How to decide what to use - double or decimal? [duplicate]

Question

Possible Duplicate:
decimal vs double! - Which one should I use and when?

I'm using double type for price in my trading software. I've noticed that sometimes there are a odd errors. They occur if price contains 4 digits after "dot", like 2.1234.

When I sent from my program "2.1234" on the market order appears at the price of "2.1235".

I don't use decimal because I don't need "extreme" precision. I don't need to distinguish for examle "2.00000000003" from "2.00000000002". I need maximum 6 digits after a dot.

The question is - where is the line? When to use decimal?

Should I use decimal for any finansical operations? Even if I need just one digit after the dot? (1.1 1.2 etc.)

I know decimal is pretty slow so I would prefer to use double unless decimal is absolutely required.

Answer 1

Use decimal whenever you're dealing with quantities that you want to (and can) be represented exactly in base-10. That includes monetary values, because you want 2.1234 to be represented exactly as 2.1234.

Use double when you don't need an exact representation in base-10. This is usually good for handling measurements, because those are already approximations, not exact quantities.

Of course, if having or not an exact representation in base-10 is not important to you, other factors come into consideration, which may or may not matter depending on the specific situation:

• double has a larger range (it can handle very large and very small magnitudes);
• decimal has more precision (has more significant digits);
• you may need to use double to interact with some older APIs that are not aware of decimal;
• double is faster than decimal;
• decimal has a larger memory footprint;

Answer 2

When accuracy is needed and important, use decimal.

When accuracy is not that important, then you can use double.

In your case, you should be using decimal, as its financial matter.