So you are expecting h to be a non-scalar.
if (Nh < 0 && (Nh > h + 2*r))
You add the non-scalar h to something and compare it to the scalar Nh, producing a non-scalar result on the right hand side of the && . However, the && operator can only be used when both sides are scalars.
Changing to & is not the correct solution. The correct solution is to stop using single-letter variable names that differ only in upper versus lower case, because it is too easy to get the wrong variable name. You do not want h there, you want H .
In your other question, H and 2*r were both positive, and Nh > some_positive_value cannot be simultaneously true with Nh < zero.