function Controlla() {
missinginfo = "";
if (document.cerca.datapart.value == "") {
missinginfo += "\n     -  Check-in";
}
if(document.cerca.datarit.value == "") {
missinginfo += "\n     -  Check-out";
}

if (missinginfo != "") {
missinginfo ="Füllen Sie:\n" +
missinginfo + "\n_______________________________";
alert(missinginfo);
return false;
}
else return true;
}