Why does this decimal division not give an exact result?

[Elroy Flynn]

Decimal a = 42.485M;
Decimal b = 48M;
Decimal c = a / b;
Console.WriteLi ne(c.ToString() );

gives the result 0.8851041666666 666666666666667

The correct, exact answer is .885.

I know that floating point types cannot represent some values
precisely, but the decimal type (which is a base 10 FP type) CAN
represent these three values (the dividend, divisor, and quotient)
exactly.

Furthermore, doc states that "The result of an operation on values of
type decimal is that which would result from calculating an exact
result (preserving scale, as defined for each operator) and then
rounding to fit the representation. "

Could someone explain this unexpected result?

[John Heitmuller.]

Re: Why does this decimal division not give an exact result?

Hmmm... I just ran this on Excel and got a result of
0.8851041666666 67. So, I calculated it by hand and got the same
result as Excel. Am I not understanding the setup of you problem? I
don't think the .885 is the propper result.

John

[Jeff Johnson]

Re: Why does this decimal division not give an exact result?

"Elroy Flynn" <leotohill@gmai l.comwrote in message
news:2edcadcc-7e3b-4301-81eb-7b209c87923f@t4 2g2000hsg.googl egroups.com...

Decimal a = 42.485M;
Decimal b = 48M;
Decimal c = a / b;
Console.WriteLi ne(c.ToString() );
>
gives the result 0.8851041666666 666666666666667
>
The correct, exact answer is .885.

Methinks you were using the numeric keypad and accidentally hit 5 when you
hit 8, because 42.48 / 48 = .885, not 42.485.

[Peter Duniho]

Re: Why does this decimal division not give an exact result?

On Fri, 17 Oct 2008 11:15:40 -0700, Elroy Flynn <leotohill@gmai l.com>
wrote:

Decimal a = 42.485M;
Decimal b = 48M;
Decimal c = a / b;
Console.WriteLi ne(c.ToString() );
>
gives the result 0.8851041666666 666666666666667
>
The correct, exact answer is .885.
>
I know that floating point types cannot represent some values
precisely, but the decimal type (which is a base 10 FP type) CAN
represent these three values (the dividend, divisor, and quotient)
exactly.

Why do you say that?

Furthermore, doc states that "The result of an operation on values of
type decimal is that which would result from calculating an exact
result (preserving scale, as defined for each operator) and then
rounding to fit the representation. "
>
Could someone explain this unexpected result?

Look at this code:

decimal a = 2;
decimal b = 3;
decimal c = a / b;

Console.WriteLi ne(c.ToString() );

What should that print out?

Pete

[Jon Skeet [C# MVP]]

Re: Why does this decimal division not give an exact result?

Elroy Flynn <leotohill@gmai l.comwrote:

Decimal a = 42.485M;
Decimal b = 48M;
Decimal c = a / b;
Console.WriteLi ne(c.ToString() );
>
gives the result 0.8851041666666 666666666666667
>
The correct, exact answer is .885.

It's really not. 0.885 * 48 = 42.48.

I know that floating point types cannot represent some values
precisely, but the decimal type (which is a base 10 FP type) CAN
represent these three values (the dividend, divisor, and quotient)
exactly.
>
Furthermore, doc states that "The result of an operation on values of
type decimal is that which would result from calculating an exact
result (preserving scale, as defined for each operator) and then
rounding to fit the representation. "
>
Could someone explain this unexpected result?

Your expectations are flawed :) Make a = 42.48M and you'll get your
expected result.

--
Jon Skeet - <skeet@pobox.co m>
Web site: http://www.pobox.com/~skeet
Blog: http://www.msmvps.com/jon.skeet
C# in Depth: http://csharpindepth.com

[Elroy Flynn]

Re: Why does this decimal division not give an exact result?

On Oct 17, 3:21 pm, Jon Skeet [C# MVP] <sk...@pobox.co mwrote:

Elroy Flynn <leotoh...@gmai l.comwrote:

Decimal a = 42.485M;
Decimal b = 48M;
Decimal c = a / b;
Console.WriteLi ne(c.ToString() );

>

gives the result 0.8851041666666 666666666666667

>

The correct, exact answer is .885.

>
It's really not. 0.885 * 48 = 42.48.
>

I know that floating point types cannot represent some values
precisely, but the decimal type (which is a base 10 FP type) CAN
represent these three values (the dividend, divisor, and quotient)
exactly.

>

Furthermore, doc states that "The result of an operation on values of
type decimal is that which would result from calculating an exact
result (preserving scale, as defined for each operator) and then
rounding to fit the representation. "

>

Could someone explain this unexpected result?

>
Your expectations are flawed :) Make a = 42.48M and you'll get your
expected result.
>
--
Jon Skeet - <sk...@pobox.co m>
Web site:http://www.pobox.com/~skeet 
Blog:http://www.msmvps.com/jon.skeet
C# in Depth:http://csharpindepth.com

where's the "delete from web" command?

[=?ISO-8859-1?Q?Arne_Vajh=F8j?=]

Re: Why does this decimal division not give an exact result?

Michael B. Trausch wrote:

On Fri, 17 Oct 2008 13:56:44 -0700 (PDT)
Elroy Flynn <leotohill@gmai l.comwrote:

>where's the "delete from web" command?

>
This is a newsgroup. You cannot delete your post once you have sent
it, because most servers on Usenet do not honor the commands that used
to be used for that since they've been abused in the past.
>
As far as Google Groups, you'll have to go through the same process
that anyone that wants to have their messages pulled from their
archives has to do: Find the form if they still have it and request
that the message(s) be removed by their Message ID. You will also have
to prove that you own the email address associated with the Message ID.

I don't think it was meant that literally.

Arne

[Peter Morris]

Re: Why does this decimal division not give an exact result?

Are you posting in HTML format or something? To me your posts are empty but
have two attachments...

01: ATT0096.txt
02: signature.asc



--
Pete
====

http://mrpmorris.blogspot.com

http://www.capableobjects.com

[Family Tree Mike]

[OT] Strange Postings

As Peter Morris indicated with your other post, something strange is
happening. You actual text is showing as an attachment to a blank post.
The post on this part of the thread that Arne V. responded to did not come
through at all. I'm using Windows Mail to view the group.

Both appear fine at the microsoft discussion groups page though, but it's
strange...

"Michael B. Trausch" <mike@trausch.u swrote in message
news:2008101723 2431.338ecb01@z est...

[=?UTF-8?B?R8O2cmFuIEFuZGVyc3Nvbg==?=]

Re: [OT] Strange Postings

Family Tree Mike wrote:

As Peter Morris indicated with your other post, something strange is
happening. You actual text is showing as an attachment to a blank post.
The post on this part of the thread that Arne V. responded to did not
come through at all. I'm using Windows Mail to view the group.
>
Both appear fine at the microsoft discussion groups page though, but
it's strange...

I use Thunderbird to view the newsgroups, and there the posts show up
just as usual.

--
Göran Andersson
_____

http://www.guffa.com