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.
What Shellac is Not. Shellac is not lacquer. Both are high-performance, clear wood finishes originating in Asia, and both have names that derive from the same Sanskrit word (laksha), but lacquer is made from tree resin.