$ _Get变量不起作用

Question

I'm Jad and I'm trying to make a math rounder. The problem is that when I click Do Math!, the echo doesn't work. Here's my code:

<?php
if(isset($_GET['math']))
    switch ($_GET['math']) {
        case "round":
            if (isset($_POST['submit'])){
                echo round($_POST['numb1']); 
            } else{
                ?>
                <h1>Math Rounding!</h1>
                <form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">         
                    <table border="0">
                        <tr>
                           <td>Number:</td>
                           <td>
                               <input type="text" name="numb1" placeholder="Number 1..." maxlength="44444444444444444444444444444444444444444444444444444444444444444444">
                           </td>
                       </tr>
                       <tr>
                           <th colspan=2>
                              <input type="submit" name="submit" value="Do Math!" style="height: 25px; width: 100px">
                           </th>
                      </tr>
                    </table>
                </form>
                </center>
                <?php 
        break;
    }
}
?>

Answer 1

So in each form change the value of hidden field(<input type="hidden" name="math" value="round">) acoordingly.and also need to change the forms action to a single page.

<?php
if(isset($_POST['math']))
{
switch ($_POST['math'])
{
case "round":

echo round($_POST['numb1']);
exit;
case "round1":
echo round($_POST['numb1']);
exit;

}
 }      
else{
?>
<h1>Math Rounding!</h1>
<form action="<?php
echo $_SERVER['PHP_SELF'];
?>" method="post">


<input type="hidden" name="math" value="round">


<table border="0">
<tr><td>Number:</td><td>
<input type="text" name="numb1" placeholder="Number 1..." maxlength="44444444444444444444444444444444444444444444444444444444444444444444">
</td></tr>
<tr><th colspan=2><input type="submit" name="submit" 
value="Do Math!" style="height: 25px; width: 100px"></th></tr></table>
</form>
</center>
<?php 


}?>