I am new to LabWindows/CVI. Can anyone please explain, what is the major difference between LabWindows/CVI and C#.
As far as I can tell, they're completely different.
C# is a language, developed primarily by Microsoft, usually targeting the .NET framework.
LabWindows/CVI is (according to the documentation):
LabWindows/CVI is a proven ANSI C development environment for test and measurement that increases the productivity of engineers and scientists.
In other words, it's an IDE for a different language (C), along with tools and libraries particularly suitable for engineers and scientists.