<?php

$a=10;
$b=20;

echo "Value of a: $a</br>";
echo "Value of b: $b</br>";

$a=$a+$b;
$b=$a-$b;
$a=$a-$b;

echo "Value of a: $a</br>";
echo "Value of b: $b</br>";

?>
/*

Output
	
Value of a: 10
Value of b: 20
Value of a: 20
Value of b: 10