Having the prototype available before the first use of the function allows the compiler to check that the correct number and type of arguments are used in the function call and that the returned value, if any, is being used reasonably. The function definition itself can act as an implicit function declaration.
While shellac is not usually the finish paint choice, it is often thought of as the best paint primer available. It has properties that oil and water based paints can't match, and provides a more dependable seal than most other primers are able to provide.
Apply it with a natural bristle brush or with a cotton rag. Shellac is available in most home centers as a liquid in a can. It also comes in solid form or in flakes that must be dissolved, and it has a shorter shelf life than other finishes. The liquid variety is the best option for the average homeowner.