[RESOLVED] Text string comparison using 'not' logic

sherry

Hello.

What causes a string comparison to work using '==' but when using the '!=' or '!==', it doesn't work properly?

For example, I have in an variable versions of a word like 'allocate' in an array which is placed into a variable, '$status' in a 'foreach' loop. In an 'if' statement, I have the following:

DOESN'T WORK PROPERLY:

$status = $status_array[$i];

if (($status != "allocate1") || ($status != "allocate2") || ($status != "allocate3")) {
  // do something
}

WORKS PROPERLY:

$status = $status_array[$i];

if (($status == "allocate1") || ($status == "allocate2") || ($status == "allocate3")) {
  // do something
}
else { 
// do something
}

Why would one method work and not the other? I'd rather use the 'short' version (without the 'else').

Thanks in advance.

EDIT: meant to add the '||' statements

bradgrafelman

That's because || isn't the correct operator to use here:

if (($status != "allocate1") || ($status != "allocate2") || ($status != "allocate3")) {

Examine your logic here: you're saying, in plain English: "If $status isn't allocate1, OR $status isnt allocate2, OR $status isn't allocate3."

Obviously, this logic will match any string. Instead, you should be using &&.

sherry

Wow, ... and I know that. I guess I need to take a smoke break (and I don't even smoke) 🙂

Thanks bradgrafelman!

Have a good one!

Weedpacket

To expand a little further:

if(($status == "allocate1") || ($status == "allocate2") || ($status == "allocate3"))

This test passes if and only if $status is equal to "allocate1" or "allocate2" or "allocate3". If you want it to fail instead, you have to negate the entire test:

if(!(($status == "allocate1") || ($status == "allocate2") || ($status == "allocate3")))

But since that is starting to get messy, it pays to recall a small fact of elementary logic which is that "not(A or 😎" is equivalent to "(not A) and (not 😎". Applying that fact to the above line leads to bradgrafelman's answer.

sherry

Well weedpacket...

Regarding the 'fail' test, I learned something new. Thanks! I'm sure I'll use it sometime in the future.

Take care.