private void button3_Click(object sender, EventArgs e)
        {
            listele = new Listele();
            SqlConnection con = new SqlConnection(conString);
            string        sorgu;

            sorgu = " Delete from Users where UseId = '" + textBox9.Text + "' and UsName = '" + textBox10.Text + "'";
            listele.DbSil(sorgu);
            MessageBox.Show(textBox9.Text + ",  " + textBox10.Text + " kişi silindi");
            textBox9.Text  = "";
            textBox10.Text = "";
        }
        private void button2_Click(object sender, EventArgs e)
        {
            listele = new Listele();
            SqlConnection con = new SqlConnection(conString);
            string        sorgu;

            sorgu = " Delete from Books where ISBN = '" + textBox6.Text + "' and BookTitle = '" + textBox7.Text + "' and Publisher='" + textBox8.Text + "'";
            listele.DbSil(sorgu);
            MessageBox.Show(textBox6.Text + ",  " + textBox7.Text + ", " + textBox8.Text + " kitabı silindi");
            textBox6.Text = "";
            textBox7.Text = "";
            textBox8.Text = "";
        }