C#

private void Form1_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
		{
			//Read file and Draw ellipse around points
			if (!isMouseDown)
			{
				using (sr = new StreamReader("DataPoints.txt"))
				{
					string str = sr.ReadLine();
					if (str == null)
						return;
					string [] strs = str.Split(' ');
					if (strs.Length != 2)
						return;
					Point pt1 = new Point(int.Parse(strs[0]),int.Parse(strs[1]));

 			 

					Graphics g = e.Graphics;
					while ((str = sr.ReadLine()) != null)
					{
						strs = str.Split(' ');
						if (strs.Length != 2)
							break;
						Point pt2 = new Point(int.Parse(strs[0]),int.Parse(strs[1]));							
							 
						g.DrawEllipse(Pens.Blue, pt2.X-2, pt2.Y-2, 4, 4);
						g.DrawLine(Pens.Black, pt1, pt2);
						pt1 = pt2;
							 
					}
				}
				 
			}
		}

		private void Form1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
		{
			if (line)
			{
				isMouseDown = true;
				pt1 = new Point(e.X, e.Y);
				point = pt1;				

				//Open file 
				sw = new StreamWriter("DataPoints.txt");
								 
			}

			if (eraser)
			{				
				//Eraser
				pt.X = e.X;
				pt.Y = e.Y;
				g.FillRectangle(bgBrush, pt.X-10, pt.Y-10, 20, 20);
				g.DrawRectangle(Pens.Red, pt.X-10, pt.Y-10, 20, 20);
			}
		}

		private void Form1_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
		{
			if (line)
			{
			
				if (isMouseDown)
				{
					pointArray.Add("nvcls");
					pointArray.Add("Eric");

					pt2 = new Point(e.X, e.Y);
					Graphics g = this.CreateGraphics();
					g.DrawLine(pen, point, pt2);
					tempG.DrawLine(pen, point, pt2);
					point = pt2;


					ptCount = point;
					AddPoint(ptCount);

					//this.Refresh();					 
					 				
				}
			}


			if (eraser)
			{
				if (isMouseDown)
				{
					line = false;

					//Eraser
					g.FillRectangle(bgBrush,e.X-10,e.Y-10,20,20);
					g.DrawRectangle(Pens.Red,e.X-10,e.Y-10,20,20);
					//Erase area
					g.DrawRectangle(new Pen(this.BackColor),pt.X-10, pt.Y-10, 20, 20);
						
					pt.X = e.X;
					pt.Y = e.Y;

					RemovePoint(ptCount);	
				}
			}
		}

		private void Form1_MouseUp(object sender, System.Windows.Forms.MouseEventArgs e)
		{
			if (line)
			{
				isMouseDown = false;
			
				//tempG.DrawLine(pen, pt1, pt2);
				this.BackgroundImage = (Bitmap) tempImage.Clone();

				//write points to file 
				//				sw.WriteLine(e.X + " " + e.Y);

				sw.Close();

				this.Refresh();
			}			 
			
		}


		private void Form1_Resize(object sender,System.EventArgs e)
		{
			this.BackgroundImage = (Bitmap) tempImage.Clone();
		}
    

	 
		private void toolBar1_ButtonClick(object sender, System.Windows.Forms.ToolBarButtonClickEventArgs e)
		{
			if ( e.Button == tbPolygon)
				line = true;
			else if (e.Button == tbEraser)
			{
				//				line = false;
				eraser = true;
			}
			else if (e.Button == tbSave) 
				Save();

		}



		public void AddPoint(Point ptCount)
		{
			pointArray.Add(ptCount);
		}


		private static void RemovePoint(Point ptCount)
		{
			//Remove points from list
			for (int i = 0; i <= pointArray.Count; i ++)
			{
				bool isMatch = Object.Equals(pointArray[i], ptCount);
				if (isMatch)
					pointArray.Remove(pointArray[i]);
			}
		}


		private void Save()
		{
			//			sw = new StreamWriter("DataPoints.txt");
			foreach (string s in pointArray)
			{
				sw.WriteLine(s);
			}
			sw.Close();
		}