php switch statement using text box/drop down box -

i trying use switch statement make when specific word typed text box display available models of car

for example

if user entered "volkswagen" should echo "the available models beetle , polo"

but reason isnt working can suggest me why?

here code have far,

<form action="switch.php" method="post">      <input type="text" name="cars" id="cars" />        <input type="submit" />  <?php $i = $_post; ?>  <?php switch ($i) {     case "volkswagen":         echo "the available models beetle , polo";         break;     case "renault":         echo "the available models megane , clio";         break;     case "land rover":         echo "the available models range rover sport , defender";         break; } ?> </form>  

edit:

i bit stuck trying use switch statement drop down box , not quite sure how can make them work if can me make them work great

this code have working switch , working drop box.

<form action=""> <select name="cars"> <option value="volkswagen">volkswagen</option> <option value="renault">renault</option> <option value="land rover">land rover</option> </select>   <p> <?php switch($_post['cars']) {     case "volkswagen":         echo "the available models beetle , polo";         break;     case "renault":         echo "the available models megane , clio";         break;      case "land rover":         echo "the available models range rover sport , defender";         break; } ?> </p> </form> </center> 

$_post array. not can compare against strings. php convert array literal word array. since don't have case word, no matches @ all.

form values submitted elements of $_post array. should doing

switch($_post['cars']) {    ... } 

instead