View controllers become more interesting when the user has a way to switch between them. Throughout the book, you will learn a number of ways to present view controllers. In this chapter, you will create a UITabBarController that will allow the user to swap between the ConversionViewController and the UIViewController displaying the map.
UITabBarController keeps an array of view controllers. It also maintains a tab bar at the bottom of the screen with a tab for each view controller in its array. Tapping on a tab results in the presentation of the view of the view controller associated with that tab.
Open Main.storyboard and select the View Controller. From the Editor menu, choose Embed In → Tab Bar Controller ...