In .net, how do I choose between a Decimal and a Double
.net, floating-point
Solution
I usually think about natural vs artificial quantities.
Natural quantities are things like weight, height and time. These will never be measured absolutely accurately, and there's rarely any idea of absolutely exact arithmetic on it: you shouldn't generally be adding up heights and then making sure that the result is exactly as expected. Use `double` for this sort of quantity. Doubles have a huge range, but limited precision; they're also extremely fast.
The dominant artificial quantity is money. There is such a thing as "exactly $10.52", and if you add 48 cents to it you expect to have exactly $11. Use `decimal` for this sort of quantity. Justification: given that it's artificial to start with, the numbers involved are artificial too, designed to meet human needs - which means they're naturally expressed in base 10. Make the storage representation match the human representation. `decimal` doesn't have the range of `double`, but most artificial quantities don't need that extra range either. It's also slower than `double`, but I'd personally have a bank account which gave me the right answer slowly than a wrong answer quickly :)
For a bit more information, I have articles on .NET binary floating point types and the .NET decimal type. (Note that `decimal` is a floating point type too - but the "point" in question is a decimal point, not a binary point.)
Problem
We were discussing this the other day at work and I wish there was a Stackoverflow question I would point people at so here goes.) - What is the difference between a `Double` and a `Decimal`? - When (in what cases) should you always use a `Double`? - When (in what cases) should you always use a `Decimal`? - What’s the driving factors to consider in cases that don’t fall into one of the two camps above? There are a lot of questions that overlap this question, but they tend to be asking what someone should do in a given case, not how to decide in the general case.