sub print_user {
      my $user_hashref = shift;
      print "user name = $user_hashref->{'name'}\n";
      print "user age  = $user_hashref->{'age'}\n";
   }

   ### main part of code ###
   my %user = { "name" => "John Doe",
                "age"  => 12 }
   print_user(\%user);