import java.awt.*;
import java.applet.Applet;
import java.awt.event.*;

public class Calculator extends Applet implements ActionListener
{
    private TextField display;
    private int argument;
    private String operation = "=";
    private boolean start;

    public void init()
    {
        display = new TextField("0",10);
        display.setEditable(false);
        add(display);

        for (int i = 0; i <=9; i++)
        {
            createButton(Integer.toString(i));
        }

        createButton("+");
        createButton("-");
        createButton("*");
        createButton("/");
        createButton("=");
    }

    public void createButton(String label)
    {
        Button button = new Button(label);
        add(button);
        button.addActionListener(this);
    }

     public void actionPerformed(ActionEvent event)
     {
         String s = ((Button)event.getSource()).getLabel();

         if('0' <=s.charAt(0) && s.charAt(0) <='9')
         {
            if (start) display.setText(s);
            else display.setText(display.getText()+s);
            start = false;
     }

     else
     {
        if (start)
        {
           if (s.equals("-"))
           {
              display.setText(s);
              start = false;
           }

           else operation = s;
        }

        else
        {
           calculate(Integer.parseInt(display.getText()));
           operation = s;
           start = true;
        }
     }
  }

  public void calculate(int n)
  {
      if (operation.equals("+")) argument = argument+n;
      else if (operation.equals("-")) argument = argument-n;
      else if (operation.equals("*")) argument = argument*n;
      else if (operation.equals("/")) argument = argument/n;
      else if (operation.equals("=")) argument = argument=n;
      display.setText(""+argument);
  }
}