Game Show Program

Before you are three boxes.  One has a prize, two do not.  The game show host asks you to chose one box.  Then, he surprises you by telling you which one of the two remaining boxes does NOT contain the prize.  He then asks if you would like to switch your pick with the last remaining box.  What should you do?  This program proves if you choose to swap your pick for the last remaining box, your odds of winning double.