In this challenge, we want to practice using Structs, for loops, and properties.
Add a Label, a ToolBar, UIImageView as the background, and a barButtonItem entitled next on the toolbar. Start by creating a struct to model a Balloon. The Balloon should know it's number and what image it has. Next, create a function that creates 99 balloons and randomly assigns one of the 4 images to the created Balloon instance. Use a switch statement to assign each of the four Balloon images. Add these all to an array property in the ViewController.
When pressing the button a few things should occur.
Update the balloonsLabel with the number of the Balloon. Update the imageView with the Balloon instances image.