SPFieldChoice to the dropdown list programatically:

1. List Name: MyList
2. Choice Field Name: MyChoiceField and the values are
1. MyChoice1
2. MyChoice2
3.  MyChoice3

First example to set the SPChoice field default value as dropdown list default value.

          try
            {
                using (SPSite site = new SPSite(SPContext.Current.Site.ID))
                {
                    SPWeb web = site.OpenWeb(SPContext.Current.Web.ID);
                    SPList liMyLists = web.Lists["MyList"];
                    SPFieldChoice fcTypes = (SPFieldChoice)       
                                                liMyLists.Fields["MyChoiceField"];
                    ddlChoiceField.DataSource = fcTypes.Choices;
                   //To set choice field default value as dropdown list default value.
                    ddlChoiceField.SelectedValue = fcTypes.DefaultValue; 
                    ddlChoiceField.DataBind();
            }
            catch (Exception ex)
            {
               //code
             }

OutPut: