how to convert the Nvarchar to Integer with Select c#

Question

please help me  and look to this code

string mainconn = ConfigurationManager.ConnectionStrings["Con_VisitorsControl"].ConnectionString;
SqlConnection sqlconn = new SqlConnection(mainconn);
string sqlquery = "select VisitorName, IqamaCopy from [dbo].[tbl_Visitors] where VisitorId = ' " + txtno.Text + " ' ";
SqlCommand sqlcomm = new SqlCommand(sqlquery, sqlconn);
sqlconn.Open();
SqlDataAdapter sda = new SqlDataAdapter();
sda.SelectCommand = sqlcomm;
DataSet ds = new DataSet();
sda.Fill(ds);
DataList1.DataSource = ds;
DataList1.DataBind();
sqlconn.Close();

this VisitorId Is Nvarchar contain to 9 digits on sql how can i select and convert this fieldname in the c#

 

thanks