[Beginner Problem] Varibles not getting assigned correctly

[Beginner Problem] Varibles not getting assigned correctly

[Shane Smith]

Hi all,

I'm trying to write a simple program (that manacla game), I've 
encountered a problem where the variables that are used in a nested 
procedure can't be assigned a value. I'm using GNAT 4.1.2 on Linux.

---CODE---

procedure Manacla is

type pits is array (1 .. 14) of Integer;
type Score_Type is array (1 .. 2) of integer;
type arr_point is access pits;
board : arr_point;

Score1 : Integer := 0;
Score2 : Integer := 0;
Scores : Score_type := (0,0);
Player : Integer range 1 .. 2 := 1;
Winner : integer := 0;
Test : constant integer := 11;
Pit : Integer := 0;

...

procedure Status (Player : in integer)
is

begin
	-- Check if 'playing pits' are empty, if not exit
	while board.all(2 .. 7) = (0,0,0,0,0,0) or board.all(9 .. 14) = 
(0,0,0,0,0,0) loop

		if Player = 1 then
			if board.all(2 .. 7) = (0,0,0,0,0,0) then
				Winner := 1;
			else exit;
			end if;
		else
			if board.all(9 .. 14) = (0,0,0,0,0,0) then
				Winner := 2;
			else exit;
			end if;
		end if;
	end loop;
end Status;

...

procedure Player1
is
Pit : Integer := 0;
Player : Integer := 1;

begin
...
Status(Player);
end PLayer1;

begin
...
player1;
end Manacla;

---END CODE---

Basically main body calls player1 and player1 calls status(player) (which 
edits the winner variable).

In gdb 'p winner' gives "$14 = 7270388".
It happens to arrays and access varibles as well.

Re: [Beginner Problem] Varibles not getting assigned correctly

[Niklas Holsti]

Shane Smith wrote:
> Hi all,
> 
> I'm trying to write a simple program (that manacla game), I've 
> encountered a problem where the variables that are used in a nested 
> procedure can't be assigned a value. I'm using GNAT 4.1.2 on Linux.

I think your conclusion ("can't be assigned a value") is too 
strong; what you really observed is "gdb displays an unexpected value".

I occasionally get weird values from gdb (which I seldom use, 
though) from Ada programs, where a Text_IO.Put at the same place 
shows the correct, expected value.

> type arr_point is access pits;
> board : arr_point;

It's not necessarily relevant, but I'm curious why you use an 
access type for the board. Are there several boards? (I don't know 
this game.)

By the way, even with an access type, you don't need the ".all" 
below, where you write board.all(2 .. 7), you can write just 
board(2 .. 7). The ".all" is implied when you index an array or 
take a slice of it.

> procedure Status (Player : in integer)
> is
> 
> begin
> 	-- Check if 'playing pits' are empty, if not exit
> 	while board.all(2 .. 7) = (0,0,0,0,0,0) or board.all(9 .. 14) = 
> (0,0,0,0,0,0) loop

Why are you looping here? The only thing that may change in the 
loop is the Winner variable, so the loop either never starts, or 
exits in the first iteration, or never exits.

> 		if Player = 1 then
> 			if board.all(2 .. 7) = (0,0,0,0,0,0) then
> 				Winner := 1;

If this happens, the loop gets stuck and never exits.

> 			else exit;
> 			end if;
> 		else
> 			if board.all(9 .. 14) = (0,0,0,0,0,0) then
> 				Winner := 2;

Same here.

> 			else exit;
> 			end if;
> 		end if;
> 	end loop;
> end Status;
> 
> In gdb 'p winner' gives "$14 = 7270388".

At what point in the program did you give that gdb command? That 
is, where did you break the program's execution?

If I had this problem I would first use Text_IO, not gdb, to print 
out the values of the variables. If you do that, and you still get 
the wrong value, perhaps you could show a bit more of the program 
in your nest posting.

HTH

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .

Re: [Beginner Problem] Varibles not getting assigned correctly

[Peter Hermann]

Shane Smith <rusty_@users.sourceforge.net> wrote:
> I'm trying to write a simple program (that manacla game), I've 

you might have a look at
http://www.sofport.com:5055/appletmagic/download/
;-)

Re: [Beginner Problem] Varibles not getting assigned correctly

[Jeffrey R. Carter]

Shane Smith wrote:
> 
> type pits is array (1 .. 14) of Integer;
> type Score_Type is array (1 .. 2) of integer;

Your code would be easier to understand (and hence to comment on) if you were 
consistent in your capitalization.

