What do the hash signs in #if, #else, #end if mean?

Question

I\'m writing code to check if a file is available to be checked out of SharePoint and, if it isn\'t, alert the user and tell them that the file is in use by someone else and

Answer 1

The hash indicates that it's a directive. Used for literally including or excluding code from compilation.

http://msdn.microsoft.com/en-us/library/7ah135z7.aspx

whoops that's for vb.net isn't it. Same concept I think.