Add Item in List using Lookup Column

I have a list named "Designation" that contains a Designation Code and Designation Name. I have another list named "Employee" that contains Employee Name and Designation Name (as a Lookup Field). I am able to insert values to "Employee" list using the following code.     protected void AddEmp(object sender, EventArgs e)     {       string emp_name = txtEmployeeName.Text;       string emp_designation = ddlDesignation.SelectedValue;                           using (SPSite site = new SPSite("My Site"))       {        using (SPWeb web = site.OpenWeb())        {         SPSecurity.RunWithElevatedPrivileges(delegate()         {          web.AllowUnsafeUpdates = true;          SPList splist_employees = web.Lists["Employee"];          SPList splist_designations = web.Lists["Designations"];          SPListItemCollection splc_items = splist_employees.Items;          SPListItem spli_item = splc_items.Add();          SPFieldLookup lookup = splist_employees.Fields["Designated"] as SPFieldLookup;          string fieldName = lookup.LookupField;          spli_item["Employee Name"] = emp_name;          spli_item[fieldName] = GetLookFieldIDS(emp_designation, splist_designations);          spli_item.Update();        });       }       }     }     public static string GetLookFieldIDS(string lookupValues, SPList lookupSourceList)     {      string id = string.Empty;      SPFieldLookupValueCollection lookupIds = new SPFieldLookupValueCollection();      SPQuery query = new Microsoft.SharePoint.SPQuery();      query.Query = "<Where><Eq><FieldRef Name='Designation' /><Value type='Text'>"+lookupValues + "</Value></Eq></Where>";      SPListItemCollection listItems = lookupSourceList.GetItems(query);      foreach (Microsoft.SharePoint.SPListItem item in listItems)      {       id = item.ID.ToString();      }      return id;     } Here I have given the field name as 'Designation' inside the query. But, I want to find the field name based on the value given from the user end instead of hard-coding the field name as 'Designation'. Any help is greatly appreciated. Thanks in advance.