%" border="0">';
echo '<tr><td width="10%"><a href="?p=kal&mdr='.$prev_page.'';
if ($ar_prev) { echo '&ar='.$ar_prev.''; }
elseif ($_GET['ar']) { echo '&ar='.$_GET['ar'].''; }
echo '">Tilbage</a></td>'.$dag.'-'.$mdr.'-'.$ar.'</td><td>
<a href="?p=kal&mdr='.$next_page.'';
if ($ar_frem) { echo '&ar='.$ar_frem.''; }
elseif ($_GET['ar']) { echo '&ar='.$_GET['ar'].''; }
echo '">Frem</a></td></tr>';
echo '<tr><td width="5%">Man</td><td width="5%">Tirs</td><td width="5%">Ons</td><td width="5%">Tors</td><td width="5%">Fre</td><td width="5%">Lør</td><td width="5%">Søn</td></tr><tr>';
switch($mdr_start_dag){
case "Mon": $set = 0; break;
case "Tue": $set = 1; break;
case "Wed": $set = 2; break;
case "Thu": $set = 3; break;
case "Fri": $set = 4; break;
case "Sat": $set = 5; break;
       case "Sun": $set = 6; break;
}
$week_day = 0;
while($week_day < $set) {
echo '<td> </td>';
       $week_day++;
}
$week_day = $set;
$day_counter = 1;
while($day_counter <= $dage) {
if ($week_day == 7) {
echo '</tr><tr>';
       $week_day = "0";
       }
       if ($dag == $day_counter and $mdr == date("m")) {
       echo '<td><b>'.$day_counter.'</b></td>';
       }
       else {
       echo '<td>'.$day_counter.'</td>';
       }
       $week_day++;
       $day_counter++;
       }
echo '</tr></table>';

?>