if let someting = possiblyNil {
        print("not a nil")
    }
    else{
        print("nil")
    }

    struct Toddler {
        var name: String
        var monthsOld: Int
    
        init?(name: String, monthsOld: Int){
            if monthsOld < 12 || monthsOld > 36 {
                return nil
            } else {
                self.name = name
                self.monthsOld = monthsOld
            }
        }
    }

    if let theResidence = person.residence {
        if let theAddress = theResidence.address {
            if let theApartmentNumber = theAddress.apartmentNumber{
                    print(theApartmentNumber)
            }
        }
    }

    if let theApartmentNumber = person.residence?.address?.apartmentNumber {
        print(theApartmentNumber)
    }

    let pets = allClientAnimals()
    
    for pet in pets {
        if let dog = pet as? Dog {
            walk(dog: dog)
        } else if let cat = pet as? Cat{
            cleanLitterBox(cat: cat)
        } else if let bird = pet as? Bird{
            cleanCage(bird: bird)
        }
    }

    class SecondViewController : UIViewController{
        var name: [String]?
    }
    
    func prepare(for segue: UIStoryboardSegue, sender: Any?){
        let secondVC = segue.destination as! SecondViewController
        secondVC.names = ["Peter", "Jamie", "Tricia"]
    }

    var items: [Any] = [5, "bill", 6.7, true]
    if let firstItem = items[0] as? Int{
        print(firstItem + 4)
    }

    func singHappyBirthday(){
        if birthdayIsToday{
            if !invitedGuests.isEmpty{
                if cakeCandleLit{
                    print("Happy Birthday to you!")
                } else{
                    print("The cake's candles haven't been lit.")
                }
            } else {
                print("It's just a family party.")
            }
        } else {
            print("No one has a birthday today.")
        }
    }

    func singHappyBirthday(){
        guard birthdayIsToday else{
            print("No one has a birthday today.")
            return
        }
        
        guard !invitedGuests.isEmpty else{
            print("It's just a family party.")
            return
        }
    
        guard cakeCandleList else{
            print("The cake's candles haven';t been lit.")
            return
        }
    
        print("Happy Birthday to you!")
    }

    if let eggs = goose.eggs {
        print("the goose laid \(eggs.count) eggs.")
    }

    guard let eggs = goose eggse else {return}
    print("the goose laid \(eggs.count) eggs.")

    calculateResult(a: 4, b: 8, c: nil)
    
    func calculateResult(a: Int?, b: Int?, c: Int?) -> Int{
        guard let aValue = a else {return 0}
        guard let bValue = b else {result aValue}
        guard let cValue = c else {result bValue}
        return aValue + bValue + cValue
    }