@function = (
  sub {
    $_[0] + $_[1];
  },
  sub {
    $_[0] - $_[1];
  },
  sub {
    $_[0] * $_[1];
  },
  sub {
    $_[0] / $_[1];
  }
);
[...]
print $function[$f]->($zahl1, $zahl2);