Maximum line length in basic exceeded by Compute! listing

[+KayBee]

Hi Atarians,

 

I am learning Atari basic and am entering in programs from COMPUTE!, Analog, etc. I am using a 48k Atari 400. I am experiencing an error that I think is due to the COMPUTE! program listing exceeding the maximum allowable characters per line.

 

The listing in the magazine shows this for line 503 I spaced it the same as the magazine listing :

503 IF A=54 THEN GRAPHICS 7:SETCOLOR 1,C

,12:SETCOLOR 2,C,6:SETCOLOR 0,C,4:SETCOL

OR 4,HUE,SHADE:POKE 764,255:? CHR$(253):

GOSUB 3000

And I get an error when typing in line 503. The basic interpreter hilites the position where the round bracket would be after :CHR$

I checked and retyped a few times and then thought there may be a limit to the number of characters per line number. From what I have read the Atari has a three-line limit, and this goes over three lines.

This program has a line 504 with another IF statement, so it seems that this program must have run somehow? I'd appreciate some guidance here. I also attached a clipping from the compute Issue, Aug 81, issue 15. I checked the following issue for Errata but didn't find any.

Thank you, I appreciate the help.

KB

[Nukey Shay]

Atari Basic allows you to use abbreviations for keywords. You use a period in place of the rest of the keyword name following one to three of its characters (dependent upon where in the list the keyword originates. Unfortunately, REM is the first keyword (as such its abbreviation is simply a period). Of the line you posted, GRAPHICS (GR.) and SETCOLOR (SE.) would be the big gainers. Also, don't forget that you don't need spaces except when a variable name is followed by an alphanumeric character.

[Nukey Shay]

503IF A=54THEN GR.7:SE.1,C,12:SE.2,C,6:SE.0,C,4:SE.4,HUE,SHADE:POKE764,255:?CHR$(253):GOS.3000 = 94 characters out of the 120 allowed (or 114 allowed if you are using the default left margin of 2). The latter is altered by POKE82,0 to get rid of the left margin.

[Nukey Shay]

BTW you can hack the list in the Atari Basic rom so that all keywords use unique two letter abbreviations (after you exhaust the initial 26 letters) to generate some impossible line listings when you reload the program into an unhacked Basic The keyword list is simply the ATASCII values of the characters, with the last letter of each keyword having the high bit set in addition, followed by the jumptable location. Line listings shortened too much may generate a stack overflow when Basic attempts to parse it!

[+Larry]

The mags took a lot of flak for those long lines! In addition to Nukey Shay's excellent explanation, usually those long lines can be tamed by just POKE 82, 0. And as you learn, consider a more full-featured Basic such as Turbo Basic which allows multi-line IF statements. IF: ELSE: ENDIF The closest thing to Atari Basic is the superb Altirra Basic. I think it also allows the improved IF structure.

[Rybags]

Yep. 114 characters (3*38) is the default limit you can type, E: limit is 120. Basic itself actually can accept 256 characters and sets up the input buffer as such which allows longer lines if using e.g. the ENTER "filespec" command.

That limit also allows overflow such that the first half of page 6 can get overwritten.

 

Also, now famously such exploits are used in the 10-liner Basic game competition.

[+KayBee]

Thank you Gentlemen, I appreciate you taking the time to answer. At it's best, this AtariAge forum is like a college class. Thanks again.

 

KB