What does it mean for a pit or a score to be negative? Perhaps Natural or 
another type or subtype based on the rules of the game would be better for the 
component types here.

I presume the index of Score_Type represents a specific player. Using numbers is 
probably not a good way to identify a player; an enumeration type might be better:

type Player_ID is (Human, Computer);

or some such.

> type arr_point is access pits;
> board : arr_point;

I see no reason to use access types in this program.

> procedure Status (Player : in integer)

It appears that the purpose of Status is to assign to Winner. It's usually 
clearer to pass parameters than to modify global variables. I would think you'd 
want something like

procedure Status
    (Player : in Player_ID; Board : in Pits; Winner : out Player_ID);

Others have addressed your questions, so I won't repeat that here. I haven't 
used a debugger for years, so I find it usually quicker to stick in some output 
that to relearn how to use one. Given that gdb sometimes misbehaves, it can be 
more effective, too.

-- 
Jeff Carter
"Propose to an Englishman any principle, or any instrument, however
admirable, and you will observe that the whole effort of the English
mind is directed to find a difficulty, a defect, or an impossibility
in it. If you speak to him of a machine for peeling a potato, he will
pronounce it impossible: if you peel a potato with it before his eyes,
he will declare it useless, because it will not slice a pineapple."
Charles Babbage
92

Re: [Beginner Problem] Varibles not getting assigned correctly

[Steve]

"Shane Smith" <rusty_@users.sourceforge.net> wrote in message 
news:13oe10uh39g0v85@corp.supernews.com...
> Hi all,
>
> I'm trying to write a simple program (that manacla game), I've
> encountered a problem where the variables that are used in a nested
> procedure can't be assigned a value. I'm using GNAT 4.1.2 on Linux.
>

Hi.
Since you volunteered "beginner" problem I would like to make a suggestion 
on program structure.
When I was in college (a couple of decades ago) where I learned Pascal, one 
of my instructors had the requirement that no global variables were 
permitted.  Only global types.

If you are want to avoid using multiple packages (until you're a little... 
very little) farther along you can structure the main procedure:

procedure Manacala is

  procedure A( ... args ... ) is
  begin
     ...
  end A;

  procedure Main is
    ... variables delclared here ..
  begin
    ... code here that passes arguments to other procedures/functions
  end Main;

begin
  Main;
end Manacala;

When programs are broken down this way you can understand the operation of a 
procedure or function based on just the arguments and the type definitions. 
This makes it easy to understand small pieces of code and how they interact 
with data.

Regards,
Steve
(The Duck)


> ---CODE---
>
> procedure Manacla is
>
> type pits is array (1 .. 14) of Integer;
> type Score_Type is array (1 .. 2) of integer;
> type arr_point is access pits;
> board : arr_point;
>
> Score1 : Integer := 0;
> Score2 : Integer := 0;
> Scores : Score_type := (0,0);
> Player : Integer range 1 .. 2 := 1;
> Winner : integer := 0;
> Test : constant integer := 11;
> Pit : Integer := 0;
>
> ...
>
> procedure Status (Player : in integer)
> is
>
> begin
> -- Check if 'playing pits' are empty, if not exit
> while board.all(2 .. 7) = (0,0,0,0,0,0) or board.all(9 .. 14) =
> (0,0,0,0,0,0) loop
>
> if Player = 1 then
> if board.all(2 .. 7) = (0,0,0,0,0,0) then
> Winner := 1;
> else exit;
> end if;
> else
> if board.all(9 .. 14) = (0,0,0,0,0,0) then
> Winner := 2;
> else exit;
> end if;
> end if;
> end loop;
> end Status;
>
> ...
>
> procedure Player1
> is
> Pit : Integer := 0;
> Player : Integer := 1;
>
> begin
> ...
> Status(Player);
> end PLayer1;
>
> begin
> ...
> player1;
> end Manacla;
>
> ---END CODE---
>
> Basically main body calls player1 and player1 calls status(player) (which
> edits the winner variable).
>
> In gdb 'p winner' gives "$14 = 7270388".
> It happens to arrays and access varibles as well.