Why use bitwise OR / AND

It can seem this way if your looking at the values as decimal or hex

These operations are a binary operation so it works on ones and zeroes

For example the decimal number 15 is 0F in hex or 00001111 in binary

If I and 16 with 4 I will get 4, why well consider the binary value

0000 1111 <-- 16

0000 0100 <-- 4

Only where the ones align will you have a 1 left in the answer, therefor you get 00000100 or 4

It can appear random if your looking at the number in decimal

Now the opersit is more confusing

Given

01010011 <-- 83 anded  with

10010101 <-- 149 results in

00010001 <-- 17

Looking at this in decimal would be really confusing but looking at it in binary it makes perfect sense. So again only where the ones match are you left with a one. With the OR operator it wirks that you get a one where ever there is a one on either or both sides (But no carry)

So

10101010 OR

01010101 =

11111111

Then again

11110000 OR

00000000 =

11110000

Hope that clarifies the issue

Also the binary notation has values like this

128, 64, 32, 16, 8, 4, 2, 1 and to get to the decimal just add up where each bit has a one aligned with it

In low-level programming, you often use an integer to represent a collection of single bit fields, or fields that are only a few bits wide.  The bit-wise operators are useful for checking the values of those fields or changing individual bits.  A good example in GNU/Linux is the "file mode" field that represents permissions as a bit vector, often shown in octal.  For example, "0664" = 110.110.100 means that the file is readable and writable by its owner and its group, but to the world it's read-only.

Data communications protocols often use individual bits and short fields in headers for various control purposes.

Bit-wise AND and OR are often used for device registers, where individual bits may represent the values of GPIO inputs or outputs.

Bit-wise XOR is often used for making linear-feedback shift registers, which may be used as pseudo-random number generators.

Thanks guys. You have been very helpful.

Sometimes one operand word is data and the other is a mask.  Let's say that three separate binary events in I/O land are required to draw a conclusion.  By using the mask we can check the conditions in parallel, rather than sequentially.  Saves time.

Easier to modify.

Sometimes, when working with this, it is better to have your numbers represented as hexadecimal.  Then your numerals correspond to four-bit groups.  Makes it easier to reckon in.