Keywords are words reserved for special purposes and must not be used as normal identifier names.  

If you use non-ANSI keywords in a program and you want the program to be ANSI compliant, always use the non-ANSI keyword versions that are prefixed with double underscores. Some keywords have a version prefixed with only one underscore; these keywords are provided to facilitate porting code developed with other compilers. For ANSI-specified keywords there is only one version.

and try are an exception to the discussion above. The keyword try is required to match the catch keyword in the C++ exception-handling mechanism. try cannot be substituted by __try. The keyword __try can only be used to match the __except or __finally keywords. See the discussions on C++ exception handling and C-based structured exceptions under Win32 for more information. Please see the Help table of contents for a complete categorical and alphabetical listing of keywords.