Ruby Integer / Fixnum weirdness

Question

I'm trying to write a function that pulls the lowest order number out of an integer. Eg:

> 24689.lowest_order
=> 9

Thus far I have:

class Integer
  def lowest_order
    Integer (self / 10.0 - self / 10) * 10
  end
end

And it works....sometimes:

irb(main):002:0> n = 235
=> 235
irb(main):007:0> n.class
=> Fixnum
irb(main):004:0> n/10.0
=> 23.5
irb(main):005:0> n/10
=> 23
irb(main):003:0> n.lowest_order
=> 5
irb(main):008:0> (n/10.0 - n/10)*10
=> 5.0

while other times it fails (no code change between examples):

irb(main):010:0> n = 232
=> 232
irb(main):021:0> n.class
=> Fixnum
irb(main):009:0> n.lowest_order
=> 1
irb(main):011:0> n/10.0
=> 23.2
irb(main):012:0> n/10
=> 23
irb(main):013:0> n/10.0 - n/10
=> 0.199999999999999
irb(main):022:0> n = Integer 232
=> 232
irb(main):023:0> n/10.0 - n/10
=> 0.199999999999999

Whats the deal? I'd rather not have to filter integer through String just to fetch the most minor part of the number.

Thanks!

Answer 1

Is there a reason you can't just do n % 10 or n.modulo 10 (see documentation)?

To answer the "why doesn't this work?" portion of your question, the answer is that floating point arithmetic doesn't always behave as you'd expect it to.