Clear screen command

[Trooper]

I am currently typing in a basic listing from a magazine and in the comments it says "In line 600 the curly bracket is a clear screen command".....now I can't find a way to enter such a command, could anyone help me out?

[Urchlay]

Press Escape, then shift and the Clear key (the shifted version of the less-than symbol). It'll print kind of an inverse video bent arrow that points up and to the left. If you don't press Escape first, it'll clear the screen when you type it.

 

You could also print CHR$(125) in a BASIC program.

[Trooper]

Thanks a lot!!

[Rybags]

Should be ? "<esc><clr>"; actually (semi-colon).

 

A handy trick: normally BASIC doesn't let you do GET/PUT etc to device 0 (which "E:" normally uses).

To get around that, use #16.

 

So, a printer-friendly CLS command would be

 

PUT #16,125

[atarixle]

you mean #6

(ATARI has only 8 Channels #0 ... #7)

[Rybags]

No, #16

 

BASIC disallows "0" on the GET/PUT statements. Not sure why, since it allows INPUT #0 and PRINT #0.

But, it performs an AND on the parameter you supply, so 16 gets converted to 0 and it lets it through.

 

#6 isn't always open. Try ?#6 on a fresh BASIC screen, you get an error. But, type GR.0 then ?#6 and the device will work.

[+Larry]

Should be ? "<esc><clr>"; actually (semi-colon).

 

A handy trick: normally BASIC doesn't let you do GET/PUT etc to device 0 (which "E:" normally uses).

To get around that, use #16.

 

So, a printer-friendly CLS command would be

 

PUT #16,125

 

Neat little trick!

 

There is another little trick that was once in INSIGHT: Atari that is related.

To get rid of the "?" prompt that results from an INPUT, use INPUT #16, XYZ.

 

Evidently works the same way, and although I've remembered and used this many times, I never understood its roots.

 

-Larry

[Rybags]

Forgot to mention that one. Discovered it some time ago too.

 

Likely that BASIC just outputs the ? if the device # is zero. You'd not want it to happen, for example if you had a concurrent I/O file open to disk, so they would have put that simple check in place.

Edited April 19, 2008 by Rybags

[atarixle]

Wow, not bad, that trick ...

 

The ATARI has 8 Channels, so it cuts the first unnessesary bit (16 - 2^4 = 0) ... but BASIC hides the '?' ...

I'm writing BASIC-programs for 16 years now ... but that trick is new for me :-)

 

thanks!

[Urchlay]

One minor gotcha regarding I/O with channel #16: if you plan to compile your program with the Turbo BASIC XL compiler, don't use this trick. It'll work in interpreted Turbo BASIC, and the compiler won't complain about it... but the runtime will stop the compiled program with an error message (in German, can't remember what it says) when it gets to the INPUT #16.

[+Larry]

One minor gotcha regarding I/O with channel #16: if you plan to compile your program with the Turbo BASIC XL compiler, don't use this trick. It'll work in interpreted Turbo BASIC, and the compiler won't complain about it... but the runtime will stop the compiled program with an error message (in German, can't remember what it says) when it gets to the INPUT #16.

 

Yes, and ditto ABC, although I can't remember whether it gives an error message or not.

 

We are so fortunate to have such a nice selection of languages for our 8-bits!

 

-Larry

[Rybags]

A possible workaround might be to use GET #A,B

 

Have variable A set to 0 for compiles, 16 for interpreter versions. No idea if that'll work though.