private void btnPrevious_Click(object sender, EventArgs e)
        {
            this.Hide();
            subject s1 = new subject();

            s1.Show();
        }
 private void btn_sign_in_Click(object sender, EventArgs e)
 {
     try
     {
         if (txt_username.Text.Trim() != "" && txt_password.Text.Trim() != "")
         {
             DataTable dt = new DataTable();
             cmd = new SqlCommand("select user_name , user_password from user_registration where user_name=@user and user_password=@password", con);
             con.Open();
             cmd.Parameters.AddWithValue("@user", txt_username.Text.Trim());
             cmd.Parameters.AddWithValue("@password", txt_password.Text.Trim());
             adapt = new SqlDataAdapter(cmd);
             DataSet ds = new DataSet();
             adapt.Fill(ds);
             con.Close();
             int count = ds.Tables[0].Rows.Count;
             if (count == 1)
             {
                 MessageBox.Show("Welcome " + txt_username.Text.Trim());
                 Login_info.user_name = txt_username.Text.Trim();
                 this.Hide();
                 subject s1 = new subject();
                 s1.Show();
             }
             else
             {
                 MessageBox.Show("Invalid User Name Or Password !! ");
             }
         }
         else
         {
             MessageBox.Show("Please Provide Login Details");
         }
     }
     catch (Exception)
     {
         throw;
     }
 }