Swap the Values of Two Variables Without Using a Third Variable

I have to say that I'm upvoting this - it's wonderful.

The real value in this question is to ask a candidate what's wrong with this article. There are just so many things wrong with it that it's a great starting place for any number of technical conversations.

This is particularly good:

  a = a*b
  b = a/b
  a = a/b

What if b==0? How accurate is it if a and b are floats? So many technical launching points.