Oh wait. You are making a DLL and calling it inside LabVIEW?
My bad for misunderstanding haha.
Use this: Call Library Function Node
You can find detailed guides here:
http://www.ni.com/white-paper/3009/en/
http://zone.ni.com/reference/en-XX/help/371361J-01/lvexcodeconcepts/configuring_the_clf_node/
If you have a more specific question regarding them, let me know!