Please try below code ...
SqlDataAdapter da4 = new SqlDataAdapter("select rate_km,rate_day from vehicle_category where vehicle_name='" + ddlvnameri.SelectedValue +"' and vehicle_type='"+ ddlvtype.SelectedValue +"' ",con);
DataTable dt4 = new DataTable();
DataRow[] dr;
Note: You cann't use '
&&' operator in Sql queries, instead use '
and' operator..
Also for '
||' operations use '
OR' operator..