# Ruby float modulus operation **URL:** \ **Category:** Ruby\ **Created:** [July 12, 2010, 10:20am UTC](https://www.ruby-forum.com/t/ruby-float-modulus-operation/191414 "2010-07-12T10:20:35Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Karthick\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a88e57/32.png) [@Karthick\_S](https://www.ruby-forum.com/u/Karthick_S)\ **Post date:** [July 12, 2010, 10:20am UTC](https://www.ruby-forum.com/t/ruby-float-modulus-operation/191414/1 "2010-07-12T10:20:35Z")
Hi, I am new to ruby and found this while experimenting with ruby. irb(main):010:0\> 5.1%0.5 =\> 0.0999999999999996 irb(main):011:0\> Is this similar to the float related operations that MS Excel has? - Karthick S. ---
**Author:** ![Karthick\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a88e57/32.png) [@Karthick\_S](https://www.ruby-forum.com/u/Karthick_S)\ **Post date:** [July 12, 2010, 12:15pm UTC](https://www.ruby-forum.com/t/ruby-float-modulus-operation/191414/2 "2010-07-12T12:15:34Z")
Karthick S. wrote: > I am new to ruby and found this while experimenting with ruby. > > irb(main):010:0\> 5.1%0.5 > =\> 0.0999999999999996 Ruby is no different to any other language which uses binary floating point arithmetic: $ perl -e ‘print 5.1 - 10\*0.5, “\n”’ 0.0999999999999996 The problem is that 1/10 does not have an exact representation in binary floating point, in the same way that 1/3 does not have an exact representation in decimal floating point (0.33333…) To learn more see [http://docs.sun.com/source/806-3568/ncg\_goldberg.html](http://docs.sun.com/source/806-3568/ncg_goldberg.html) For some applications, you might use the Rational or BigDecimal classes instead. If dealing with currency, you can work in Integers for cents/pence etc. Or maybe you just want to use fewer significant digits when printing: > > v = 5.1 % 0.5 > > =\> 0.0999999999999996 > > “%.8f” % v > > =\> “0.10000000” although you’re still likely to be tripped up by this: > > v == 0.1 > > =\> false HTH, Brian. ---
**Author:** ![Karthick\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/a88e57/32.png) [@Karthick\_S](https://www.ruby-forum.com/u/Karthick_S)\ **Post date:** [July 12, 2010, 4:00pm UTC](https://www.ruby-forum.com/t/ruby-float-modulus-operation/191414/3 "2010-07-12T16:00:44Z")
On Mon, Jul 12, 2010 at 6:15 AM, Brian C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Karthick S. wrote: > > > I am new to ruby and found this while experimenting with ruby. > > > > irb(main):010:0\> 5.1%0.5 > > =\> 0.0999999999999996 > > Ruby is no different to any other language which uses binary floating > point arithmetic It isn’t relevant to the OPs example, but not all languages produce the results for modulo when presented with negative arguments: > **[Modulo | Common pitfalls](https://en.wikipedia.org/wiki/Modulo_operation#Common_pitfalls)** > > When the result of a modulo operation has the sign of the dividend (truncated definition), it can lead to surprising mistakes. > For example, to test if an integer is odd, one might be inclined to test if the remainder by 2 is equal to 1: > But in a language where modulo has the sign of the dividend, that is incorrect, because when n (the dividend) is negative and odd, n mod 2 returns −1, and the function returns false. > One correct alternative is to test that the remainder is not 0 (because remain... Ruby, Perl, and MS Excel all return a result with the sign of the divisor, while Java returns a result with the sign of the dividend. – Rick DeNatale Blog: [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) Github: [rubyredrick (Rick DeNatale) · GitHub](http://github.com/rubyredrick) Twitter: @RickDeNatale WWR: [http://www.workingwithrails.com/person/9021-rick-denatale](http://www.workingwithrails.com/person/9021-rick-denatale) LinkedIn: [http://www.linkedin.com/in/rickdenatale](http://www.linkedin.com/in/rickdenatale)