functions & program flow for a noob

Archiver

Hello...

I am very used to program flow in
php/javascript/java/etc, but I am unsure how to
accomplish similar things in PBASIC.

What techniques are used to pass values to functions?
How are functions constructed in PBASIC? Say I have
an associative array (I know this is in improper
lingo) and want to sent a key and that array to a
function, receiving back the value contained within
the key.

Is there an equivalent in PBASIC? Am I thinking
backwards here? Pipe dreams? Gimme the scoop,
thanks!

--t

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Archiver

Hi

For something like associative arrays (well, rather a lookup table)
see the stamp manual for the commands LOOKUP and LOOKDOWN.

PBasic does not provide local variables or argument passing to
functions, it does not even provide functions to be exact. There are
several ways to pass arguments to subroutines: global variables, the
scratchpad RAM (BS2xx only) or the EEPROM storage (only approriate
for mostly constant parameters).
Don't forget you have only 26 byte of RAM.

subroutines (as a replacement for functions) in PBasic have the
folowing form:

'subroutine call
gosub label
...

'a subroutine
label:
'subroutine code
return

Regards
Adrian

Archiver

The following applies to PBasic 2.0.
PBasic 2.5, currently in Beta, has
better control flow (IF...THEN).

PBasic 2.0 'function' implementation:
1. PBasic only has GOTO and GOSUB.
(OK, BRANCH is computed GOTO)
2. PBasic has NO 'local' variables
(Variables local to a function, allocated on
the stack).
3. PBasic only allows you 4 nested levels of GOSUB.
4. PBasic has NO 'stack' that you can use.
5. PBasic 'IF..THEN' is only a conditional GOTO.
6. You have 26 BYTEs of Register space for variables.
-- These can be allocated in ANY combination of
-- BIT, NIB, BYTE, or WORD (ALL UNSIGNED)
-- 1, 4, 8, 16 bits each.

So:
Temp1 VAR BYTE
Temp2 VAR BYTE
Temp3 VAR BYTE

Parm1 VAR BYTE
Parm2 VAR BYTE
Result VAR BYTE

MAIN:
Temp1 = 5
Temp2 = 6
GOSUB MyFunc ' Uses 'Temp1' and 'Temp2' to make 'Temp3'
IF Temp3 = 0 THEN Skip1 ' implied: GOTO Skip1
' ELSE
Result = Temp3
Skip1:
GOTO MAIN
END

'***** Subroutines ****
MyFunc:
Temp3 = Temp1 + Temp2
RETURN

If you do this, be very careful if 'MyFunc' calls
another subroutine, don't assume it has its 'own'
Temp1, Temp2, and Temp3. These are GLOBALS.

--- In basicstamps@yahoogroups.com, "mr. t" <nadanada@e...> wrote:
> Hello...
>
> I am very used to program flow in
> php/javascript/java/etc, but I am unsure how to
> accomplish similar things in PBASIC.
>
> What techniques are used to pass values to functions?
> How are functions constructed in PBASIC? Say I have
> an associative array (I know this is in improper
> lingo) and want to sent a key and that array to a
> function, receiving back the value contained within
> the key.
>
> Is there an equivalent in PBASIC? Am I thinking
> backwards here? Pipe dreams? Gimme the scoop,
> thanks!
>
> --t
>
> __________________________________
> Do you Yahoo!?
> SBC Yahoo! DSL - Now only $29.95 per month!
> http://sbc.yahoo.com

Archiver

Good to know that about gosub, Allan, thanks! May have been the
cause of previous unsolved mysteries...
To add my 2 cents...
If something doesn't work, there are no exception throws, the
program dumps to the next command (memory address?).
Let the 'debug' statement be your dear friend for showing you what
is happening.
Negative (signed) numbers must be words. I'd steer clear of them
all together if you can...

You maybe thinking the Javelin stamp is more up your alley - You
have to use their 'special subset' of java - very limited. I had a
bad experience with them and trying to pass serial data... you need
the special Javelin carrier board to do serial comm (which isn't
sold outside the kit).

-Damon

--- In basicstamps@yahoogroups.com, "Allan Lane" <allan.lane@h...>
wrote:

> 3. PBasic only allows you 4 nested levels of GOSUB.