Why is using a NON-decimal data type bad for money?

Question

tl;dr: What\'s wrong with my Cur (currency) structure?

tl;dr 2: Read the rest of the question please, before giving an

Answer 1

Usually monetary calculations require exact results, not just accurate results. float and double types cannot accurately represent the whole range of base 10 real numbers. For instance, 0.1 cannot be represented by a floating-point variable. What will be stored is the nearest representable value, which may be a number such as 0.0999999999999999996. Try it out for yourself by unit testing your struct - for example, attempt 2.00 - 1.10.