private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
 {
     x = "stu";
     z = comboBox1.Text;
     textBox3.Visible  = true;
     textBox3.ReadOnly = true;
     textBox3.Text     = z;
     textBox4.Visible  = false;
     textBox5.Visible  = false;
     label6.Visible    = false;
     label4.Visible    = true;
     label5.Visible    = false;
     label4.Text       = "Stage";
     label3.Text       = "Id";
     dt.Clear();
     if (z != null)
     {
         dt = stu.get(z);
     }
     dataGridView1.DataSource = dt;
     textBox1.Text            = " ";
     textBox2.Text            = " ";
     textBox3.Text            = " ";
     textBox4.Text            = " ";
     textBox5.Text            = " ";
 }
 public lectures(string prf, string lec, string Stage, string end)
 {
     prname  = prf;
     lecname = lec;
     stage   = Stage;
     END     = end;
     InitializeComponent();
     timer2.Start();
     closeToolStripMenuItem.Enabled       = false;
     activateToolStripMenuItem.Enabled    = false;
     allStudentsToolStripMenuItem.Enabled = false;
     // axAcroPDF1.Visible = false;
     dt.Clear();
     if (stage != null)
     {
         dt = s.get(stage);
         dataGridView1.DataSource = dt;
     }
     dt2.Clear();
     dt2.Columns.Add("Name", typeof(string));
     dt2.Columns.Add("Id", typeof(string));
     dt2.Columns.Add("Stage", typeof(string));
 }