private void button2_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "")
            {
                errorProvider1.Clear();
                errorProvider1.SetError(textBox1, "Please Enter Serial Number");
            }
            else
            {
                errorProvider1.Clear();
                conn();
                cmd.CommandText = "Delete from Service where Serial=@sn";

                cmd.Parameters.AddWithValue("@sn", textBox1.Text);

                cmd.ExecuteNonQuery();

                DeleteDone dd = new DeleteDone();
                dd.Show();

                textBox1.Clear();
                textBox2.Clear();
                textBox3.Clear();
                textBox4.Clear();
                textBox5.Clear();
                textBox6.Clear();

                richTextBox2.Clear();
                richTextBox1.Clear();
            }
        }
        private void button2_Click(object sender, EventArgs e)
        {
            if (textBox2.Text == "")
            {
                errorProvider1.Clear();
                errorProvider1.SetError(textBox2, "Please Insert Customer Name");
            }
            else
            {
                errorProvider1.Clear();

                conn();
                cmd.CommandText = "Delete from Saleinv where Cname=@cname";

                cmd.Parameters.AddWithValue("@cname", textBox2.Text);

                cmd.ExecuteNonQuery();

                DeleteDone dd = new DeleteDone();
                dd.Show();

                textBox1.Clear();
                textBox2.Clear();
                textBox3.Clear();
                textBox5.Clear();
                textBox6.Clear();
                comboBox1.Text = "";
                comboBox2.Text = "";
                comboBox3.Text = "";
                comboBox4.Text = "";
            }
        }