The exchange operator changes the value of two variables. But not only that, the operator also allows a programmer to manipulate two values, before they are exchanged.
A simple example: We have two integers one called n0 and another one called n1. n0 has the value 10 and n1 the value 12. Then we exchange n0 and n1:
n0 <=> n1
Now n0 has the value 12 and n1 10. We exchange them again, but now we manipulate the values of the variables, before they are exchanged.
n0, n0 * 2 <=> n1, n1 + 3
Now n0 has the value 13 and n1 24.