• Variable is set if it has been assigned a value other than NULL.
• Even if a variable is assigned an empty string (""), it is set.
• Variable is empty if it is an empty string (""), 0, "0", false, NULL, array(), and a variable declared but not given a value are all empty.

empty() function: returns true for the following values:
empty string (""), 0, "0", NULL, or FALSE

isset() function: returns false when the variable is NULL, that is, not initialized or given a value.

//both return false using isset() function
//$myvar;
//$myvar = NULL;

// Example1:
//returns true using empty() function
$myvar=0;

// Evaluates to true because $myvar contains 0
if (empty($myvar)) 
{
  echo '$myvar is either empty string, 0, "0", empty, NULL, or FALSE';
}

else
{
  echo '$myvar contains a value';
}

// Example2:
//returns false using empty() function
$myvar=5;

// Evaluates to false because $myvar contains 5
if (empty($myvar)) 
{
  echo '$myvar is either 0, "0", empty, NULL, or FALSE';
}

else
{
  echo '$myvar contains a value';
}

// Example3:
// Evaluates as true because $myvar is initialized
if (isset($myvar)) 
{
  echo '$myvar is initialized';
}

else
{
  echo '$myvar does not contain a value';
}

// Example4:
//unset() destroys specified variables
unset($myvar);

// var_dump() returns NULL
var_dump($myvar);

// Example5:
// Evaluates as false because $myvar is destroyed
if (isset($myvar)) 
{
  echo '$myvar is initialized';
}

else
{
  echo '$myvar does not contain a value';
}

Example1:
$myvar is either 0, "0", empty, NULL, or FALSE

Example2:
$myvar contains a value

Example3:
$myvar is initialized

Example4:

Warning: Undefined variable $myvar in D:\InetPub\vhosts\mjowett-1638.package\qcitr.com\wwwroot\demos\isset_vs_empty.php on line 152
NULL

Example5:
$myvar does not contain a value