use strict;
use warnings;
use CGI;
#use CGI::Carp qw(fatalsToBrowser);

my $cgi       = CGI->new;
my @Feldnamen = $cgi->param();

my $ergebnis;

my $wert1 = $cgi->param('wert1') // '';
$wert1 = '?' if not length $wert1;

my $wert2 = $cgi->param('wert2') // '';
$wert2 = '?' if not length $wert2;

if ( $wert1 ne '?' and $wert2 ne '?' ) {
    $ergebnis = $wert1 + $wert2;
}
else {
    $ergebnis = 'ERROR: Werte fehlen';
}

print $cgi->header(),
  $cgi->start_html('CGI-Feedback'),
  $cgi->h1('Taschenrechner '),
  $cgi->i('Dein Ergebnis:');
foreach my $Feld (@Feldnamen) {
    print $cgi->param($Feld), $cgi->br;
}
print $cgi->strong($ergebnis), $cgi->br;

print $cgi->end_html();