Invent something small and evil which to be almost invisible and to cause lot of troubles to catch like:
#define struct union
#define double float
#define floor ceil
#define true (__LINE__&42) !=42
#define private public
You can code the solution in any programming language during the weekend and have to submit it to email@example.com latest on Sunday September 8st.
On Monday we will upload the solutions on GitHub https://github.com/OLIMEX/WPC
You can play with your real name or with nick if you want to be anonymous, we will not disclosure your personal info if you do not want to.