private void checkBox1_CheckedChanged(object sender, EventArgs e) { double Height, Weight; if (checkBox1.Checked) { if (double.TryParse(txtPatHeight.Text, out Height) == true && double.TryParse(txtPatWeight.Text, out Weight) == true) { txtpatBMI.Text = string.Format("{0:n2}", selectClass.calBMI(Convert.ToDouble(txtPatHeight.Text), Convert.ToDouble(txtPatWeight.Text)).ToString()); } else { checkBox1.CheckState = 0; MessageBox.Show("Either Height or Weight value is not numeric" + Environment.NewLine + "Please check the values", "Error - Onana HMS", MessageBoxButtons.OK, MessageBoxIcon.Exclamation); } } else if (!checkBox1.Checked) { txtpatBMI.Text = ""; } }