Swapping variables without dummy

This seems to be Old Programming School Practise. Came to know from Ariya.

a ^=b;
b ^=a;
a ^=b;

In C Programming, ^ stands for Exclusive OR.

Lets expand this expression and denote an and bn for new values of a and b then,

bn = b xor ( a xor b) = b xor a xor b = a
an = a xor ( b xor a) = a xor b xor a = b