If a string is not matching one of 3 option in PHP

Question

This is the code I used to have to check if $A doesn't match $B

if($A!=$B) {
    $set = array();
    echo $val= str_replace('\\/', '/', json_encode($set));
    //echo print_r($_SERVER);
    exit;
}

Now I need the opposite of this condition: ($A need to match one of these $B,$C or $D)

Answer 1

A simple shortcut to seeing if a value matches one of multiple values you can put the values to be compared against ($B, $C, and $D) into an array and then use in_array() to see if the original value ($A) matches any of them.

if (in_array($A, [$B, $C, $D])) {
   // ...
}

If you don't want it to match any of $B, $C, or $D just use !:

if (!in_array($A, [$B, $C, $D])) {
   // ...
}