private void button1_Click(object sender, EventArgs e)
        {
            DataTable dt2 = db.select_questions(username.Text);

            foreach (DataRow dr in dt2.Rows)
            {
                if (dr[0].ToString() == comboBox1.SelectedItem.ToString() && dr[1].ToString() == textBox1.ToString())
                {
                    label1.Text    = "Password is " + dr[2].ToString();
                    label1.Visible = true;
                }
                else
                {
                    label1.Text    = "Something is wrong";
                    label1.Visible = true;
                }
            }
            this.Refresh();
        }