(a) No person holding office under the United States shall be eligible to the office of county controller during continuance in such office, nor until one year thereafter.

(b) The county commissioners, county treasurer, prothonotary, register of wills, clerk of the courts, recorder of deeds, sheriff and district attorney, and their chief clerks or deputies, shall be ineligible, during their continuance in such office and for two years thereafter, to the office of county controller.

(c) The controller shall always be eligible to reelection or appointment.