What do these preprocessors do and why they are needed ?

Question

#import,
#line,
#pragma region,
#pragma endregion,
#undef,
#using

Answer 1

King Sam

# pragma region to start a group of code and it should be followed by pragma endregion...

undef is used to nullify effect of define

using is used to have namespace into code

#import is similar to include... but import is limited to Microsoft only.. you can use import in visual c++, not c++ standalone.

Answer 2

and as for #line:

https://msdn.microsoft.com/en-us/library/b5w2czay.aspx