import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.util.Stack;

public class ExpressionEval extends Applet
                            implements ActionListener {
   private Button[][] buttons;    // array of Button objects.
   private Label result = new Label();   // Label for result
   private Label infix = new Label();   // Label for expression
   private Label nextChar = new Label();  // Label for each char of expression
   private String infixStr = "";  // expression being evaluated
   protected Label operandLabel = new Label();  // Label for operand stack
   protected Label operatorLabel = new Label(); // Label for operator stack

   Calculator calc = new Calculator();  // Calculator object

   public void init() {
       Label instruct = new Label("Press = to end expression");
       add(instruct);
       Panel map = new Panel();    // a panel in our applet
       // characters to be used as button labels.
       char [][] opMap = { {'0', '1', '2'},
                           {'3', '4', '5'},
                           {'6', '7', '8'},
                           {'9', ' ', '='},
                           {'*', '/', '+'},
                           {'-', '(', ')'} };

    // Create an array of buttons of the proper dimensions.
    buttons = new Button[opMap.length][opMap[0].length];

    // Create the 6 x 3 grid of buttons
    map.setLayout(new GridLayout(buttons.length, buttons[0].length));

    // Create and label each button, add it to applet,
    //   and register applet as listener.
    for (int r = 0; r < buttons.length; r++)
       for (int c = 0; c < buttons[r].length; c++) {
             // create labelled button - take label from array opMap
             buttons[r][c] = new Button("" + opMap[r][c]);
             map.add(buttons[r][c]);              // add to panel
             buttons[r][c].addActionListener(this);
       }
    add(map);
    nextChar.setText("________________________________________");
    add(nextChar);
    infix.setText("________________________________________");
    add(infix);
    operandLabel.setText("___________________________________________");
    add(operandLabel);
    operatorLabel.setText("___________________________________________");
    add(operatorLabel);
    result.setText("___________________________________________");
    add(result);

    // add reset button



} // init

   public void clear() {





   }

   public void actionPerformed(ActionEvent e) {
      Button b = (Button)e.getSource(); // Gets the button pressed,
      if (b == reset) {


         return;
      }

      char token = (b.getLabel()).charAt(0); // token is label character
      infixStr = infixStr + token;       // Append it to expression
      nextChar.setText("Character is " + token);
      infix.setText("Expression so far: " + infixStr);

      // Process the token
      if (token >= '0' && token <= '9')
        calc.processDigit(token);
      else {
        String message = calc.processOperator(token, this);
        result.setText(message);
      }
   }
}