From: Brian Candler <b.candler@...>
Date: 2010-07-12T19:15:36+09:00
Subject: Re: ruby float modulus operation.

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

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.
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