There is not a matter of drivers development but a basic C/C++ mistake.
I have already advise what to do in post #2.

Isn't MSDN Library available for you?
MSDN Library: Compiler Warning C4018
Comparing a signed and unsigned number required the compiler to convert the signed value to unsigned.
This warning may be fixed if you cast one of the two types when testing signed and unsigned types.
Or you can to change types declared in your program in order to avoid signed/unsigned mismatch.

Need more advices?