how to display the listbox selected value into textbox

private void productlist_Load(object sender, EventArgs e)
        {
            con.Open();
            SqlCommand cmd = new SqlCommand("select productcode,productname from products", con);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds);            
           
            
            for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
            {
               
                listBox1.Items.Add(ds.Tables[0].Rows[i][0].ToString() + "\t\t" + ds.Tables[0].Rows[i][1].ToString());


            }
            
            con.Close();

        }