All elective state, district, and county officers, and the United States senators, and the members of the United States house of representatives, must be elected at the general election next preceding the expiration of the term of each such officer. In a year when a president and vice president of the United States are to be chosen, a number of presidential electors equal to the number of senators and representatives to which this state is entitled in the Congress of the United States must be elected at such general election.