For some reason xCode is not finding the SDL_BlitSurface(). I get a build error and the build fails. There must be some reason, I can't figure out what it is though.
SDL_BlitSurface draws one SDL_Surface onto another SDL_Surface. The third argument has to be a SDL_Surface. In your program the third argument is a SDL_Window.
I don't know for sure because I haven't used SDL2 much yet but maybe you find SDL_GetWindowSurface useful.
I used SDL_GetWindowSurface on line 39. Thank you for going through and figuring out I used the wrong arguments! That was the problem, the build succeeds now.