Learn C
You compile, you print, and you read what the compiler tells you.
The edit, compile, read the verdict loop.
Reading a compiler diagnostic and fixing the line it points at.
Integer types, implicit conversions, promotions and overflow.
Branching and the three loop forms, chosen on purpose.
Reading argc and argv, and reporting a bad invocation.
Unlocks at 280 Chapter XP or when every required exercise is passed.