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Posted by Kimmo Laine on 05/25/05 19:01
"Jam Pa" <anonanon@non-anon.org> kirjoitti
viestissδ:Xns9661B5FF25BABanonanonnonanonorgjp@213.243.153.2...
> Both '&' and '&&' are 'AND' right? Or what about 'ORs' '|' and '||'?
>
> Whats the difference? I not grok....
& and | are bitwise arithmetic operators while && and || are boolean
operators. What this maeans is that & and | handle single bits in and
integer, but && and || evaluate the entire integer as true or false.
For example we have and integer 4. when it is splitted in bits it looks like
0100
( = 0*(2^3) + 1*(2^2) + 0*(2^1) + 0*(2^0) )
And we have integer 8 that's 1000
( = 1*(2^3) + 0*(2^2) + 0*(2^1) + 0*(2^0) )
Now, comparing them (8 && 4) this returns TRUE, since both are none-zero
(there is at least one bit other than zero in both of them.
Bitwise operation on the other hand: 8 & 4 will return zero. This is because
it compares each single bit:
8 & 4 = 0
-----------
1 and 0 = 0
0 and 1 = 0
0 and 0 = 0
0 and 0 = 0
Now OR then. 4 || 8 returns TRUE, since within the two operators there is at
least one none-zero bit. Bitwise operation 8 | 4 returns 12. Let's see that
again in bitwise:
8 | 4 = 12
-----------
1 or 0 = 1
0 or 1 = 1
0 or 0 = 0
0 or 0 = 0
because 1100 is the binary representation of 12. It's not the same as 8 + 4,
that was just a coincidence. 8 | 8 returns 8. :)
8 | 8 = 8
-----------
1 or 1 = 1
0 or 0 = 0
0 or 0 = 0
0 or 0 = 0
See the difference? When using && and || we just look if the integer is zero
or non-zero, but using & and | (and xor ^) we perform bitwise arithmetic.
AND and OR are not the same as && and ||, but they are closer to them, than
to & and |. I never understood completely the difference, but there is a
section in the manual that trys to explain it, but I just can't find it now.
All I found was this: "The reason for the two different variations of "and"
and "or" operators is that they operate at different precedences. " (PHP
Manual). Operator precendence is all about in what order the expression is
evaluated.
--
"I am pro death penalty. That way people learn
their lesson for the next time." -- Britney Spears
eternal.erectionN0@5P4Mgmail.com
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