Calendar code

[yogabasics]

I modified this code that I found elsewhere and it works unless it is at the end of the month.  At the end of the month if you click on a day that is in the next month things get all screwy.  I also need to know how to make the days of the week always code to future dates and I think that would fix the problems that happen at the end of the month.  Here is the code:

<?php
$cal_url = 'http://www.mywebsite.com/yoga-classes?calendar=2&category=0&d=';

$wd_arr = array('Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday');
$monday = mktime(0, 0, 0, // hour, minute, second
(int)date('m'), // month
(int)date('d')+(1-(int)date('w')), // day (can be negative!)
(int)date('Y')); // year

for ($n=0; $n<7; $n++) {
echo "<a href='$cal_url", date('d', $monday+$n*60*60*24), "&m=", date(m), "&Y=", date(Y),  "'>", $wd_arr[$n],  "</a>  ";
}
?>