How does "|" operator evaluate two integers?

Question

I have something that I haven't yet wrapped my head around yet; how does the | operand evaluate numbers?

#include<iostream>

int main()
{
    int x, y, z;
    x = 2;
    y = 4;

    z = x | y;
}

Why does z get assigned 6 in this case; how does this work?

*bitwise*. Concepts required: Bits, binary representation, logical operations. Nice to have: Boolean algebra. — Eugene Sh., May 08 '18 at 21:14
Sounds like you could use a [good C++ book](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) — NathanOliver, May 08 '18 at 21:16

Achal · Answer 1 · 2018-05-08T21:24:10.560

The operator | is called bitwise OR. and its truth table is

A  B   A|B ( operate on bits)
----------
0  0    0
0  1    1
1  0    1
1  1    1

In your case x=2 and y=4. By assuming both x and y are 32 bit integer, while doing x | y just follow above table. It looks like

    MSB                                        LSB <-- little enidian
x = 0000 0000 | 0000 0000 | 0000 0000 | 0000 0010
                                                |
y = 0000 0000 | 0000 0000 | 0000 0000 | 0000 0100                                           
-------------------------------------------------
z = 0000 0000 | 0000 0000 | 0000 0000 | 0000 0110 => 6
--------------------------------------------------

wally · Answer 2 · 2018-05-08T21:30:29.830

2

| means bitwise OR. The OR is applied to each bit. (4 becomes 100, 2 becomes 10):

   4    0100
OR 2    0010
------------
== 6    0110
------------

Together the bitwise OR produces 110 which is 6.

Please note that this is not an addition and there is no carry of the bits like with the + operator.

So for example:

   6    0110
 + 2    0010
------------
== 8    1000
------------

but:

   6    0110
OR 2    0010
------------
== 6    0110
------------

edited May 08 '18 at 21:30

answered May 08 '18 at 21:15

wally

10,717
5
39
72

Silly me I think i get now @wally – Charles May 08 '18 at 21:21
So it performing a boolean logic with OR 100V10-->110 cause this makes alot of sense – Charles May 08 '18 at 21:27

score 0 · Answer 3 · answered May 08 '18 at 21:21

It is simple. '|' is called bitwise operator. It will return 1 if either of bits are 1. If both bits are 0, this operator will return 0.

x = 2 which is 0000 0010 (in bits representation) y = 4 which is 0000 0100

now if you apply '|', the result will become 0000 0110 which is 6.

How does "|" operator evaluate two integers?

3 Answers3