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.
Gel nail polish is, hands down, the most popular service at nail salons right now. But many women may not be getting what they think they're getting. CND's Shellac is a brand of gel nail polish. It was the first to hit nail salons, offering a no-chip, super-shiny nail color lasting up to two weeks.