Osea Algo asi
<? $cnt=mysql_connect("localhost","root","mysql");
mysql_select_db("data",$cnt);
$nfila=mysql_query("select id_tarea from tareas",$cnt);
while ($file=mysql_fetch_array($nfila))
{
$nultimo=$file['id_tarea'];
}
echo "Posicion ".strpos($nultimo,"-")."
";
if ($nultimo > 0) {
$x=$x+1;
} else {
$x=1 ;
}
$codigo=$x;
echo $codigo;
?>