how to compare a variable with multiple values-CodePudding

Hello everyone I would like to be able to compare the country variable with country values and if the country variable is not in my list display an error I have a code but it does not work

else if($country  <> "Belgique")or ($country   <> "Luxembourg") or ($country   <> "France")or($country   <> "Pays-bas")
 {echo "The country variable is not in the list "; }

CodePudding user response：

You can use in_array function instead of many if else.

$country_list = array("Belgique", "Luxembourg", "France", "Pays-bas");
if(!in_array($country, $country_list)) {
   echo "The country variable is not in the list";
}

CodePudding user response：

Firstly, you have a fairly straight-forward syntax error: the syntax of an if statement is if ( condition ) Note those parentheses - they're part of the if statement itself, not the condition. When you write this:

if ( $country <> "Belgique" )

The condition is this:

$country <> "Belgique"

So if you want the condition to be this:

($country <> "Belgique") or ($country <> "Luxembourg") or ($country <> "France") or ($country <> "Pays-bas")

Then you have to put the whole thing inside the parentheses of the if statement:

if ( ($country <> "Belgique") or ($country <> "Luxembourg") or ($country <> "France") or ($country <> "Pays-bas") )

Secondly, you have made a common mistake in translating English (or whatever your first language is) into formal logic: it's tempting to assume that ($country <> "Belgique") or ($country <> "Luxembourg") means "$country is neither Belgique nor Luxembourg", but it actually means "if $country is not Belgique then evaluate to true; also, if $country is not Luxembourg then evaluate to true".

If you provide "Luxembourg", the first part is true; if you provide "Belgique", the second part is true; in fact, since no value of $country is both Belgique and Luxembourg at once, the result is always true!

What you actually wanted to say was "if $country is not Belgique and also $country is not Luxembourg, then evaluate to true": ($country <> "Belgique") and ($country <> "Luxembourg")

So:

if ( ($country <> "Belgique") and ($country <> "Luxembourg") and ($country <> "France") and ($country <> "Pays-bas") )

(This fact that not ( A or B ) is equivalent to ( not A ) and ( not B ) is known as De Morgan's Law.)

As a side note, in PHP, and and or are not quite the same as && and ||. See stackoverflow.com/questions/4502092/php-and-or-keywords

Although it doesn't make any difference in this case, because you've grouped things neatly with parentheses, && and || are more often the operators you want, giving:

if ( ($country <> "Belgique") && ($country <> "Luxembourg") && ($country <> "France") && ($country <> "Pays-bas") )

<> is identical in meaning to !=, but there is also the stricter !==, see How do the PHP equality (== double equals) and identity (=== triple equals) comparison operators differ? and Is there a difference between !== and != in PHP?

So you might actually want this:

if ( ($country !== "Belgique") && ($country !== "Luxembourg") && ($country !== "France") && ($country !== "Pays-bas") )