Operators

[thoand]

What is the difference between

if (!$a == $b) { ...

and

if ($a != $b) { ...

could read the manual but only found $a != $b

Thomas

[Kudose]

I do not know, I am only posting so I get an email telling me when a reply comes, becuase I am interested to know too.

🙂

[bubblenut]

!$a evaluates the oposite of the boolean value of $a, so if $a is true then !$a is false.
$a!=$b is saying the if $a is not equal to $b return true. !$a==$b is saying is the boolean inverse of $a equal to $b return true. So for the case you provided the result is the same. It's much like the difference between x/2=y and x=2y in algebra, they are essentially equivalent(sp? but I can't be bothered to check) but logically different.
The real conundrum arises when you provide a condition like
!$a < $b
if $a is 13 and $b is 12, $a is obviously greater than $b, but does that mean that the boolean inverse of $a is less than $b?
I think my example may be better described with a combination of negative and positive numbers but I'm a little drunk now and can't be bothered to think it through. If someone gets my drift please explain it better ... if, however, my drift is like that of an avalance, beutifull in it's grace of presence but ultimately thoroughly annoying in it's mindless destruction of order, please flame me away 😉 😃
Bubble

[drew010]

using the ! (not operand) will only work properly for a boolean expression, if you try it in another case like mentioned above: !$a < $b you wont get the expected results.

if you have this:
$a = 7;
echo !$a; //prints nothing but evals BOOL false

so to translate
$a = 7;
if (!$a < $b)
would be equal to saying
if (0 < $b)
!$a will always be 0 or false unless $a itself is 0 or false, in that case it will return 1 (true).

furthermore, you can study this:
$color = "blue";
$shape = "circle";
if( ($color == "blue") && ($shape == "square") )
the above if turns into:
if( (TRUE) && (FALSE) )
which evaluates in whole to false.
but if you had this:

if( ($color == "blue") && !($shape == "square") )
the above turns to:
if( (TRUE) && !(FALSE) )
which becomes:
if( (TRUE) && (TRUE) )
so the whole thing evaluates true.

so you can see ! negates the following boolean result.

for example you can have:
$color = "something";
if(!isset($color))
"if not isset(color)"
evals false, because isset color evals true and then it gets negated so it becomes false.

hope that helped also.

[Weedpacket]

And just to round this off, if($a!=$b) is equivalent to if(!($a==$b)); note the extra parentheses, which ensure that the equality is tested first, and then the result of that (true or false) is negated.