func commandLine() {
    var doubleArray = [Double]()

    while doubleArray.count < 3 {
        print("Please enter a double number")
        if let numberString = readLine() {
            if let numb = Double(numberString) {
                doubleArray.append(numb)
            } else {
                print("Please enter a valid number!")
            }
        }
    }
}