PHP isset() with multiple parameters

The isset() function in PHP can take multiple parameters, and it will return TRUE if all of the variables passed to it have been set, and FALSE if any of them have not. For example:

<?php

$a = "Hello";
$b = "World";

if (isset($a, $b)) {
    echo "Both variables are set.";
} else {
    echo "One or both variables are not set.";
}

Watch a video course Learn object oriented PHP

This will output "Both variables are set." because both $a and $b have been assigned values.

<?php

$a = "Hello";
$b;

if (isset($a, $b)) {
    echo "Both variables are set.";
} else {
    echo "One or both variables are not set.";
}

This will output "One or both variables are not set." because $b is not assigned any values.