Thanks again for your answer. I deleted my own post about half an hour later, I think, because I could solve my problems and moreover saw some stupid mistakes (as wrong variables' names) in my typing and didn't want to bother anyone with them. I thought deleting it would be better, I am sorry about this.
Well, to let you know how I solved it, here my scripts:
"recerca.php":
...
$qid=stripslashes($row['questionnaireid']);
$qyear=stripslashes($row['questionnaireyear']);
$qnum=stripslashes($row['questionnumber']);
echo '<td>Display information on<a href="scripts/pintador.php?qid='.$qid.'&qyear='.$qyear.'&qnum='.$qnum.'&showquestcount='.$showquestcount.'" target="Questionnaires"> questionnaires</a></td>';
...
"pintador.php":
...
$showquestcount=$_GET['showquestcount'];
$qid=$_GET['qid'];
$qyear=$_GET['qyear'];
$qnum=$_GET['qnum'];
$array_qid=explode("--",$qid);
$array_qyear=explode("--",$qyear);
$array_qnum=explode("--",$qnum);
...
Well, actually I have passed 19 variables through the url, some of them very long text strings concatenated with the separator "--". But the pieces of the scripts shown contain all what I have done.
Many thanks for your new answer. I will try to make it with "¿¿¿".