Defining And Display Variables With Switch Statement

I'm trying to code a script that will display an approximate postage price based on different combinations of variables, but the numbers I defined for each case aren't reflected in the text box. I'm using a switch statement for all the different combinations of options, which the user will choose by selecting check-boxes. (Additionally, I know that this code probably isn't a very efficient way of doing what I'm doing - how to improve it.) I've attached all the relevant parts of the code, including how I defined variables originally.

<script type="text/javascript">
function count(){
var firstclass = document.calc.firstclass.value;
var postcard = document.calc.firstclass.value;
var numpages = document.calc.numpages.value;
var nms = document.calc.nms.value;
var large = document.calc.large.value;
var numpages = parseInt(document.calc.numpages.value); .....