C# Preprocessor Directives

This section discusses the C# language's preprocessor directives:
#if
#else
#elif
#endif
#define
#undef
#warning
#error
#line
#region
#endregion
#pragma
#pragma warning
#pragma checksum
While the compiler does not have a separate preprocessor, the directives described in this section are processed as if there was one; these directives are used to aid in conditional compilation. Unlike C and C++ directives, you cannot use these directives to create macros.
A preprocessor directive must be the only instruction on a line.