Precision of Double->Wrong calculations

[Th.Krebs]

Hello all,

we just got a little problem with the correctness of VB.Net.

What would u expect as the result of
4.35 * 100.0

435.0 u think ?

well, VB.Net tells us, that the result of this
calculation will be:

4.35*100.0 434.99999999999994 Double

Who is right here, and how can we avoid these kind of miscalculations.
Using Decimal instead of Double?
Thanks for reading and answering this post.
Thomas

 

[Herfried K. Wagner [MVP]]

What would u expect as the result of
4.35 * 100.0

435.0 u think ?

well, VB.Net tells us, that the result of this
calculation will be:

4.35*100.0 434.99999999999994 Double

Who is right here, and how can we avoid these kind of miscalculations.
Using Decimal instead of Double?

For the reasons, see:

<URL:http://research.microsoft.com/~hollasch/cgindex/coding/ieeefloat.html>
<URL:http://www.math.grin.edu/~stone/courses/fundamentals/IEEE-reals.html>
<URL:http://support.microsoft.com/?scid=kb;[LN];42980>

MSDN on 'Decimal':

---
The 'Decimal' value type represents 'Decimal' numbers ranging from positive
79,228,162,514,264,337,593,543,950,335 to negative
79,228,162,514,264,337,593,543,950,335. The 'Decimal' value type is
appropriate for financial calculations requiring large numbers of
significant integral and fractional digits and no round-off errors.

 

[Jay B. Harlow [MVP - Outlook]]

Thomas,
I would expect something close to 434.99999999999994...

In addition to the links that Herfried gave see:

http://www.yoda.arachsys.com/csharp/floatingpoint.html
http://www.yoda.arachsys.com/csharp/decimal.html

Hope this helps
Jay