[Resolved] Very Basic Comparison Problem

[cbj4074]

I'm ashamed I even have to post this question at this point in my career. Here's some code:

<?php
$string = 'hello';
//if the string 'hello' is not equal to 'goodbye' or 'aurevoir' or 'adios'...
if ($string != 'goodbye' || $string != 'aurevoir' || $string != 'adios') {
	echo "The string '$string' didnt match any of the acceptable strings!<br />";
}

$action = 'add';
//if the action 'add' is not equal to 'add' or 'modify' or 'drop'...
if ($action != 'add' || $action != 'modify' || $action != 'drop') {
	echo "The action '$action' is not an acceptable action!";
}
?>

These two scenarios, so far as I can tell, are identical. The only difference is that in the second scenario, the variable IS one of the three I'm checking for, yet the echo statement is still being run. Can anyone explain this to me???

Many thanks,

Ben

[nemonoman]

'add' is !='modify'

so the second comparison is true.

You want ANDs, not ORs, if you don't want the second statement to run:
if ($action != 'add'&&$action != 'modify' &&$action != 'drop') {

[drew010]

you are gonna want AND logic.

if the string is not goodbye, AND its not aurevoir, AND its not adios, then it is none of them.

shorten the logic and you'll see it makes sense as and.

$string = 'goodbye';
if ($string != 'aurevoir' && $string != 'goodbye') {

that will evaluate as 
if (0 && 1)
which evals to
if ( 0 )
which doesnt execute the brackets.

here is it with or.

$string = 'goodbye';
if ($string != 'aurevoir' || $string != 'goodbye') {
if (0 || 1)
evals to
if (1)
so the brackets are executed.

an or only needs one condition to match, while an and needs all conditions to match.

[cbj4074]

Makes perfect sense, thank you very much good sirs 😃