1.9489 - System.Math.Tru ncate(1.9489) = 0.9489000000000 0008

[Aamir Mahmood]

Try

[Aamir Mahmood]

Try it in immediate window
1.9489 - System.Math.Tru ncate(1.9489)

Result is
0.9489000000000 0008

Am I doing something wrong?

[Stephany Young]

What do expect the result to be?
"Aamir Mahmood" <aa**********@g mail.comwrote in message
news:%2******** **********@TK2M SFTNGP04.phx.gb l...

Try it in immediate window
1.9489 - System.Math.Tru ncate(1.9489)

Result is
0.9489000000000 0008

Am I doing something wrong?

[Jon Skeet [C# MVP]]

Aamir Mahmood <aa**********@g mail.comwrote:

Try it in immediate window
1.9489 - System.Math.Tru ncate(1.9489)

Result is
0.9489000000000 0008

Am I doing something wrong?

You're expecting decimal numbers to be exactly represented as doubles.

The literal 1.9489 ends up with a double of this exact value:
1.9489000000000 000767386154620 908200740814208 984375

The immediate window happens to print out lots of digits - a simple
call to Console.WriteLi ne doesn't. Which is the most appropriate action
really depends on what you're doing.

See http://pobox.com/~skeet/csharp/floatingpoint.html for more
information.

--
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

[=?ISO-8859-1?Q?Lasse_V=E5gs=E6ther_Karlsen?=]

Aamir Mahmood wrote:

Try

What is the question?

If you google for floating point errors, you should find tons of
information about this problem.

In short, a floating point value stored in a N-bit register is always
going to be an approximation of the real value. You will experience both
the case you see, that the value is slightly higher than what you expect
it to be, and the opposite, that it is slightly lower.

This is normal, can't be fixed, except for using a type with higher
precision and you must deal with it in your code.

As a quick-fix, try using the Decimal type.

--
Lasse Vågsæther Karlsen
mailto:la***@vk arlsen.no
http://presentationmode.blogspot.com/
PGP KeyID: 0xBCDEA2E3

[MC]

You've just bumped into a fundamental fact about computers -- They use binary arithmetic and do not have exact representations for some decimal numbers. For example, 0.5 is represented exactly but 0.1 is not.

This is exactly like the problem of representing 1/3 in decimal. 0.3 is close, 0.33 is closer, 0.333 is closer yet, but no finite number of 3's is enough.

The same thing happens with the binary digits when you are representing 0.1, or 0.9489. So the computer gives you an approximation.

The C# Decimal type actually represents numbers in base 10, the same way we do arithmetic with pencil and paper, but computation is slower that way.