import java.awt.*;
import java.awt.event.*;
import javax.swing.JLabel;


//=============
// Calculator
//=============

//Declaring that we are interested in using the action listener
//Extends frame - inherits
public class Calculator extends Frame implements ActionListener, WindowListener
{
    private TextField display;
    private TextField status;
    private Engine engine = new Engine();

    public static void main( String[] args )
    {
        Frame f = new Calculator();
        f.setSize( 200, 300 );
        f.setLocation( 300, 150 );
        f.setTitle( "Calculator" );
        f.show();
    }
  
    public Calculator()
    {
        addWindowListener( this );
      
      // Adding the display for the calculator
      display = new TextField( "" );
        display.setEditable( false );    
      add( display, "North" );
              
      //New panel specifying grid for all the numbers and functions
        Panel p = new Panel();
      p.setLayout( new GridLayout( 5, 4, 5, 4 ) );
      //p.setVgap ( 1, 1 ); THIS IS NOT WORKING

      //Adding the buttons
      p.add(new JLabel(""));
      p.add(new JLabel(""));
      p.add(new JLabel(""));
      addButton( p, "CE" );
      addButton( p, "CA" );
      addButton ( p, "7" );
      addButton ( p, "8" );
      addButton ( p, "9" );
      addButton ( p, "/" );
      addButton( p, "M+" );
      addButton ( p, "4" );
      addButton ( p, "5" );
      addButton ( p, "6" );
      addButton ( p, "*" );
      addButton ( p, "MC" );
      addButton ( p, "1" );      
      addButton ( p, "2" );
      addButton ( p, "3" );
        addButton( p, "-" );
      addButton( p, "MRC" );
      addButton ( p, "0" );
      addButton ( p, "%" );
        addButton( p, "." );
        addButton( p, "+" );
        addButton( p, "=" );

        add( p, "Center" );
      
      //this is to add a textfield panel at the bottom
        status = new TextField();
        status.setEditable( false );
        status.setText("Welcome to my calculator");
        add( status, "South" );
   }

    public void addButton( Container c, String s )
    {
        Button b = new Button( s );
        c.add( b );
        b.addActionListener( this );
    }

    public void actionPerformed( ActionEvent evt )
       //Handling graphic user interface events
      {
        String s = evt.getActionCommand();
        int result;

//To try and limit the length of the textfield to 8      
//      if ( engine.started() )
//      display.setText( s );
//    else {
//          String str = display.getText();
//          if(str.length() < 8)
//                 display.setText( str + s );
//          }
//        engine.stop();
//        }

           if ( '0' <= s.charAt( 0 ) && s.charAt( 0 ) <= '9' )
           {
           
         if ( engine.started() )
                   display.setText( s );
               else
                   display.setText( display.getText() + s );
               engine.stop();
           }
        
         else
           {
               result = engine.calculate( Integer.parseInt( display.getText() ) );
               display.setText( "" + result );
               engine.operation( s );
               engine.start();
           }
[b]            
         if (s == " CA ")
         {
            display.setText( "0" );
            }
[/b]     
         //else if
         //{
         //(s == " M+ ")
         //{
         //  
         //}
         //
         //}
      }  

    public void windowActivated(WindowEvent e)
    {
        return;
    }

    public void windowClosed(WindowEvent e)
    {
        return;
    }

    //Close the window using windows listener to close the calculator
   public void windowClosing(WindowEvent e)
    {
        dispose();
    }

    public void windowDeactivated(WindowEvent e)
    {
        return;
    }

    public void windowDeiconified(WindowEvent e)
    {
        return;
    }

    public void windowIconified(WindowEvent e)
    {
        return;
    }

    public void windowOpened(WindowEvent e)
    {
        return;
    }
}

public class Engine
{
    private int acc = 0;
    private String op = "=";
    public boolean start = true;

    public Engine()
    {
    }

    public void start()
    {
        start = true;
    }

    public void stop()
    {
        start = false;
    }

    public boolean started()
    {
        return start;
    }

    public void operation( String op )
    {
        this.op = op;
    }

    public int calculate( int n )
    {
        if ( op.equals( "+" ) )
            acc += n;
        else if ( op.equals( "-" ) )
            acc -= n;
        else if ( op.equals( "*" ) )
            acc *= n;
        else if ( op.equals( "/" ) )
            acc /= n;
        else if ( op.equals( "%" ) )
            acc %= n;
        else if ( op.equals( "=" ) )
            acc = n;
      else if ( op.equals( "CE" ) )
         acc = 0;
      else if ( op.equals( "CA" ) )
          acc = 0;
      //else if ( op.equals( "M+" ) )
      //   acc = n;
      //else if ( op.equals( "MC" ) )
      //   acc = n;
      //else if ( op.equals( "MRC" ) )
      //   acc = n;

        return acc;
    }
}

         if (s.equals( "CA" ) )
         {
            if ( engine.started() )
              
               display.setText ( "0" );
               else
                  status.setText( "All Cleared" );
                  engine.stop();
         }