How to programmatically set the content type while creating a list item

If you create a new list item using the API without setting the content type id you will create a new item using the default content type.  However if you want to create a new list item using a different content type you will need to set the Content Type ID field.
The example below creates a list item using a content type called "Log" in a list called "HistoryLog".

using (SPSite site = new SPSite("http://intranet/"))
{
  using (SPWeb rootWeb = site.OpenWeb())
  {
    SPList historyLog = rootWeb.GetListFromUrl("/lists/historylog/allitems.aspx");
    SPListItem item = historyLog.Items.Add();
    item["LogType"] = "Warning";
    item["LogMessage"] = "Message .....";

    // set the content type id
    item["Content Type ID"] = rootWeb.ContentTypes["Log"].Id;
    
    item.Update();
  }
}