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

A bitwise or with a negative number works JUST like a bitwise or with a positive number. The bits in one number are ored with the bits in the other number. How your processor represents negative numbers is a different matter. Most use something called "two's complement", which is essentially "invert the number and add 1".

So, if we have, for simplicity, 8 bit numbers:

15 is            00001111
Inverted we get  11110000
Add one          11110001

17 is            00010001

Ored together    11110001