Given two variables, A and B say, exchange their values so that A has the previous value of B and B has the previous value of A.
The simple solution is to use a third variable:
<? // set values for the variables $a = 3; $b = 7; // save a to a new variable called c $c = $a; // a is now stored somewhere else, so override it with b $a = $b; // b is now stored in a, so update that to c $b = $c; // output the variables echo 'A = ' . $a . ', B = ' . $b; ?>Which produces:
A = 7, B = 3