decimal vs double! - Which one should I use and wh

Question

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• When should I use double instead of decimal? 12 answers

I keep seeing people using doubles in C#. I know I read somewhere that doubles sometimes lose precision. My question is when should a use a double and when should I use a decimal type? Which type is suitable for money computations? (ie. greater than $100 million)

Answer 1

Definitely use integer types for your money computations. This cannot be emphasized enough, since at first glance it might seem that a floating point type is adequate.

Here an example in python code:

>>> amount = float(100.00) # one hundred dollars
>>> print amount
100.0
>>> new_amount = amount + 1
>>> print new_amount
101.0
>>> print new_amount - amount
>>> 1.0

looks pretty normal.

Now try this again with 10^20 Zimbabwe dollars

>>> amount = float(1e20)
>>> print amount
1e+20
>>> new_amount = amount + 1
>>> print new_amount
1e+20
>>> print new_amount-amount
0.0

As you can see, the dollar disappeared.

If you use the integer type, it works fine:

>>> amount = int(1e20)
>>> print amount
100000000000000000000
>>> new_amount = amount + 1
>>> print new_amount
100000000000000000001
>>> print new_amount - amount
1