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Asked: 2026-05-28T02:39:29+00:00

According to the MSDN article found at http://msdn.microsoft.com/en-us/library/wyk4d9cy.aspx the floating-point value .1 has no

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According to the MSDN article found at http://msdn.microsoft.com/en-us/library/wyk4d9cy.aspx the floating-point value .1 has no finite binary representation, the first call to the Round(Double) method with a value of 11.5 returns 11 instead of 12.
I can’t clearly understand, why does it happen?

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1 Answer

  1. Editorial Team

    The first call isn’t really using 11.5. It’s using a value slightly less than 11.5 due to an accumulation of errors from adding 0.1 repeatedly. Here’s the output if you use my DoubleConverter.ToExactString to show the exact values being passed in:

    11.0999999999999996447286321199499070644378662109375 --> 11
11.199999999999999289457264239899814128875732421875 --> 11
11.2999999999999989341858963598497211933135986328125 --> 11
11.39999999999999857891452847979962825775146484375 --> 11
11.4999999999999982236431605997495353221893310546875 --> 11
11.599999999999997868371792719699442386627197265625 --> 12

11.5 --> 12

    At that point, all the results make sense.

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