Add Properties or Delete List Folder Content Type

        private void button1_Click(object sender, EventArgs e)
        {
            string webURL = "http://richsharepoint:90/ApplicationManagement";
            SPSecurity.RunWithElevatedPrivileges(delegate()
            {
                using (SPSite site =new SPSite (webURL))
                {
                    using (SPWeb web = site.OpenWeb("ApplicationManagement"))
                    {
                        SPListCollection lists=web.Lists;
                        SPList list = null;
                        for (int i = 0; i < lists.Count; i++)
                        {
                            list = lists[i];
                            if (IsNeedList(list.Title))
                            {
                                ExtendFolderPerproty(web, list);
                            }
                        }
                    }
                }
            });
        }

        private bool IsNeedList(string listName)
        {
            string[] listNames = new string[] { "PictureLibraryAnson"};
            for (int i = 0; i < listNames.Length; i++)
            {
                if (listNames[i].ToString()==listName)
                {
                    return true;
                }
            }
            return false;
        }

        private void ExtendFolderPerproty(SPWeb web, SPList list)
        {
            SPContentType ct = list.ContentTypes["Folder"];
            ct.Sealed = false;
            //remove the properties
            ct.FieldLinks.Delete("NumberColumn");
            ct.FieldLinks.Delete("Direct_x0020_Link");
            ct.FieldLinks.Delete("Media_x0020_Category");
            ct.FieldLinks.Delete("Market_x0020_Category");
            ct.Update();
           //web.Fields.Add("NumberColumn", SPFieldType.Number,false);
            //SPFieldLink fLink1 = new SPFieldLink(web.Fields["NumberColumn"]);
            //ct.FieldLinks.Add(fLink1);

            //add Direct Link column
            string hColumnName = "Direct Link";
            web.Fields.Add(hColumnName, SPFieldType.URL, false);
            SPFieldLink hLink = new SPFieldLink(web.Fields[hColumnName]);
            ct.FieldLinks.Add(hLink);

            //add Media Category column
            MediaChoiceColumn(web, ct);
           ct.Update();
        }

        private void MediaChoiceColumn(SPWeb web, SPContentType ct)
        {
            string columnName = "Media Category";
            web.Fields.Add(columnName, SPFieldType.Choice, false);
            SPFieldChoice choicefield = (SPFieldChoice)web.Fields[columnName];
            // Add a group to the filed       
           // choicefield.Group = "MyGroup";
            // Add choices    
            string[] choiceItems = new string[] { "Bulletin","Junior Poster","Poster","Spectacular",
                "Wall","Wrapped Building/Poster","Mobile Billboard","Airport Media",
                "Bus Media","Rail/ Subway Media","Taxi Media","Mall Media",
                "Sports Media (Arena/Stadium)","Street Furniture","Place-Based Media (not Digital)",
                "Alternative/Promotional Media","Guerilla Media","Street Teams","Experiential / Event",
                "Digital Billboard","Digital Spectacular","Digital Poster","Digital Street Furniture",
                "Digital Airport Media","Digital Transit Media","Digital Mobile Media",
                "Digital Taxi Media","Digital Projection Media","Digital Place Based - Medical & Fitness",
                "Digital Place Based - Education & Office","Digital Place Based - Leisure",
                "Digital Place Based - Retail", "Digital Alternative Media","Mobile Media"
            };
            for (int j = 0; j < choiceItems.Length; j++)
            {
                //add choice
                choicefield.Choices.Add(choiceItems[j].ToString());
            }
            choicefield.EditFormat = SPChoiceFormatType.Dropdown;
            // Set the default choice        
            choicefield.DefaultValue = "Bulletin";
            choicefield.Update();
            SPFieldLink fl= new SPFieldLink(choicefield);
            ct.FieldLinks.Add(fl); 

        }

       //Delete list folder content type
       private void button2_Click(object sender, EventArgs e)
        {
            string webURL = "http://shengvm77:84" ;
            try
            {
                SPSecurity.RunWithElevatedPrivileges(delegate()
                {
                    using (SPSite site = new SPSite(webURL))
                    {
                        using (SPWeb web = site.OpenWeb("HomeAnson"))
                        {
                            SPListCollection lists = web.Lists;
                            SPList list = null;
                            for (int i = 0; i < lists.Count; i++)
                            {
                                list = lists[i];
                                if (list.Title == "PicAnson")
                                {
                                    SPContentType ct = list.ContentTypes["Folder"];
                                    list.ContentTypes.Delete(ct.Id);
                                    list.Update();
                                    break;
                                }
                            }
                        }
                    }
                });
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            
        }