private void btnIDGenerate_Click(object sender, EventArgs e)
        {
            if (cbAutoID.Checked == true)
            {
                string szSQL = string.Format("SELECT CUSTID, FIRSTNAME, LASTNAME FROM CUSTOMERS");
                SqlConnection conn = DBProcess.DBConnection();
                conn.Open();
                SqlDataAdapter sda = new SqlDataAdapter(szSQL, conn);
                DataTable dt = new DataTable();
                sda.Fill(dt);
                conn.Close();

                var random = new Random();
                int randID = random.Next(100000, 999999);
                List<int> CustIDs = new List<int>();

                for (int i = 0; i < dt.Rows.Count; i++)
                {
                    while (randID == dt.Rows[i].Field<int>(0))
                    {
                        randID = random.Next(100000, 999999);
                    }
                }

                tbID.Text = randID.ToString();
            }
        }
        public DataTable GetData()
        {
            string        szSQL = string.Format("SELECT CUSTID, FIRSTNAME, LASTNAME FROM CUSTOMERS");
            SqlConnection conn  = DBProcess.DBConnection();

            conn.Open();
            SqlDataAdapter sda = new SqlDataAdapter(szSQL, conn);
            DataTable      dt  = new DataTable();

            sda.Fill(dt);
            conn.Close();

            dgvCustomers.Rows.Clear();
            return(dt);
        }
        private void btnCreateCust_Click(object sender, EventArgs e)
        {
            if (tbFirstName.Text != null && tbLastName.Text != null && tbID.Text.Length == 6)
            {
                string szSQL = string.Format("INSERT INTO CUSTOMERS VALUES (@FIRSTNAME, @LASTNAME, @CUSTID)");

                DBProcess.DBManipulate(szSQL, int.Parse(tbID.Text), tbFirstName.Text, tbLastName.Text);
                this.Close();
            }
            else if (tbFirstName.Text == "" && tbLastName.Text == "")
            {
                MessageBox.Show("Please enter first and last name.");
            }
            else if (tbID.Text.GetType() != typeof(int) && tbID.Text.Length != 6 && tbID.Text == null)
            {
                MessageBox.Show("Please enter correct ID.");
            }
            else
            {
                MessageBox.Show("Something is wrong.");
            }
        }