Swift - Calc

import Glibc

var index: String?;
while index != "4" {
  system("clear")
  print("--- KALKULATOR SWIFT ---")
  print("Wybiarz pole oraz obwod ktorej figury chcesz liczyc:")
  print("1. Kwadrat")
  print("2. Trojkat")
  print("3. Prostokat")
  print("4. Koniec")
  index = readLine()
  system("clear")

  switch index {
    case "1" :
      print("--- KWADRAT ---")
      print("Podaj a:")
      var a = readLine()
      let numA = Double(a!)
      print("Pole: \(Double(numA!) * Double(numA!))")
      print("Obwod: \(4 * Double(numA!))")
      a = readLine();
      break
    case "2" :
      print("--- TROJKAT ---")
      print("Podaj a:")
      var a = readLine()
      let numA = Double(a!)
      print("Podaj b:")
      let b = readLine()
      let numB = Double(b!)
      print("Podaj c:")
      let c = readLine()
      let numC = Double(c!)
      print("Pole: \(Double(numA!) * Double(numB!)/2)")
      print("Obwod: \(Double(numA!) + Double(numB!) + Double(numC!))")
      a = readLine();
      break
    case "3" :
      print("--- PROSTOKAT ---")
      print("Podaj a:")
      var a = readLine()
      let numA = Double(a!)
      print("Podaj b:")
      let b = readLine()
      let numB = Double(b!)
      print("Pole: \(Double(numA!) * Double(numB!))")
      print("Obwod: \(2 * Double(numA!) + 2 * Double(numB!))")
      a = readLine();
      break
    default:
      break
  }
}