Logical Interview Question

 1. How to Swap two variables, With or without the third variable & inbuild function.

This method will work for any variable type:

$a = 5;
$b = 6;
list($a, $b) = array($b, $a);
print $a . ',' . $b; // 6,5

Another simple way (which only works for numbers, not strings/arrays/etc) is
$a =  $a + $b;  // 5 + 6 = 11
$b = $a - $b;   // 11 - 6 = 5
$a = $a - $b;  // 11 - 5 = 6
print $a . ',' . $b; // 6,5