打印某年某月的天数

<?php
header ( 'Content-type:text/html;charset=utf8' );
$m = isset ( $_GET ['month'] ) ? intval ( $_GET ['month'] ) : date ( 'm' );
$y = isset ( $_GET ['year'] ) ? intval ( $_GET ['year'] ) : date ( 'Y' );
?>
<form method="get" id="form">年<select id="year" name="year"
     onchange="document.getElementById('form').submit()">
<?php

for($i = 1949; $i < 2050; $i ++) {
    
     if ($i == $y)
          echo '<option value=' . $i . ' selected>' . $i . '</option>';
     else
          echo '<option value=' . $i . '>' . $i . '</option>';
}
?>
</select> 月 <select id="month" name="month"
     onchange="document.getElementById('form').submit()">
<?php

for($i = 1; $i <= 12; $i ++) {
     if ($i == $m)
          echo '<option value=' . $i . ' selected>' . $i . '</option>';
     else
          echo '<option value=' . $i . '>' . $i . '</option>';
}
?>
</select> 日： <select id="day">
<?php

$monthArr = array ('January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December' );
$month = $monthArr [$m - 1];
$time = strtotime ( $month . ' ' . $y );
$days = date ( 't', $time );
for($i = 1; $i <= $days; $i ++) {
     echo '<option value=' . $i . '>' . $i . '</option>';
}
?>
</select></form>