A
small additional note: In
music, an
accidental in "in effect" until the
end of the measure. Thus, if the first B in the
measure is an
accidental B-flat, then any other B's in the measure are also flat.
From a
compositional point of
view, the accidentals are there to allow you to use
notes that are not
properly "in" the
key you're writing in. So, while
all B's in the key of C are natural, you could slip in an
accidental if you really wanted a
B-flat, just this once. (Well, for the rest of the measure. Then again, if a
measure has
three B's, and the first is an
accidental flat, but the
second is an
accidental natural, then, well, the third is natural too.
Freaky, huh?)