private void Item_Click(object sender, EventArgs e) { Button btn = (Button)sender; string display = this.txtDisplay.Text; try { if (!string.IsNullOrEmpty(display) && !display.StartsWith(".")) { FormValue = double.Parse(display); } } catch (Exception ex) { FormValue = 0; } switch (btn.Tag.ToString()) { case "1": case "2": case "3": case "4": case "5": case "6": case "7": case "8": case "9": case "0": display += btn.Tag.ToString(); break; case ".": if (!display.Contains(".")) { display += "."; } break; case "+1": FormValue += 1; display = FormValue.ToString(); break; case "+10": FormValue += 10; display = FormValue.ToString(); break; case "+100": FormValue += 100; display = FormValue.ToString(); break; case "-1": FormValue -= 1; display = FormValue.ToString(); break; case "-10": FormValue -= 10; display = FormValue.ToString(); break; case "-100": FormValue -= 100; display = FormValue.ToString(); break; case "+/-": FormValue = FormValue * -1; display = FormValue.ToString(); break; case "Back": if (display.Length > 0) { display = display.Substring(0, display.Length - 1); } break; case "C": display = ""; break; default: break; } this.txtDisplay.Text = display; //Set FormValue if (!string.IsNullOrEmpty(display) && !display.StartsWith(".")) { FormValue = double.Parse(display); } }