//-------------------------------------------------------------------
// This program draws a mathematical graph by plotting single points.
// A continuous "curve" could be drawn by drawing lots of small
// line segments (connecting the dots).
//-------------------------------------------------------------------

import java.awt.*;

public class Parabola extends EasyApp
{   
   public static void main(String[] args)
   {  new Parabola(); }

   Button  bAdd = addButton("Change",420,40,60,30,this);

   double A = 1;
   double B = 0;
   double C = 0;

   public Parabola()
   {   setTitle("MathDraw");
       this.setSize(630,450);
       repaint();
   }

    public void actions(Object source,String command)
    {
       if (source == bAdd)
       {  A = inputDouble("A");
          B = inputDouble("B");
          C = inputDouble("C");
       }
       repaint();
    } 

    public void paint(Graphics g)
    {   
        grid(g);
        curve(g);
    }
    

    public void grid(Graphics g)
    {   
        g.setColor(Color.gray);
        for (int x = 0; x <=400; x = x + 20)
        {  
           g.drawLine(x,0,x,400);
        }
        for (int y = 0; y <=400; y = y + 20)
        {  
           g.drawLine(0,y,400,y);
        }
        g.setColor(Color.black);
        g.drawLine(200,0,200,400);
        g.drawLine(199,0,199,400);
        g.drawLine(0,199,400,199);
        g.drawLine(0,200,400,200);
    }
        
    public void curve(Graphics g)
    {
       g.setColor(Color.red);
       for (double x=-10;x<=10;x = x+0.1)
       {
         double y = A*x*x+B*x+C;
         int xp = (int)Math.round(200 + x*20);
         int yp = (int)Math.round(200 - y*20);
         g.fillOval(xp-2,yp-2,5,5);
          
       }
    }
}