import java.awt.*;

public class Pocket extends Frame
{
   TextField t;
   Button h[] = new Button[16];
   int accumulator = 0;
   boolean start = true;
   int op = 0; 

   public Pocket ()
   {
      setTitle("Pocket Calculator");
      add("North", t = new TextField());
      t.setEditable(false);
      Panel p = new Panel();
      p.setLayout(new GridLayout(4,4));
      for (int i=0 ; i < 10 ; i++)
         p.add(h[i] = new Button(String.valueOf(i)));
      p.add(h[10] = new Button("+"));
      p.add(h[11] = new Button("-"));
      p.add(h[12] = new Button("="));
      p.add(h[13] = new Button("+/-"));
      p.add(h[14] = new Button("*"));
      p.add(h[15] = new Button("/"));
      add("Center",p);
   }

   public boolean action (Event evt, Object obj)
   {
      int input;

      for (int i=0 ; i < 10 ; i++)    // A digit button is pressed
      {
         if (evt.target.equals(h[i]))
	 {
            if (start) { start = false; t.setText(""); }
            t.setText(t.getText() + String.valueOf(i));
            return super.action(evt, obj);
	 }
      }

      if (evt.target.equals(h[13]))   // The +/- button is pressed
         t.setText(String.valueOf(-Integer.parseInt(t.getText())));

      else     // Some operation is requested (+,-,*,/,=)
      {
         for (int i=10 ; i < 16 ; i++)
	 {
            if (evt.target.equals(h[i]))
            {
               start = true;
               if (t.getText().equals("")) input = 0;
               else
                  input = Integer.parseInt(t.getText());
               switch (op) {
               case 10: accumulator += input; break;
               case 11: accumulator -= input; break;
               case 14: accumulator *= input; break;
               case 15: accumulator /= input; break;
               default:
                  if (t.getText().equals("")) accumulator = 0;
                  else accumulator = Integer.parseInt(t.getText());
	       }
               op = i;
               if (op == 12) t.setText(String.valueOf(accumulator));
            }
	 }
      }
      return super.action(evt, obj);
   }

   public static void main (String arg[])
   {
      Pocket calculator = new Pocket();
      calculator.resize(200,240);
      calculator.show();
   }
}