PHP分支控制语句 if...else 和 switch

if...else 语句实例：

<?php
$t=date("H");
if ($t<"10")
{
    echo "Have a good morning!";
}
else if ($t<"20")
{
    echo "Have a good day!";
}
else
{
    echo "Have a good night!";
}
?><?php
$t=date("H");
if ($t<"1