#elif (C# Reference)
#elif lets you create a compound conditional directive. The #elif expression will be evaluated if neither the preceding #if (C# Reference) nor any preceding, optional, #elif directive expressions evaluate to true. If a #elif expression evaluates to true, the compiler evaluates all the code between the #elif and the next conditional directive. For example:
#define VC7
//...
#if debug
Console.Writeline("Debug build");
#elif VC7
Console.Writeline("Visual Studio 7");
#endif
You can use the operators == (equality), != (inequality), && (and), and || (or), to evaluate multiple symbols. You can also group symbols and operators with parentheses.
Remarks
#elif is equivalent to using:
#else
#if
Using #elif is simpler, because each #if requires a #endif (C# Reference), whereas a #elif can be used without a matching #endif.
See #if (C# Reference) for an example of how to use #elif.