You didn't say what development environment you're using, so I'm assuming Visual Studio. It sounds like you created a Win32 app (as opposed to an MFC app). This has a "WinMain" function. The prototype for WinMain is geared towards it being called by the OS when you run the executable. You could just add the __declspec(export) directive in front of the return type, but you also need to change some build functions in Visual Studio to get a DLL. You probably also don't need all the arguments that WinMain uses. You're probably better off by starting with a new DLL project in order to get the framework for a DLL, and then copy and past the function code. That's what I would do.
I would also
strongly suggest that you crack open the "Using External Code in LabVIEW" manual that gets installed when you installed LabVIEW. It's in the "manuals" directory, filename of "lvexcode.pdf".
