Nice game
I enjoyed this game with the spare time I had.
This however isn't exactly the best teaching material as some people may believe it to be. For one thing, it's good practice not to execute "extra" commands and stuff if you really have to. This game may or may not encourage that, but it's just a personalized high score. And another thing, as a good programmer, you should know very well what to expect of the program if you've done it correctly (and if you didn't, well, you learn). Make incentives to try to get the puzzle done in the first go. I know the last few statements may be a bit contradicting when it comes to testing code bit by bit, but this is a puzzle with simple elements really.
One last thing: I cried when I realized I couldn't do crazier things like recursions or loops because there's no such thing as escape conditions =(