I'm going to attempt to explain this minor dilemma as best as I can, so bear with me as these are rookie note reading questions.

First rookie note reader question: In the very next following measure, if there is no indication of the A's or D's being sharp or natural, then they are again played natural. Right? Or are they sharp in all following measures until indicated somewhere as again to be played as a natural? My understanding has always been (and I could be wrong here) if a D as an example is marked sharp within a given measure and in the following measure the D's are not indicated as being sharp or natural (i.e., no marking either way), then the D's are played natural.
Second rookie note reader question: If the right hand (top line / top stave in a 3 stave arrangement) D in a given measure is marked as a sharp, are all D's in the below corresponding measures also sharp even if not indicated as sharp, or would they / should they also be marked as sharp?
Any help or something I could read or see as a visual here would greatly help.
Thanks,
Marc