Conditional User input Form

            switch (comboBox_Type.SelectedIndex)
            {
                case 0:     //Main Hub
                    GlobalClass.IP = "10.247.247.130";
                    NetworkSet();
                    break;
                case 1:     //Extension Hub
                    GlobalClass.IP = "10.247.247.150";
                    NetworkSet();
                    break;
                case 2:     //ALARM Module
                    GlobalClass.IP = "10.247.247.170";
                    NetworkSet();
                    break;
                case 3:     //NVR Module
                    GlobalClass.IP = "10.247.247.180";
                    NetworkSet();
                    break;
                case 4:     //Custom
                    GlobalClass.IP = "";
                    Form3 thirdForm = new Form3();
                    thirdForm.ShowDialog();
                    NetworkSet();
                    break;
                default:
                    break;
            }

        public void BtnOk_Click(object sender, EventArgs e)
        {
            string Errors = null;
            //&& IsAddressValid(NewSM.Text) == true && IsAddressValid(NewGW.Text) == true
            if (IsAddressValid(NewIP.Text) != true)
            {
                Errors += "INVALID IP ADDRESS\n";
            }
            if (IsAddressValid(NewSM.Text) != true)
            {
                Errors += "INVALID SUBMASK ADDRESS\n";
            }
            if (IsAddressValid(NewGW.Text) != true)
            {
                Errors += "INVALID GATEWAY ADDRESS\n";
            }
            if (string.IsNullOrEmpty(Errors))
            {

                GlobalClass.IP = NewIP.Text;
                GlobalClass.Mask = NewSM.Text;
                GlobalClass.Gateway = NewGW.Text;
                Close();
            }
            else {
                MessageBox.Show(Errors, "Error");
            }
        }

        private void BtnCnl_Click(object sender, EventArgs e) => Close();