It was an interesting way to swapping the values of two variable.There are several ways to do that.I just tried two of the techniques using php5 that was like as belows:

Created a file called class.Swap.php .

It contained the following codes:

<?php
class Swap{
    private $a = 2;
    private $b = 5;
    private $x = 13;
    private $y = 3;
    public function before_swap(){
        echo '<h2>The values Before Swap</h2>';
        echo '<br>';
        echo " Value of A = ".$this->a;
        echo '<br>';
        echo " Value of B = ".$this->b;
        echo '<br>';
        echo " Value of X = ".$this->x;
        echo '<br>';
        echo " Value of Y = ".$this->y;
        echo '<br>';
    }
    public function swap1(){
        echo '<h3>The values After Swap Technique 1</h3>';

        $this->a = $this->a+$this->b;
        echo '<br>';
        $this->b = $this->a-$this->b;
        $this->a = $this->a-$this->b;
        echo "value of A= " ."$this->a"."<br>"."value of B= " ." "."$this->b";
    }
    public function swap2(){
    echo '<h3>The values After Swap Technique 2</h3>';
        $this->x = $this->x * $this->y;//$x = 13,$y = 3 now $x =39
        $this->y = $this->x / $this->y;
        $this->x = $this->x / $this->y;
    echo "value of X= " ."$this->x"."<br>"."value of Y= " ." "."$this->y";
    }
}
?>

<?php
include 'swap_oop.php';
$objSwap = new Swap();
$objSwap->before_swap();
$objSwap->swap1();
$objSwap->swap2();
?>