在C＃中的数据库连接字符串问题:

 private void button1_Click(object sender, EventArgs e)

        {

            con = new SqlConnection();

            string q = "Data Source=TOSHIBA-PC;Initial Catalog=ACCESSCONTROL;User ID=ABC;Password=hello;MultipleActiveResultSets=True";

            cmd = new SqlCommand (q,con);

            

            try

            {

                con.Open();

                MessageBox.Show("Connection opened.");

            }

            catch (SyntaxErrorException a)

            {

                MessageBox.Show("Error: " + a);

            }

            finally

            {

                con.Close();

                MessageBox.Show("Connection closed.");

            }

      

        }

错误:ConnectionString属性尚未初始化。