Can anyone explain this strange behavior with signed floats in C#?

Question

Here is the example with comments:

class Program
{
    // first version of structure
    public struct D1
    {
        public double d;
        public int f         


        

Answer 1

It must be zero related, since changing the line

d.d = -0.0

to:

d.d = 0.0

results in the comparison being true...