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.
Shellac is a wood finishing product made by dissolving dried resin in denatured alcohol. Shellac was used heavily for finishing furniture during the 19th and early 20th centuries, and it is still available for use today. The product is popular due to its ease of application, low odor, and all-natural origin.