If you get discouraged after spending 15 minutes fooling around with wondering why you can't stick a string into an int, then I'd suggest just giving up now.
If you really are serious, then you need to find a good C++ book or take a class. I've seen this book recommended by a C++ expert before, and it looks decent enough:
amazon link
The DS is NOT the place to begin learning programming, you will get stuck on a lot of little things to do with the hardware, and not being polished, etc. First get some practice writing & debugging on a more mature platform which has better debugging tools available (ie, your PC).
And finally: Something like a port of zelda, or starcraft, is waaay too big for a first project. Usually, the life of a homebrewer goes something like this: Pong -> Tetris -> Big project which 90% of the time gets abandoned. Don't skip straight to the 3rd step, at least get the first two under your belt