Manual Chapter 3. Lexical Conventions Chapter 3. This chapter covers the C lexical conventions including comments and tokens. A token is a series of contiguous characters that the compiler treats as a unit. White space is ignored except as it serves to separate tokens.
Some white space is required to separate otherwise adjacent identifiers, keywords, and constants.
If the input stream has been parsed into tokens up to a given character, the next token is taken to include the longest string of characters that could possibly constitute a token. They do not indicate a comment when occurring within a string literal. Comments do not nest. The first character cannot be a digit. Uppercase and lowercase letters are distinct.