generate random image over a button

I'm working on a project to generate random images from an array. I'm running into an issue. I will have one button on the screen name "generage shapes". Once the user clicks on this button the "generate shapes" button becomes hidden and 4 buttons display 4 different shapes. I'm having an issue making these 4 buttons display with the image from my array. I tried a switch statement but it doesn't go through. I'm providing my code below. Please let me know if you can help.

Thank you

import UIKit

class ShapesDetailViewController: UIViewController {

var random = arc4random_uniform(4)

@IBOutlet weak var titleBar: UINavigationItem!

@IBOutlet weak var displayMessageLabel: UILabel!

var myImages = [ "diamond.png", "decagon.png", "dodecagon.png", "hectagon.png", "heptagon.png", "octagon.png", "parallelogram.png", "pentagon.png", "rectangle.png", "rightTriangle.png", "square.png", "trapezoid.png", "triangle.png"]







//my image labels


@IBOutlet weak var buttonOne: UIButton!
@IBOutlet weak var buttonTwo: UIButton!
@IBOutlet weak var buttonThree: UIButton!
@IBOutlet weak var buttonFour: UIButton!

@IBOutlet weak var generateImage: UIButton!

override func viewDidLoad() {

    self.buttonFour.hidden = true
    self.buttonOne.hidden = true
    self.buttonThree.hidden = true
    self.buttonTwo.hidden = true
    displayMessageLabel.hidden = true



}

@IBAction func generateRandomImages(sender: AnyObject) {


    displayMessageLabel.hidden = false


    buttonOne.hidden = false


    switch(random){

    case 0: buttonOne.imageView?.image = UIImage(named: "circle.png")
        break

    case 1: buttonOne.imageView?.image = UIImage(named: "decagon.png")
        break

    case 2: buttonOne.imageView!.image = UIImage(named: "diamond.png")
        break

    case 3: buttonOne.imageView!.image = UIImage(named: "hectagon.png")
        break
    default:
        break;

    }



    generateImage.hidden = true

}


}