Bad Programming Practices

Each post must contain one bad programming practice to add to the list. I'll start:

In C++, overload library functions by using #define. That way it looks like you are using a familiar library function where in actuality you are using something totally different.

>>16
Please learn about monoids, thank you.
(+) is a natural candidate for the monoidal operation because it is always associative _{and usually commutative}.