Re: Rounding of the double

From:

"Tom Serface" <tom.nospam@camaswood.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Thu, 31 May 2007 19:54:52 -0700

Message-ID:

<BE2F9D50-9DF6-46A4-9989-4F9589BF676C@microsoft.com>

You could assign it back to a floating point (double):

double d = (double) result/100.0;

I think you'd get what you want on that.

Tom

"Alex" <alsim123@hotmail.com> wrote in message
news:1180634146.120833.45180@k79g2000hse.googlegroups.com...

Thanks, Tom,
It worked, but only half of the way :)

I've got 80.00000000000000000
But I need 0.80000000000000000

And of course I cannot get it, only
0.80000000000000004

And indeed, you are right, I have to calculate some percentage.
So instead of fractions (and correspondingly "double"s), I'll have to
change some code and work with percents (and correspondingly "int"s).

Funny, I've never thought that it's impossible to remove this garbage
from double.

Thanks,
Alex

On May 31, 12:37 pm, "Tom Serface" <tom.nos...@camaswood.com> wrote:

Hi Alex,

Depending on the size of the numbers you may want to try converting them
to
DWORDs and doing the division that way, then convert them back. For
example,

DWORD dw1 = (DWORD) f1 * 100;
DWORD dw2 = (DWORD) f2;

DWORD dw3 = dw1/dw2;

This works well when trying to figure out a percentage calculation for
exmaple.
double fResult = (double) dw3;

Tom

"Alex" <alsim...@hotmail.com> wrote in message

news:1180626964.583331.163830@p47g2000hsd.googlegroups.com...

I'd tried to use already Tom's link, I found it in some previous
posts. It doesn't work.
I'm calling RoundDouble( 0.80000000000000004, 4 )
At the end this function divides 80 by 100 and return of course
0.80000000000000004

So I think the problem is that "double" is also "float" in C++

It may sound stupid, but I'm going to use SQL Server to get the proper
result, it has type "numeric", if in SQL Server I divide numeric =
80.00, by numeric = 100.00 it returns correct result
0.80000000000000000
but if in SQL Server I divide float = 80.00, by float = 100.00 it
returns again result
0.80000000000000004

So SQL Server has numeric type and C++ doesn't. So I'll write some
SQL Server stored procedure, which will be using numeric data types.

Thanks,
Alex

On May 31, 11:36 am, MrAsm <m...@usa.com> wrote:

On 31 May 2007 08:10:16 -0700, Alex <alsim...@hotmail.com> wrote:

Everybody,
I'm lost
I have double d1 = 80.00
double d2 = 100.00

double result = d1/d2;

result = 0.80000000000000004 !!??

Why appears this "4" at the end!!??
It really makes difference for me.

Hi,

Floating point math is not an "exact" math (like e.g. integer math) in
computers.
When you do operations on floats (or doubles), you cannot expect an
"exact" result; there could be cancellation, rounding errors, etc.

In addition to Tom's link, you might consider also this:

http://cch.loria.fr/documentation/IEEE754/ACM/goldberg.pdf

MrAsm- Hide quoted text -

- Show quoted text -