How does C++ do bitwise “or” operations on negative numbers?

Question

When I give to a variable such value: e = 17|-15; , I get -15 as an answer after compiling.I can\'t understand what arithmetic c++ uses. How does it perform a

Answer 1

   17 = b00010001
  -15 = b11110001 <--- 2s complement
| -15 = b11110001