[0xmohit]

  One day I'll have to work with people who learned from
  this (and others like it), and it will be a long painful road
  to help them unlearn.

Quoting from the link you've mentioned:

  #define add(a, b) a + b

I couldn't agree with you more.

--

To elaborate:

  add(1, 8) * add(5, 1)

wouldn't yield 9 * 6 = 54, but

  1 + 8 * 5 + 1

which is 42. One might say that it's correct, since it's the Answer to the Ultimate Question of Life, the Universe and Everything.

[greenyoda]

Which is why anyone who has experience programming in C would instead write:

  #define add(a, b) ((a) + (b))

[0xmohit]

One may also do:

  add(x, foo(x))

Which is why anyone who has experience programming in C would use (an inline) function instead.