js math and variable problem

[indiguy]

Cost = 0 , Grand_Total = 0, Product="";
function additem(Item_id, Price, Choice)
{
 // var Choice = new Array(); 
if(Item_id.checked==true) 
{ 
Cost = Cost++ + Price; 
Cost = dollar(Cost); 
Grand_Total = parseFloat(Cost);
Product = Product + Choice;
}
if(Item_id.checked==false) 
{ 
Cost = Cost-- - Price; 
Cost = dollar(Cost); 
Grand_Total = parseFloat(Cost);
Choice=Choice.replace(/\+/g," "); 
Product = Product - Choice;
}
document.order.GrandTotal.value = "$" + Grand_Total;
document.order.Cart.value = Product;
}
// format the dollar rounding of zeros
function dollar (amount)
{
 amount = parseInt(amount * 100);
 amount = parseFloat(amount/100);
 if (((amount) == Math.floor(amount)) && ((amount - Math.floor (amount)) == 0))
 {
  amount = amount + ".00"
  return amount;
 }
 if ( ((amount * 10) - Math.floor(amount * 10)) == 0)
 {
  amount = amount + "0";
  return amount;
 }
 if ( ((amount * 100) - Math.floor(amount * 100)) == 0)
 {
  amount = amount;
  return amount;
 }
 return amount;
}

This takes the price of a item and prints out the total.
Problem 1.
If current total from a couple of items are 6.90
when i remove an item $4.40
it totals $2.49 instead of $2.50 It will end up a -0.01 if i remove everything.

Problem 2.
Im passing the item names through the JS.
should that be an array?
I dont know how to print it out into the current page so they can see a list with the total. (no textbox wanted either as ive been testing with)

Can anyone help please... im no js expert.

[tomda]

Problem 1 - Sorry, I am not a math guru... even less in js... but use alert() to debug your dollar function.

Problem 2 - An array would be better indeed, especialy if there are more than one items. But note that usually, when I deal with basket, I prefer to use raw text file using PHP, a tmp file that I create, update adn parse when necessary.

To print out JS result look for document.getElementById(containerid).innerHTML. As always, this is one alternative...

document.getElementById(containerid).innerHTML = '<b><i>This is my result:</i> '+amount+' USD</b>';

My 2 cents

[rocknbil]

....it totals $2.49 instead of $2.50 It will end up a -0.01 if i remove everything.

Without testing your code, this is most likely a floating point precision issue, one that's driven me bonkers on occasion.

Here's a thread [webmasterworld.com] exploring the issue and some solutions.

The short story: toFixed() will resolve the one penny conundrum.