public class Calculator
{

   private static int result; // Static variable where the result is stored

   public void add (int n)
   {
      result = result + n;
   }

   public void substract (int n)
   {
      result = result - 1; // Bug : should be result = result - n
   }

   public void multiply (int n)
   {} // Not implemented yet

   public void divide (int n)
   {
      result = result / n;
   }

   public void square (int n)
   {
      result = n * n;
   }

   public void squareRoot (int n)
   {
      for (; ;) ; // Bug : loops indefinitely
   }

   public void clear()
   {  // Cleans the result
      result = 0;
   }

   public void switchOn()
   {  // Swith on the screen, display "hello", beep
      result = 0; // and do other things that calculator do nowadays
   }

   public void switchOff()
   { }// Display "bye bye", beep, switch off the screen

   public int getResult()
   {
      return result;
   }
}