Re: Recursion

[Larry Coon <larry@fs2.assist.uci.edu>]

Dirien B. Perez wrote:

> Hi I am having some problems with recursion I have the iterative
> version of a function that will calculate the sum of the elements is a
> linked list:
> 
>         function sum(list:cell_ptr) return integer is
>         local:cell_ptr:=list;
>         s:integer:=0;
>         begin
>                 while local /= null loop
>                 s:=s+local.value;
>                 local:=local.next
>                 end loop;
>         return s;
>         end sum;
> I need help creating the recursion version.

I don't want to do your homework for you (I'm assuming
that's what this is for), but it should be something like:

function sum (current_cell: cell_ptr) return int is
	if current_cell.next = null then
		return 1;
	else
		return sum (current_cell.next) + 1;
	end if;
end sum;

I'll leave it to you to modify this to correctly
distinguish an empty linked list from one with a single
item.  I'll also leave it to you to extrapolate from
this problem to your other problem.

Larry Coon
University of California
larry@fs2.assist.uci.edu
and lmcoon@home.com