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.NET Forum / .NET Framework / New Users / March 2006Decimal/Single/...: which Numeric-type to use?
Hi, I'm having some troubles with my numeric-types in my VB.NET 2005 application, together with a SQL Server 2000. - I first used Single in my application, and Decimal in my database. But a Single with value 4.475 was converted to a Decimal with value 4.4749999999999996D. So after inserting and selecting it from the database I got another value than the original! - So I used also the Decimal in my application, but now all my numbers are formatted with all the decimals: when my value is "1", it shows "1.0000". A single value roudns it nicely to 1, but the decimal value shows the whole decimal part, even when it isn't needed. What I need is: the users should only see the decimal part when needed, AND my values have to be the same (no 4.475 to 4.474999999999 changements). This seems such a simple and basic need, but I just keep having troubles with it :-( What should I do/use? Another numeric datatype in my application? Another datatype in my Database?? Any help/hints/links/information would be really appreciated! Thansk a lot in advance, Pieter er, it depends are the calculations that you are performing financial style calcs where precision is everything? if so use Decimal. or are they scientific calcs where you have a wide range of numbers that need ot be accurate to a a given nummber of digits? (eg calculation of stresses in an engineering project) in this case use Double. I wouldnt use Single unless... it is a leagacy app being converted or you have REALLY big arrays and are tight on memory dont worry about the formatting, that is trivial comapred with getting the data right, you can sort it out later. hth guy > Hi, > [quoted text clipped - 25 lines] > > Pieter Precision is indeed everything. Most of the time it are prices, weights, heights etc. So it has to be exact. And I do worry about the formatting, because when I show the decimal value in a Textbox, it shows all the zeros after the decimal, and I don't want it to do it. Especially in some cases where it contains most of the time whole numbers (1, 2, 3, ...) and rarely 1.001 etc. So I don't want the user to be seeing the whole time 1.0000, 2.0000, 3.0000, etc. Basicly: I need exact precision, but without the zeros at the end. How should I do that? there isn't a Format-property on the textbox... > er, it depends > are the calculations that you are performing financial style calcs where [quoted text clipped - 12 lines] > > guy look at the overloads of Decimal.ToString this one may help... (it is the online version of Help) http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlr fsystemdecimalclasstostringtopic3.asp hth guy > Precision is indeed everything. Most of the time it are prices, weights, > heights etc. So it has to be exact. [quoted text clipped - 25 lines] > > > > guy Thanks, but this means that I have to change manually every numeric property of my objects to a string? And that I can't anymore DataBind my controls directly to the propertys of my objects? It seems a little bit a werid solution for such a problem. Why does a Single threats the trailing zeros right (cuts them off) but doesn't have ap recision, and does a decimal the opposite? Isn't there somehow a datatype that combines the two? I can't be the only one with this problem???? > look at the overloads of Decimal.ToString > [quoted text clipped - 6 lines] > > guy another thing to consider... in one project i have developed, i built a set of structuers - Distance, Area, volume, Weight etc. which wrapped a double (you could equally well use a decimal) with appropriate overloads and formatting. It sounds a lot of work but more than paid for itself in functionality and ensuring correct variable usage. > Thanks, but this means that I have to change manually every numeric property > of my objects to a string? And that I can't anymore DataBind my controls [quoted text clipped - 16 lines] > > > > guy Ok, thanks for the help on this issue. So if I am right I should define my propertys like this: Public Property FraisEmballageOriginal() As Decimal Get Return m_decFraisEmballageOriginal.ToString("0.##") End Get > another thing to consider... > in one project i have developed, i built a set of structuers - Distance, [quoted text clipped - 5 lines] > variable > usage. Pieter, the key is to separate what you display to the operator and the actual value in your classes. use the data type of your choice in the class, but build a formatting method to present it to the operator that does not interfere with applicationss internals > Ok, thanks for the help on this issue. > So if I am right I should define my propertys like this: [quoted text clipped - 4 lines] > > Return m_decFraisEmballageOriginal.ToString("0.##") *** this wont work, the data type is decimal so you cant return a string *** > End Get > [quoted text clipped - 7 lines] > > variable > > usage. Pieter, I have the idea that you do not use precise but rounded decimal values. Be aware that it uses Banking roundings as default. In version 2005 you can as well use other roundings (as standard is used in the Benelux by instance). I could not find the information on MSDN, so have a look for yourself. Cor > Precision is indeed everything. Most of the time it are prices, weights, > heights etc. So it has to be exact. [quoted text clipped - 26 lines] >> >> guy I did some test: I used single in my application, and Float, Real, Decimal and Numeric in my database. The combination Single-float/Real works great, and give mle the exact results that I wanted. Should I use this? Or is there some problem that I'm not seeing? It doesn't round the precision, and it cuts off the trailing zeroes... > Hi, > [quoted text clipped - 26 lines] > > Pieter > Hi, > > I'm having some troubles with my numeric-types in my VB.NET 2005 > application, together with a SQL Server 2000. > > - I first used Single in my application, and Decimal in my database. Use the same type to process and store floating numbers, otherwise you will multiply loss of precision. Single numbers are "float", and uses base 2, that is it can represent multiples of halves without precision loss (upto the precision limits). Decimal is base10 and can represent decimal-numbers without loss (upto the precision limit). > Single with value 4.475 was converted to a Decimal with value > 4.4749999999999996D. So after inserting and selecting it from the database I > got another value than the original! Actually what happened is that Signgle (float) cannot represent 4.475 without loss, it becomes a bit-pattern which represents 4.4749999999999996. So the conversion to decimal does not loose precision, the use of float to represent base10 numbers does. If you format 4.475 as: (4.475).ToString("##.###") you *will* get 4.475, since the presentation will do rounding. > - So I used also the Decimal in my application, but now all my numbers are > formatted with all the decimals: when my value is "1", it shows "1.0000". A > single value roudns it nicely to 1, but the decimal value shows the whole > decimal part, even when it isn't needed. You should look into how the numbers are presented to the user. Have a look at ToString(format) and NumberFormatInfo. > What I need is: the users should only see the decimal part when needed, AND > my values have to be the same (no 4.475 to 4.474999999999 changements). That can be done with Decimal, which can represent base10 without loss of precision. beware you you may stil inadvertently generate numbers which does *not* have representation without loss in base 10, for example by division. > This seems such a simple and basic need, but I just keep having troubles > with it :-( floating-point precision numbers are not "reals" as in math, they do not have infinite precision, that's the problem here. > What should I do/use? Another numeric datatype in my application? Another > datatype in my Database?? Decimal all-round if your *really* need the precision (not just as 4.475), otherwise just use the same in app and databse. And learn to format the numbers presented to the users, have a look at ToString with formatting arguments and the string-conversions in string.Format. Whatever you do, dont start using strings to represent numbers in your calculations and interface, that won't help you.  SignatureHelge Jensen mailto:helge.jensen@slog.dk sip:helge.jensen@slog.dk -=> Sebastian cover-music: http://ungdomshus.nu <=- Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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