interactive BASIC interpreter
That's the sort of thing you get with the DuinoMite-style boards and I think that would be easier than the way we used to learn C, ie with no forums, a cross-compiler, and a screen with
written on it. Hmmm now what?
But yes these days with the Arduino you don't have that problem as there are many examples that work out of the box so it's easy to start with say the blink example and play with it to get an idea of how C works. Then work your way up asking questions along the way.
Bottom line then, learn C.
PS: has the original post changed, it no longer mentions BASIC.