[nostrademons]

The #define else one is scarier to me. #define struct union will almost certainly crash immediately on runtime, as one member's a pointer and it gets overwritten by an int or a pointer to a different type. #define else just always runs all else clauses - the code is likely still valid, it just does something very different from what the author intended.

Both of them would be a real pain to debug.

[jongraehl]

Both would be easy to notice in a debugger. Finding the cause, as you imply, would be tricky unless you remember to check the preprocessed output.