Will you ever have to deal with negative numbers? If so, you need to test
that case as well.

helen

-----Original Message-----
From: Discussion of advanced .NET topics.
[mailto:ADVANCED-DOTNET@DISC...] On Behalf Of Eddie Lascu
Sent: Monday, August 25, 2008 10:24 AM
To: ADVANCED-DOTNET@DISC...
Subject: Re: [ADVANCED-DOTNET] Converting doubles into integers without
rounding errors

Hi John,

I just tested this and I am happy with the return as I got what I expected
in each case:

Console.WriteLine(Math.Round((123.454 * 100.0) - 0.5));  // expect 12345
Console.WriteLine(Math.Round((123.455 * 100.0) - 0.5));  // expect 12345
Console.WriteLine(Math.Round((123.456 * 100.0) - 0.5));  // expect 12345

Console.WriteLine(Math.Round((123.464 * 100.0) - 0.5));  // expect 12346
Console.WriteLine(Math.Round((123.465 * 100.0) - 0.5));  // expect 12346
Console.WriteLine(Math.Round((123.466 * 100.0) - 0.5));  // expect 12346

The problem though is that I can never be sure that amount 123.45 will not
be stored as 123.4499999. According to the above approach, this will be
converted to 12344 which is not what I want.


-----Original Message-----
From: Discussion of advanced .NET topics.
[mailto:ADVANCED-DOTNET@DISC...]On Behalf Of John Warner
Sent: Monday, August 25, 2008 1:11 PM
To: ADVANCED-DOTNET@DISC...
Subject: Re: [ADVANCED-DOTNET] Converting doubles into integers without
rounding errors
Importance: Low


What result do you want from the examples you borrow from MSDN? Again have
you considered 1000.0 instead of 100.0 and do your own round?

John Warner




> -----Original Message-----
> From: Discussion of advanced .NET topics.
> [mailto:ADVANCED-DOTNET@DISC...] On Behalf Of Eddie Lascu
> Sent: Monday, August 25, 2008 1:04 PM
> To: ADVANCED-DOTNET@DISC...
> Subject: Re: [ADVANCED-DOTNET] Converting doubles into
> integers without rounding errors
>
>
> According to MSDN, Math.Round will return the following:
>
> Math.Round(4.4); //Returns 4.0.
> Math.Round(4.5); //Returns 4.0.
> Math.Round(4.6); //Returns 5.0.
>
> So, in my case doing Math.Round(objMyObject.Amount * 100.0)
> will not do the trick always. For example:
>
> Math.Round(123.454 * 100.0); // returns 12345
> Math.Round(123.455 * 100.0); // returns 12345
> Math.Round(123.456 * 100.0); // returns 12346
>
> So I suppose I need to execute this:
>
> Math.Round((objMyObject.Amount * 100.0) - 0.5) to be sure
> that I get what I want.
>
> Am I missing something?
>
>
>
> -----Original Message-----
> From: Discussion of advanced .NET topics.
> [mailto:ADVANCED-DOTNET@DISC...]On Behalf Of Peter Ritchie
> Sent: Monday, August 25, 2008 12:48 PM
> To: ADVANCED-DOTNET@DISC...
> Subject: Re: [ADVANCED-DOTNET] Converting doubles into
> integers without rounding errors
>
>
> As John has alluded to, what you're seeing is a difference in
> rounding between formatting a double value as text and
> multiplying by 100 and dropping the decimals.
>
> If you have specific rounding logic, perform it before you
> convert to int.  If you want the same value that you'd see as
> formatted text, convert to text first.
>
> I would recommend something like this:
>
> double tempAmount = objMyObject.Amount * 100.0;
> uint nIntAmount = Math.Round(tempAmount);
>
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