of course this should be clear, but i think it has to be mentioned espacially:

AND is not the same like &&

for example:

<?php $a && $b || $c; ?>
is not the same like
<?php $a AND $b || $c; ?>

the first thing is
(a and b) or c

the second
a and (b or c)

'cause || has got a higher priority than and, but less than &&

of course, using always [ && and || ] or [ AND and OR ] would be okay, but than you should at least respect the following:

<?php $a = $b && $c; ?>
<?php $a = $b AND $c; ?>

the first code will set $a to the result of the comparison $b with $c, both have to be true, while the second code line will set $a like $b and THAN - after that - compare the success of this with the value of $c

maybe usefull for some tricky coding and helpfull to prevent bugs :D

greetz, Warhog

Operator are used to perform operation.

Operator are mainly divided by three groups.
1.Uniary Operators that takes one values
2.Binary Operators that takes two values
3.ternary operators that takes three values

Operator are mainly divided by three groups that are totally seventeen types.
1.Arithmetic Operator
+ = Addition
- = Subtraction
* = Multiplication
/ = Division
% = Modulo
** = Exponentiation

2.Assignment Operator
     = "equal to

3.Array Operator
    + = Union
    == = Equality
    === = Identity
    != = Inequality
    <> = Inequality
    !== =    Non-identity

4.Bitwise Operator
& = and 
^ = xor
| = not
<< = shift left
>> = shift right

5.Comparison Operator
==  = equal
=== = identical
!=  = not equal
!== = not identical
<>  = not equal
< = less than
<= less than or equal
> = greater than
>= = greater than or equal
<=> = spaceship operator

6.Execution Operator
 `` = backticks  

7.Error Control Operator
    @ = at sign

8.Incrementing/Decrementing Operator
    ++$a = PreIncrement
    $a++ = PostIncrement
    --$a = PreDecrement
    $a-- = Postdecrement

9.Logical Operator
    && = And
    || = Or
    ! = Not
    and = And
    xor = Xor
    or = Or

10.string Operator
    . =  concatenation operator
    .= concatenating assignment operator

11.Type Operator
    instanceof = instanceof

12.Ternary or Conditional operator
   ?: = Ternary operator

13.Null Coalescing Operator
    ??" = null coalescing 

14.Clone new Operator
    clone new = clone new

15.yield from Operator

    yield from = yield from

16.yield Operator
    yield = yield

17.print Operator
    print = print

Other Language books' operator precedence section usually include "(" and ")" - with exception of a Perl book that I have. (In PHP "{" and "}" should also be considered also). However, PHP Manual is not listed "(" and ")" in precedence list. It looks like "(" and ")" has higher precedence as it should be.

Note: If you write following code, you would need "()" to get expected value.

<?php
$bar = true;
$str = "TEST". ($bar ? 'true' : 'false') ."TEST";
?>

Without "(" and ")" you will get only "true" in $str. 
(PHP4.0.4pl1/Apache DSO/Linux, PHP4.0.5RC1/Apache DSO/W2K Server)
It's due to precedence, probably.

The variable symbol '$' should be considered as the highest-precedence operator, so that the variable variables such as $$a[0] won't confuse the parser.  [http://www.php.net/manual/en/language.variables.variable.php]