Re: Currency Rounding Errors

From:

"Jonathan Wood" <jwood@softcircuits.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Fri, 17 Apr 2009 10:44:31 -0600

Message-ID:

<eIeXMv3vJHA.5836@TK2MSFTNGP06.phx.gbl>

Thinking about this further, I guess I could eliminate this specific problem
by simply rounding off anything after the cents as I sum the values.

Does that seem like the best approach? I'm worried this will still cause
problems in other reports I'm creating. In some cases, I use the database to
total the values and so I wouldn't be able to apply the same technique.

"Jonathan Wood" <jwood@softcircuits.com> wrote in message
news:etqC%23r3vJHA.4980@TK2MSFTNGP02.phx.gbl...

I don't know if there are any math-programming experts here.

I have a program that works with currency values. In order to avoid
rounding errors, I'm storing my currency values as 64-bit integers. Values
are stored as the number of cents multiplied by 100. As I understand it,
this is how the COM currency routines work, which were designed to avoid
rounding errors.

Looking at my data, I'm adding up the following three rows (value, display
string, and running total):

606351843, "$60,635.18", 606351843
116045591, "$11,604.56", 722397434
164854149, "$16,485.41", 887251583

So, 887251583 is my total, which displays as "$88,725.16". But if I add up
the values indicated by the display strings, I get 88,725.15.

How exactly is the approach the COM routines take to avoid rounding errors
helping here? I realize it won't perfect but this look really bad. Does
anyone have any suggestions?

Thanks.

Jonathan