Isset Command in PHP

Let us have the following variable:

<?php
	$test = null;
?>

Let's write a condition that checks that the variable is not equal to null:

<?php
	$test = null;
	
	if ($test !== null) {
		echo '+++';
	} else {
		echo '---';
	}
?>

Such a check can be performed more conveniently using a special command isset:

<?php
	$test = null;
	
	if (isset($test)) {
		echo '+++';
	} else {
		echo '---';
	}
?>

You can perform the reverse check, that the variable is not defined. To do this, we will perform inversion of isset using the logical NOT:

<?php
	$test = null;
	
	if (!isset($test)) {
		echo '+++';
	} else {
		echo '---';
	}
?>

Modify the following code according to the studied theory:

<?php
	$test = null;
		
	if ($test == null) {
		echo '+++';
	} else {
		echo '---';
	}
?>

Modify the following code according to the studied theory:

<?php
	$test = null;
		
	if ($test != null) {
		echo '+++';
	} else {
		echo '---';
	}
?>