Print with comma

[XavSnap]

10 PRINT AT 0,0;"HOW ARE YOU TODAY?"
30 PRINT AT 0,1;"%O",

This bug seem to erase the last Y,X+1 character, and set X to 0 or 16.


@bwinkel67:
30 PRINT AT 0,1;"%O",, = 30 PRINT AT 0,1;"%O";"<space>";TAB 16;"<space>";TAB 0;


The 'PRINT ,' really display a space after the last Y,X pointer cursor.

10 FOR A=1 TO 44
20 PRINT "% % % % % % % % % % % % % % % % ";
30 NEXT A
35 PRINT AT 0,0;
40 FOR A=1 TO 20
50 PRINT TAB 4,,
60 NEXT A

Cap0033.jpg (6.59 KiB) Viewed 6371 times

[XavSnap]

May be a "RST 10H" with a AF register set to 0, before the cursor location refresh !

[bwinkel67]

More weird behavior on ZX81 BASIC.

This on the QL works as advertised resulting in either 1 when true or 0 when false (and is how it would work in most programming languages like C/C++). However, on ZX81 we get this:

PRINT 2 AND 17 -> results in 2
PRINT 17 AND 2 -> results in 17
PRINT 0 AND 17 -> results in 0
PRINT 17 AND 0 -> results in 0
PRINT 0 AND 0 -> results in 0

So if it's false it prints 0 but if it's true it takes the first argument.


With OR, the ZX81 is even less consistent (works as it should on the QL):

PRINT 2 OR 17 -> results in 1
PRINT 17 OR 2 -> results in 1
PRINT 0 OR 17 -> results in 1
PRINT 17 OR 0 -> results in 17
PRINT 0 OR 0 -> results in 0

So, OR results in 1 for all cases of true unless the second argument is false, then instead of 1 it results in the first argument???

Mind numbingly insane.

[1024MAK]

The ZX81 and ZX Spectrum BASIC treats any non-zero number as TRUE.

Hence the operation of AND and OR fits within this, returning zero if the expression result is false, and a non-zero value if the result is true.

The “strange” results often cause confusion. See the relevant section of the ZX81 BASIC manual exercise 3 and the ZX Spectrum BASIC manual.

I would have preferred binary bitwise operators myself

Mark

[1024MAK]

Mark

[1024MAK]

The above ties in with how IF works...

Mark

[XavSnap]

I would have preferred binary bitwise operators myself

Not False… But it's also True for me.

[bwinkel67]

The ZX81 and ZX Spectrum BASIC treats any non-zero number as TRUE.

Hence the operation of AND and OR fits within this, returning zero if the expression result is false, and a non-zero value if the result is true.

The “strange” results often cause confusion. See the relevant section of the ZX81 BASIC manual exercise 3 and the ZX Spectrum BASIC manual.

I would have preferred binary bitwise operators myself

Mark

I don't mind that it has 0 as false and non-zero as true. But the unique and weird thing is the evaluation result of an AND and OR. Most languages and the QL will give a 1 for the result of and AND or OR but activate as true for any non-zero in an IF. For the ZX81 to return the first argument as true in AND and convert to a 1 for OR is inconsistent. At least if there was consistency I would expect 2 OR 17 to return 2 and 17 OR 2 to return 17, not that I like that. I'd prefer those results to all be 1. Whereas I'm fine with IF 17 THEN PRINT "HELLO" to work. This will need fixing on the ZXSimulator as a work-around :-/

[Fruitcake]

I would have preferred binary bitwise operators myself

Which unlike the ZX81 and Spectrum is what the ZX80's AND and OR perform!

[mrtinb]

As the ZX81 uses a special calculator stack for most math operations, it is likely that the non zero integer was already on the stack, and to save time and space, it's easier just to return what is already there instead of replacing it with 1, to return 1.