struct Car {
    let model: String
    let numberOfSeats: Int
    private(set) var currentGear = 0
    private static let upshiftRange = 0..<10
    private static let downshiftRange = 1...10

    init(model: String, numberOfSeats: Int) {
        self.model = model
        self.numberOfSeats = numberOfSeats
    }

    mutating func upShift() {
        if Car.upshiftRange.contains(currentGear) {
            currentGear += 1
            print(currentGear)
    }

    mutating func downShift() {
        if Car.downshiftRange.contains(currentGear){
            currentGear -= 1
            print(currentGear)
        }
    }

}