The rule of accidentals is an accidental (sharp or flat) carries over an entire measure unless one or more notes has a natural symbol before it. The key signature also puts the rule of accidentals into action. If it is in the G major key signature, every "F" will become "F sharp", unless one "F" has a natural or a flat on it. If it does not, the key signature overides it. If there is a sharp or flat in the previous measure, there will not be a sharp or flat in the next measure unless: the key signature claims something different or there is a sharp or flat in the measure the note is in.
The rule of accidentals is an accidental (sharp or flat) carries over an entire measure unless one or more notes has a natural symbol before it. The key signature also puts the rule of accidentals into action. If it is in the G major key signature, every "F" will become "F sharp", unless one "F" has a natural or a flat on it. If it does not, the key signature overides it. If there is a sharp or flat in the previous measure, there will not be a sharp or flat in the next measure unless: the key signature claims something different or there is a sharp or flat in the measure the note is in.