mbailey/gist:1531950

Created December 29, 2011 04:43

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Should I not use ruby to add dollar values?

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gistfile1.txt

	mbailey@oasis:~ $ irb
	1.9.2p290 :001 > 120.82+15.96+135.50
	=> 272.28
	1.9.2p290 :002 > 120.82+15.96+135.51
	=> 272.28999999999996

mipearson commented Dec 29, 2011

ruby-1.9.3-p0 :001 > 120.82+15.96+135.51 => 272.28999999999996 ruby-1.9.3-p0 :002 > sprintf("%0.2f", 120.82+15.96+135.51) => "272.29"

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mbailey commented Dec 29, 2011

Thanks Michael! I'm surprised I've not noticed that before. :-)

mipearson commented Dec 29, 2011

NP! Also interesting: http://en.wikipedia.org/wiki/0.999...

seancaffery commented Dec 30, 2011

I think that you should use two fields; a dollar and a cent amount.
I have have to change the way that I dealt with money values recently due to similar issues in the database.

mipearson commented Dec 30, 2011

@seancaffery: I disagree. Use a dedicated fixed-point decimal class or represent all monetary amounts internally as their smallest possible fraction. Eg, represent $100.00 as 10000, or two dollars fifty as $2.50.

If you get into a situation where you need to divide the amount, clever use of floor and ceil will ensure you have no leftovers.

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