private void btn_AdminReg_Click(object sender, EventArgs e)
{
    this.Hide();
    Admin_Login login = new Admin_Login(1);
    login.Show();
}

public partial class Admin_Login : MetroFramework.Forms.MetroForm
{
    int separator; // this is used to separate different logins

    public Admin_Login(int value)
    {
        InitializeComponent();
        separator = value;
    }

    //------- Legend ---------
    //if separator= 1 : AdminTerminal
    //if separator= 2 : UpdatingTerminal
    //if separator= 3 : View Registration
    //if separator= 4 : Registration
    //if separator= 5 : Reports
    //if separator= 6 : Cancel Union

    static string path = Path.GetFullPath(Environment.CurrentDirectory);
    static string dataBaseName = "Trade_Union_Registration.mdf";

    private void btn_Login_Click(object sender, EventArgs e)
    {
        if (separator == 1)
        {
            Data getTable = new Data();
            DataTable table = getTable.GetData("select  UserName,Password from SuperUser where UserName='" + txt_UserName.Text + "' and Password='" + txt_Password.Text + "'");

            if (table.Rows.Count == 1)
            {
                this.Hide();
                TerminalAdmin AdminTerminal = new TerminalAdmin();
                AdminTerminal.Show();
            }
            else
            {
                MetroFramework.MetroMessageBox.Show(this, "Invalid Username/Password please check your Username and Password and try again.", "Access Denied", MessageBoxButtons.OK, MessageBoxIcon.Error);
                txt_Password.Clear();
            }
        }
        else if (separator == 2)
        {
            Data getTable = new Data();
            DataTable table = getTable.GetData("select  UserName,Password from Admin_Table where UserName='" + txt_UserName.Text + "' and Password='" + txt_Password.Text + "'");

            if (table.Rows.Count == 1)
            {
                Data getter = new Data();
                DataTable dt = getter.GetData("select UserID from Admin_Table where UserName='" + txt_UserName.Text + "'");
                MessageBox.Show(dt.Rows[0][0].ToString());
                this.Hide();
                Updating form = new Updating(dt.Rows[0][0].ToString(), txt_UserName.Text);
                form.Show();
            }