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

public class PiSimple extends Applet implements ActionListener {

TextField tf;
double piOverFour;
int attempts;
Label instructions, colorChange;

public void init() 
{
	attempts = 0;
	instructions = new Label("Type number up to a billion and click enter");
	add(instructions);
	tf = new TextField(9);
	add(tf);
	tf.addActionListener(this);
	colorChange = new Label("Color will change when calculation finished");
	add(colorChange);
}

public void paint(Graphics g)
{
	g.drawString("Approximation of pi = " + String.valueOf(4.0*piOverFour), 10 , 100);
	g.drawString("Actual first dig of pi  = 3.14159265358979323846264338....", 10 , 120);
}

static final int getIntFromString(String s)
{
	s = s.trim();
	if (s.equals("") || s == null) return (1);
	try
	{
		return (Integer.valueOf(s).intValue());
	}
	catch (Exception e)
	{
		return(1);
	}
}

public void actionPerformed (ActionEvent e)
{
	attempts++;
	int terms = getIntFromString(tf.getText());
	if (terms > 1000000000) terms = 1000000000;
	piOverFour = 0.0;
	for (int i=0; i<terms; i++)
	{// implements formula pi/4 = 1 -1/3 + 1/5 -1/7 + 1/9 .....
		if (i%2 == 0) piOverFour += 1.0/((double)(2*i + 1));
		else piOverFour -= 1.0/((double)(2*i + 1));
	}
	Color color = new Color(225, 225 - ((attempts%2)*30), 255);
	setBackground(color);
	instructions.setBackground(color);
	colorChange.setBackground(color);
	repaint();
}
}  // END OF Class PiSimple