private void Mark_Attendence_Load(object sender, EventArgs e)
 {
     lblClass.Text = t.ClassName;
     AttendanceWS.AttendanceWebService aws = new PakTurk_school_system.AttendanceWS.AttendanceWebService();
     s = aws.displayStudentsBLL(lblClass.Text);
     listStudents.Visible = true;
     for (int i = 0; i < s.Tables[0].Rows.Count; i++)
     {
         listStudents.Items.Add(s.Tables[0].Rows[i][0]);
     }
 }
        private void dt_ValueChanged(object sender, EventArgs e)
        {
            AttendanceWS.AttendanceWebService aws = new PakTurk_school_system.AttendanceWS.AttendanceWebService();

            s.Clear();
            s = aws.displayStudentsBLL(lblClass.Text);
            listStudents.Items.Clear();


            for (int i = 0; i < s.Tables[0].Rows.Count; i++)
            {
                listStudents.Items.Add(s.Tables[0].Rows[i][0]);
            }
        }