my %rechenart = (
    '+' => sub { $_[0] + $_[1] },
    '-' => sub { $_[0] - $_[1] },
    '*' => sub { $_[0] * $_[1] },
    '/' => sub { $_[0] / $_[1] },
    '**' => sub { $_[0] ** $_[1] },
);

my @zeichen = qw# + - * / ** #;