Meaning of bitwise and(&) of a positive and negative number?

Question

Can anyone help what n&-n means?? And what is the significance of it.

Answer 1

As @aestrivex has mentioned, it is a way of writing 1.Even i encountered this

for (int y = x; y > 0; y -= y & -y)

and it just means y=y-1 because
7&(-7) is x00000111 & x11111001 = x00000001 = 1