It depends on the requirements of your app and what programming language you use. Sometimes you can get away with using a fixed precision that you can assume everywhere, but most common programming languages will have some implementation of a decimal type with variable precision if needed, so you won't need to implement it on your own outside of university exercises.

No exponent, or at least a common fixed exponent. The technique is called "fixed point" as opposed to "floating point". The rationale is always to have a known level of precision.