Answer 1

An instruction that tells to the preprocessor (the first part of the compiler) to do something. For example #include is a preprocessor directive, used to import headers.

Answer 2

Preprocessor directives are lines included in a program that begin with the character #, which make them different from a typical source code text. They are invoked by the compiler to process some programs before compilation. Preprocessor directives change the text of the source code and the result is a new source code without these directives.

Answer 3

hello

Answer 4

new group