Code for area

$iloveshapes = $_POST['shape'];
echo $iloveshapes;
if($iloveshapes=="circle")
{
//formula for area of square
echo (($_POST['length']*$_POST['length'])*3.1416);

}
else
{
//we need the radius of the circle
echo "Does this work?";
echo $_POST['length']* $_POST['length'];
//pi*r to the second power