function checkWrite()
{
var a='';
textstring = 'Silo ';
for (i=0; i<5; i++) {
box = document.forms[0].elements[i];
a=trim(box.value);
if (!a='') {
alert('Compilare il campo ' + box.name + '!');
box.focus()
return;
}
textstring += box.name + ' ' + box.value + ', ';
}

select_box1 = document.modulo.anno.options[document.modulo.anno.selectedIndex].value
select_box2 = document.modulo.fornito.options[document.modulo.fornito.selectedIndex].value
textstring += 'completo di:\n';
document.forms[0].output.value = textstring;
}