A general verdict upon a plea of not guilty, is either “guilty,” or “not guilty,” which imports a conviction or acquittal of the offense charged. Upon a plea of a former conviction or acquittal of the same offense, it is either “for the state,” or “for the defendant.” When the defendant is acquitted on the ground that he was insane at the time of the commission of the act charged, the verdict must be “not guilty by reason of insanity.” When the defendant is acquitted on the ground of variance between the charge and the proof, the verdict must be “not guilty by reason of variance between charge and proof.”