Swapping Two Numeric Variables In Only Three Instructions

Having done this in the past, needing it again and finding this page:

• http://wiki.answers.com/Q/How_do_you_write_a_program_in_C_to_swap_two_variables_without_using_the_third_one

I've found that two numerics can be swapped quite easily without the use of a third variable:

a = a + b
b = a - b
a = a - b

Neat.