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 manicure is a type of manicure that uses a coat of gel applied on the nails, with regular polish on top. The use of UV light to cure the gel allows the manicure to last longer. Shellac is a technology invented by Creative Nail Design (CND). It is similar to regular nail polish, but also uses UV light in between coats, which make it last as long as gel manicures.