PHP Program to Swap two values without third variable

Php Program to Swap two values without third variable of a number

<?php
if(isset($_POST['submit']))
{
$value1=$_POST['num1'];
$value2=$_POST['num2'];
$value1=$value1+$value2;
$value2=$value1-$value2;
$value1=$value1-$value2;
        echo "Value of first variable after swapping" .$value1."<br />";
        echo "Value of second variable after swapping"  .$value2;
}



?>
<!DOCTYPE html>
 <html>
 <head>
 <title>Swap two values without third Variable</title>
 </head>
 <body>
 <form name="factorial" action="" method="post">
 Number 1 :<input type="text" name="num1" value="" required=""><br /><br />
 Number 2 :<input type="text" name="num2" value="" required=""><br />
 <input type="submit" value="Submit" name="submit">
 </form>
 </body>
 </html>