my $array_ref = [ qw( 1 4 9 10 15 23 34 84 100 ) ]; add_n_to_values_and_print( $array_ref, 15 ); sub add_n_to_values_and_print{ my ( $list, $add ) = @_; for my $value ( @$list ){ $value += $add; print $value; } } #### my $array_ref = [ qw( 1 4 9 10 15 23 34 84 100 ) ]; add_n_to_values_and_print( $array_ref, 15 ); sub add_n_to_values_and_print{ my ( $list, $add ) = @_; # dereference and work with a local copy of the array my @local_list = @$list; for my $value ( @local_list ){ $value += $add; print $value; } }