Label as a string var - Printable Version

Label as a string var - Printable Version

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Label as a string var - oblo - 11-06-2012

Hi all

Long time no see around here :oops: but now I'm getting some free time to spend with ZX Basic, so I hope to come more often Smile

In fact, I have a question: I want to store a label name in a variable, in order to do GOSUBs using a var, not fixed names. I made this code so far, but it fails with the message 'identifier 'eti$' is a var, not a label':

Code:
#INCLUDE <keys.bas>

paper 0: border 0: ink 7: cls

dim eti$

eti$="l01"

while 1=1

    if Multikeys(KEY1)<>0 then

        eti$="l01"

        gosub eti$

    elseif Multikeys(KEY2)<>0 then

        eti$="l02"

        gosub eti$

    elseif Multikeys(KEY3)<>0 then

        eti$="l03"

        gosub eti$

    end If

end While

l01:

print at 0,0;ink 1;"ESTAS EN LA ETI1";

RETURN

l02:

print at 0,0;ink 2;"ESTAS EN LA ETI2";

RETURN

l03:

print at 0,0;ink 3;"ESTAS EN LA ETI3";

RETURN

Can be it done or what I'm asking is impossible right now? Note that I'm asking for a string, not numbers.

Thanks and regards

Re: Label as a string var - britlion - 11-11-2012

oblo Wrote:Hi all

Long time no see around here :oops: but now I'm getting some free time to spend with ZX Basic, so I hope to come more often
In fact, I have a question: I want to store a label name in a variable, in order to do GOSUBs using a var, not fixed names. I made this code so far, but it fails with the message 'identifier 'eti$' is a var, not a label':

Code:
#INCLUDE <keys.bas> paper 0: border 0: ink 7: cls dim eti$ eti$="l01" while 1=1 if Multikeys(KEY1)<>0 then eti$="l01" gosub eti$ elseif Multikeys(KEY2)<>0 then eti$="l02" gosub eti$ elseif Multikeys(KEY3)<>0 then eti$="l03" gosub eti$ end If end While l01: print at 0,0;ink 1;"ESTAS EN LA ETI1"; RETURN l02: print at 0,0;ink 2;"ESTAS EN LA ETI2"; RETURN l03: print at 0,0;ink 3;"ESTAS EN LA ETI3"; RETURN

Can be it done or what I'm asking is impossible right now? Note that I'm asking for a string, not numbers.

Thanks and regards

It can't be done that way, since labels are static - they are memory addresses, effectively. So at run time, there's no such thing as "eti#" - a call to eti1 is replaced by a jp nnnn instruction, so far as I can tell.

You'd have to make a jump table, or an array of address, and use that if you wanted to be able to leap to specific ones. That or have a routine that has an if else else else else to gosub based on a variable. Compiled code really doesn't allow calculated gotos in this way.

Also, it's good programming practice to avoid goto and gosub where possible. I wrote a pac man game too (can I still your awesome pac man beeps intro some time for it? Smile

) And published the source code and a tutorial - have a look in the wiki ( <a class="postlink" href="http://www.boriel.com/wiki/en/index.php/ZX_BASIC:Tutorials">http://www.boriel.com/wiki/en/index.php ... :Tutorials</a> )

Re: Label as a string var - oblo - 11-12-2012

Thanks. Now I realize that it's impossible, I have to redone the engine from scratch, but it seems its better than I was doing.
About the Pac-Man intro, what do you mean with 'can I still your awesome pac man beeps intro some time for it?'? If you're asking permission for re-use it, please do it Big Grin

The source code I released is for that (well, and see how a bad programmer I am) :mrgreen:

Cheers

Re: Label as a string var - britlion - 11-13-2012

I'm playing with <a class="postlink" href="http://www.worldofspectrum.org/infoseekid.cgi?id=0027713">http://www.worldofspectrum.org/infoseek ... id=0027713</a> to see about updating it.

I wrote a tutorial for ZX Basic on how I did that - and you may find some hints and tips useful. OCMan is very cool - but hard to read. You still have line numbers. (And my ability to read in Spanish is not good, which doesn't help Wink

I try to write procedurally - so I have things like

updateGhosts()
displayScore()
MovePlayer()

As procedures - it should (language aside) hopefully be clear what each line does at the top level.

In fact - my main loop and start point is crazy simple to read (and does so much!) - Without comments and fluff - the whole running game looks like this as a loop:

Code:
'Main loop

    do

        updatePlayer()

        updateGhosts()

        collisionCheck()

        updateTimers()

    loop

So I'm suggesting that you can use this procedural bottom up/ top down approach to make programs easier to read - and being more modular, you can more easily re-use parts in other programs.

For example print42 is just a few subroutines, really - but it's easy to plug into another program from the library!