My first app.. Help please!

//: Playground - noun: a place where people can play

import UIKit
import XCPlayground
import GameKit

// Create fake labels
let headsCountLabel = UILabel()
let tailsCountLabel = UILabel()
let currentSideLabel = UILabel()

// MARK: - Sides enum

// Lets start with an enum call Sides
// For now, let's assume objects only have two sides:
// Top and Bottom.
enum Side {
    case Top
    case Bottom
}

// MARK: Flippable protocol

// Let's describe objects that can be flipped to either
// of the Side enum sides via the Flippable protocol
protocol Flippable {

    // Flippable objects always have a upper side
    var upperSide: Side { get set}

    // We also want to be able to get the name of the
    // upper side of a Flippable
    var upperSideName: String { get }
}

// Moreover, let's extend the flippable protocol
// with a standard behaviour when the object is flipped:
// it assigns uppersSide a random side
extension Flippable {

    // Flip the coin, that is assign a random side
    // to upperSide
    mutating func flip(){
        let randomNumber = GKRandomSource.sharedRandom().nextIntWithUpperBound(2)
        switch randomNumber {
        case 0: upperSide = .Top
        case 1: upperSide = .Bottom
        default: upperSide = .Top
        }
    }
}

// MARK: - The Coin

// Our Coin struct conforms to the Flippable protocol
// and as such can be flipped by calling flip()
// Moreover, it has to have a current upperSide
// and upperSideName value to conform to Flippable.
// Let's say the initial side is always Top
struct Coin: Flippable {

    var upperSide: Side = .Top

    var upperSideName: String {
        return upperSide == .Top ? "Heads" : "Tails"
    }
}

// MARK: - The Counters

struct Counters {

    var heads = 0
    var tails = 0

    // A convenience method to increment the counter
    // according to the result we pass in
    mutating func incremenet(forResult result: Side) {
        switch result {
        case .Top: heads += 1
        case .Bottom: tails += 1
        }
    }
}

// MARK: - Our app logic

// Create a counter
var counters = Counters()

// Create a coin...
var coin = Coin()

// ...and flip it 20 times
for _ in 1...20 {

    coin.flip()

    // Update the counter with the upper side
    counters.incremenet(forResult: coin.upperSide)

    // Update your views accordingly
    currentSideLabel.text = coin.upperSideName
    headsCountLabel.text = "\(counters.heads)"
    tailsCountLabel.text = "\(counters.tails)"

    // For the sake of this playground, let's also print to console
    // Note: never use ! in production
    print("Result: \(currentSideLabel.text!) - Heads: \(headsCountLabel.text!) - Tails: \(tailsCountLabel.text!)")
}