Undo checkout with PowerShell

I'm trying to undo a checkout with PowerShell but the function name doesn't seem to be recognized. Here is the code that I used.

$dList = [Microsoft.Sharepoint.SPDocumentLibrary]$list
            $items = $dList.Items
            $files = $dList.CheckedOutFiles
            foreach($file in $files)
            {

                $wuse = $file.DirName.Substring($web.ServerRelativeUrl.Length)
                Write ($web.Url+ "`t" + $wuse+"`/" + $file.LeafName +  "`t" + $file.CheckedOutBy.Name + "`t" + $file.TimeLastModified.ToString()+"`t" + "No Checked In Version" )

                $file.UndoCheckOut;


            }
            foreach($item in $items)
            {
                if ($item["Checked Out To"] -ne $null)
                {
                    $splitStrings = $item["Checked Out To"].ToString().Split('#')

                    Write ($web.Url+ "`t" + $item.Url + "`t" + $splitStrings[1].ToString() + "`t" + $item["Modified"].ToString() +"`t" + $item["Version"].ToString())

                    $item.UndoCheckOut;
                }
            }

Here is how I enable the powershell snap-in

Add-PSSnapin "Microsoft.SharePoint.PowerShell"