C# Multiplication error (double) [ Repost from C# forum ]

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When I do some thing simple like

double result = 3.1*4.1;

the result is 12.709999999999999

I would have expected 12.710000000000000

Is this normal for C#?

Posted 13-Dec-09 6:39am

cgl32000

Updated 13-Dec-09 7:03am

Richard MacCutchan

v2

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Richard MacCutchan · Answer 1 · 2009-12-13T07:06:00

Solution 1

This is normal, floating point numbers cannot always depict an accurate representation of a value. If you want to display the number rounded then the ToString() method offers that capability.

Posted 13-Dec-09 7:06am

Richard MacCutchan

Julian Nicholls · Answer 2 · 2009-12-13T08:26:00

There is a classic text, What Every Computer Scientist Should Know About Floating-Point Arithmetic[^] by David Goldberg that should help you understand what's happening here. It's not specific to C#, but rather the IEEE 754 standard for floating-point numbers that C# uses.

Suffice to say, it is normal, merely a common rounding error, similar to what you might have encountered in grade school when trying to represent the result of an expression such as 10 / 3 in decimal form...

AWriter · Answer 3 · 2010-08-23T04:27:00

Solution 3

I had the same problem. The only solution I found is to convert the values to decimals, multiply them and after that convert to Double. That's expensive, but if no other solution is available, is acceptable.

Posted 23-Aug-10 4:27am

AWriter

Comments

Toli Cuturicu 23-Aug-10 10:43am

Reason for my vote of 2
Non-problem, non-solution!