/*
	Add
	===
	Author Chris Pollett
	Course:  CSCI 102 Clark University
	Date: Feb. 8

	Purpose: This applet allows the user to enter two arbitrarily long
	======== numbers in textfields and see their sum printed out after a 
		 submit button is pressed.
	
	How to Use:
	===========
	javac Add.java
	
	appletviewer Add.class

	Methods:
	========
	public void init() -- overrides Applet init() to initialise background,
		textfields, buttons, and listeners.
		
	public void actionPerformed(ActionEvent e) -- handles events generated
			 by submit button. Adds two textfields

	private Vector rev(String s) -- takes a strings and enters it
				character by character in reverse order into
				a vector	
	
*/
	  
import java.util.*;
import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
import java.awt.Font;


public class Add extends Applet implements ActionListener {
	private Font font;
	private Label l1,l2, blank, output,name; 
	private TextField t1,t2;	
	private Button b;

	public void init()
	{//post: background colour set and listeners and GUI components added


		//
		//set background and layout
		//
		setBackground(new Color(00,255,255)); //background is cyan
		font = new Font ("SansSerif",Font.BOLD,18);
		setLayout( new GridLayout( 4,2));		
		
		//
		//now we add the Label's and TextField's
		//

		name= new Label("Add Applet");
		name.setFont(font);
		add(name);

		blank = new Label(""); //blank label to keep GridLayout
		add(blank);		//happy

		l1 = new Label("Number 1:");
		add(l1);
		
		t1 = new TextField("0",20);
		add(t1);
	
		l2 = new Label("Number 2:");
		add(l2);
		
		t2 = new TextField("0",20);
		add(t2);
				
		b = new Button("Click for the sum:");
		b.addActionListener(this);				
		add(b);

		output = new Label("0");
		add(output);		
	}

	public void actionPerformed(ActionEvent e)
	{ //post: sum of two inputs printed to applet

		Vector v1 = rev(t1.getText()); //convert text in t1 to a Vector
		Vector v2 = rev(t2.getText()); //convert text in t2 to a Vector
		int carry=0;
		int max,i, e1,e2;
 		Vector vsum;
		StringBuffer b;

		max = Math.max(v1.size(),v2.size());

		vsum =new Vector();	

		//add the two vectors
		for(i=0; i<max; i++)
		{
			e1 = (i< v1.size() ? Integer.valueOf(v1.elementAt(i).toString()).intValue(): 0);
			e2 = (i< v2.size() ? Integer.valueOf(v2.elementAt(i).toString()).intValue(): 0);
 
			vsum.addElement(new Integer((e1+e2+carry)%10));
			carry = (e1+e2+carry)/10;
		}

		if(carry != 0) vsum.addElement(new Integer(carry));
		
		//copy the result to a string buffer
		b =new StringBuffer();

		for( i = vsum.size()-1; i>=0; i--)
			{b.append(vsum.elementAt(i));}
	
		//output the result
		output.setText(b.toString());
	}

	private Vector rev (String s)
		{ //post: add each character of s in reverse order into
			a vector which is then returned

		  Vector v;
		  v =new Vector();
		  for (int i=s.length()-1; i >=0 ; i--)
			{v.addElement(new Integer(Character.digit(s.charAt(i),10)));}
		  return v;
		}

	
}