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

public class RPN2 extends Applet implements ActionListener
{
	Button one, two, three, four, five, six, seven, eight, nine, zero;   //declare the buttons, and numerous variables
	Button enterButton, addButton, divButton, subButton, multButton, clrButton; // and the panels I used to pretty things
	int numberFlag, errFlag, opFlag, TogOpFlag = 1, enterFlag;//up.  A lot of variables aren't used much, however
	double reg1, reg2, temp1, temp2;
	TextField value1; // but are their to help extend the program later one, ie, multiple registers
	Label Prompt1;
	String s1 = "";
	Panel p1 = new Panel(); // da panels
	Panel p2 = new Panel();
	Panel p3 = new Panel();
	Panel p4 = new Panel();
	Panel p5 = new Panel();


	public void init() // now display the buttons and stuff, as well as set up the OS to look out for button presses.
	{
		Prompt1 = new Label("Result");
		p1.add (Prompt1);
		value1 = new TextField(30);
		value1.setEditable(false);
		p1.add (value1);
		
		one = new Button("1");
		p2.add (one);
		one.addActionListener(this);
		
		two = new Button("2");
		p2.add (two);
		two.addActionListener(this);
		
		three = new Button("3");
		p2.add (three);
		three.addActionListener(this);
		
		addButton = new Button("+");
		p2.add (addButton);
		addButton.addActionListener(this);
		
		four = new Button("4");
		p3.add (four);
		four.addActionListener(this);
		
		five = new Button("5");
		p3.add (five);
		five.addActionListener(this);
		
		six = new Button("6");
		p3.add (six);
		six.addActionListener(this);
		
		subButton = new Button("-");
		subButton.addActionListener(this);
		p3.add (subButton);
		
		seven = new Button("7");
		p4.add (seven);
		seven.addActionListener(this);
		
		eight = new Button("8");
		p4.add (eight);
		eight.addActionListener(this);
		
		nine = new Button("9");
		p4.add (nine);
		nine.addActionListener(this);
		
		multButton = new Button("*");
		p4.add (multButton);
		multButton.addActionListener(this);
		
		clrButton = new Button("Clear");
		p5.add (clrButton);
		clrButton.addActionListener(this);
		
		zero = new Button("0");
		p5.add (zero);
		zero.addActionListener(this);
		
		enterButton = new Button("ENTER");
		p5.add (enterButton);
		enterButton.addActionListener(this);
		
		divButton = new Button("/");
		p5.add (divButton);
		divButton.addActionListener(this);
		
		add (p1);
		add (p2);
		add (p3);
		add (p4);
		add (p5);
	}
	
	public void actionPerformed (ActionEvent event)
	
	{
		if (event.getSource() == addButton) { //now when the operation buttons are presses (+, -, / ,*), it sets an opFlag variable to a value unique to that operation.
			if (opFlag == 1) {
				TogOpFlag++;
			}
			if (TogOpFlag != 1) {
				errFlag = 1;
			}
			opFlag = 1;
			repaint();
		} else
		if (event.getSource() == subButton) {
			if (opFlag == 2) {
				TogOpFlag++;
			}
			if (TogOpFlag != 1) {
				errFlag = 1;
			}
			opFlag = 2;
			repaint();
		} else 
		if (event.getSource() == divButton) {
			if (opFlag == 3) {
				TogOpFlag++;
			}
			if (TogOpFlag != 1) {
				errFlag = 1;
			}
			opFlag = 3;
			repaint();
		} else
		if (event.getSource() == multButton) {
			if (opFlag == 4) {
				TogOpFlag++;
			}
			if (TogOpFlag != 1) {
				errFlag = 1;
			}
			opFlag = 4;
			repaint();
		} else
		if (event.getSource() == clrButton) {
			opFlag = 5;
			repaint();
		} else
		if (event.getSource() == enterButton) { //if the enter button is pressed, we have to swap the register values around, and then zero reg1.
			enterFlag = 1;
			reg2 = reg1;
			reg1 = 0;
			s1 = "";
			repaint();
		} else
		if (event.getSource() == one) { //so that I can display the number that is pressed
			s1 = s1 + "1"; 				// I store what numbers have been pressed into a string
			repaint();					// so that I can easily have long numbers
		} else							//then I simply convert the string to a integer, ready for use.
		if (event.getSource() == two) {
			s1 = s1 + "2"; 
			repaint();
		} else
		if (event.getSource() == three) {
			s1 = s1 + "3";
			repaint();
		} else
		if (event.getSource() == four) {
			s1 = s1 + "4";
			repaint();
		} else 
		if (event.getSource() == five) {
			s1 = s1 + "5";
			repaint();
		} else
		if (event.getSource() == six) {
			s1 = s1 + "6";
			repaint();
		}  else
		if (event.getSource() == seven) {
			s1 = s1 + "7";
			repaint();
		} else
		if (event.getSource() == eight) {
			s1 = s1 + "8";
			repaint();
		} else
		if (event.getSource() == nine) {
			s1 = s1 + "9";
			repaint();
		} else
		if (event.getSource() == zero) {
			s1 = s1 + "0";
			repaint();
		}
	}
			
	public void paint (Graphics g)
	{
		  
		
		reg1 = Double.valueOf(s1).doubleValue();	//this is where the string is converted to a double and stored in the reg1, which was zeroed before
		value1.setText(s1);				// and then the string s1 is displayed in the TextField, so the user knows what they have entered.
		if (errFlag == 1) {
			value1.setText("Only press an operation Flag once, dumb, dumb!");
			}  else
		if (opFlag == 1) {
			temp2 = reg2 + reg1;
			s1 = Double.toString(temp2); //then the result is shown in the Textfield after the calculation
			value1.setText(s1);
			reg2 = 0;
		} else
		if (opFlag == 2) {
			temp2 = reg2 - reg1;
			s1 = Double.toString(temp2);
			value1.setText(s1);
			reg2 = 0;
		} else
		if (opFlag == 3) {
			temp2 = reg2 / reg1;
			s1 = Double.toString(temp2);
			value1.setText(s1);
			reg2 = 0;
		} else
		if (opFlag == 4) {
			temp2 = reg2 * reg1;
			s1 = Double.toString(temp2);
			value1.setText(s1);
			reg2 = 0;
		} else
		if (opFlag == 5) {  //when the clear function is pressed, then reset all the flags and variables and textfields.
			temp1 = 0;
			temp2 = 0;
			reg1 = 0;
			reg2 = 0;
			opFlag = 0;
			
			TogOpFlag = 1;
			errFlag = 0;
			s1 = "";
			value1.setText("");
			repaint();
		}
		
	}
}