SaurabhKV

ADD SPFieldType.Choice, SPFieldChoice with SPChoiceFormatType.RadioButtons

using Microsoft.SharePoint;

using System.Collections.Specialized;

public void OnActivated(SPFeatureReceiverProperties properties)

{

    SPWeb web = (SPWeb)properties.Feature.Parent;

    string url = new Uri(web.Url).AbsolutePath;

    SPDocumentLibrary docLib = (SPDocumentLibrary)web.GetListFromUrl("Shared Documents/Forms/AllItems.aspx");

    // Create collection with choices.

    StringCollection categories = new StringCollection();

    categories.AddRange(new string [] {"Choice A", "Choice B", "Choice C"} );

    // Create new field in the project documents list.

    docLib.Fields.Add("MyNewField", SPFieldType.Choice, true, false, categories);

    // Set additional settings of the new field.

    SPFieldChoice fieldChoice = (SPFieldChoice)docLib.Fields["MyNewField"];

    fieldChoice.DefaultValue = "Choice A";

    fieldChoice.EditFormat = SPChoiceFormatType.RadioButtons;

    // Save settings.

    fieldChoice.Update();

    docLib.Update();

}