Lexical analysis

The input production defines the lexical structure of a C# source file. Each source file in a C# program must conform to this lexical grammar production. input :: input-section input-section :: input-section-partinput-sectioninput-section-partinput-section-part :: input-elements new-linepp-directiveinput-elements :: input-elementinput-elementsinput-elementinput-element :: whitespacecommenttoken
Five basic elements make up the lexical structure of a C# source file: Line terminators (9.3.1), white space (9.3.3), comments (9.3.2), tokens (9.4), and pre-processing directives (9.5). Of these basic elements, only tokens are significant in the syntactic grammar of a C# program (9.2.2).
The lexical processing of a C# source file consists of reducing the file into a sequence of tokens which becomes the input to the syntactic analysis. Line terminators, white space, and comments can serve to separate tokens, and pre-processing directives can cause sections of the source file to be skipped, but otherwise these lexical elements have no impact on the syntactic structure of a C# program.
When several lexical grammar productions match a sequence of characters in a source file, the lexical processing always forms the longest possible lexical element. [Example: For example, the character sequence // is processed as the beginning of a single-line comment because that lexical element is longer than a single / token. end example]