Calculating Discounts

Today we found an interesting bug in the software when discounts are applied to the transaction.

Here is an example.

Variables
  ItemPrice = 50.00
  Discount  = 14.49%

Calculate Discount Value (DisValue)
  DisValue  = ItemPrice * (Discount/100)
  DisValue  = 50.00 * (14.49/100)
  DisValue  = 50.00 * 0.1449
  DisValue  = 7.245

Calculate NewPrice
  NewPrice  = ItemPrice - DisValue
  NewPrice  = 50.00 - 7.245
  NewPrice  = 42.755

At this point we need to round the values, becuase prices have two decimal places. There are two options, we can either round the values up or down.

Round Up Values
  NewPrice = 42.76
  DisValue =  7.25
  Total    = 50.01 (1p over)

Round Down Values
  NewPrice = 42.75
  DisValue =  7.24
  Total    = 49.99 (1p under)

As you can see, when we add up the rounded totals, they do not match the original item price. So we need find a way to solve this problem.

Two Jobs

Yes I now have two jobs!

Mode is now its own company and I've just started part time in a support role. I may also do some occasional development work.

I don't know if I should revive my old blog.

New Guinness

There is a new Guinness pint coming to a pub near you.

Guinness Red!

Can't wait to give it a try.