# Ruby float modulus operation

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.

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…)

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.

On Mon, Jul 12, 2010 at 6:15 AM, Brian C. [email protected]
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:

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