private void btnLogin_Click(object sender, EventArgs e)
        {
            String username = txtUsername.Text.Trim();
            string password = txtPassword.Text.Trim();

            LoginBLL login = new LoginBLL();

            login._Username = username;
            login._Password = password;

            UsernameBLL._Username = txtUsername.Text;
            bool isValidUser = login.checkUser();

            if (isValidUser)
            {
                MessageBox.Show("Welcome");
                this.Hide();
                Pie_Chart pie = new Pie_Chart();
                pie.ShowDialog();

                this.Hide();
                DashBoard dashboard = new DashBoard();
                dashboard.ShowDialog();
                this.Close();
            }
            else
            {
                MessageBox.Show("Invalid Username or Password");
                txtPassword.Text = "";
                txtUsername.Focus();
                txtUsername.SelectAll();
            }
        }
        private void pieChartToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Pie_Chart piechart = new Pie_Chart();

            piechart.ShowDialog();
        }