trouble with a segmented variable

[abaudrand]

Hi,

I'm trying to spare variables and started to rewrite my program by using a{0}, a{1}, etc... as most of them are TRUE/FALSE tag.

It worked fine when all variables were a,b,f,i etc... but now, I've just changed them, the compilation go wrong...

I've spent the last two night to scratch my head but can't see whats wrong...

 

[+Random Terrain]

I have to go out for a few hours. If nobody looks at it by then, I'll see if I can track down the problem when I get back.

[SeaGtGruff]

You can't check the value of a bit variable this way:

  if a{3} = 1 then missile1y=missile1y+1

Instead, you have to do it this way:

  if a{3} then missile1y=missile1y+1

That's to see if the bit is 1, or turned on (a "true" value). To see if the bit is 0, or turned off (a "false" value), use the ! or "not" operator, like this:

  rem * old line
  rem if a{1}=1 && a{2}=0 then missile0x=missile0x+d:missile0y=missile0y+e:goto DoneFire

  rem * corrected line
  if a{1} && !a{2} then missile0x=missile0x+d:missile0y=missile0y+e:goto DoneFire

Michael

[+Gemintronic]

SeaGtGruff to the rescue! My eyeballs were hurting looking for the syntax error. I didn't even know about that caveat with binary values. I take it

if a{1} = %1 then gosub way_sandwhich

wont work?

Edited July 22, 2010 by theloon

[SeaGtGruff]

SeaGtGruff to the rescue! My eyeballs were hurting looking for the syntax error. I didn't even know about that caveat with binary values. I take it

if a{1} = %1 then gosub way_sandwhich

wont work?

Correct; it would have to be

  if a{1} then gosub way_sandwhich

Michael

[abaudrand]

Thanks for the lesson of basic, guys!

I will rewrite my program later with that in mind!

[+Random Terrain]

SeaGtGruff to the rescue! My eyeballs were hurting looking for the syntax error. I didn't even know about that caveat with binary values. I take it

if a{1} = %1 then gosub way_sandwhich

wont work?

Yeah, the bB page says:

 

http://www.randomterrain.com/atari-2600-memories-batari-basic-commands.html#bit

Notice that bit operations do not use an equal sign in if-then statements.

 

Maybe it also needs a Warning message or a Did You Know? message.

[+Random Terrain]

I went with a Did You Know? box:

 

http://www.randomterrain.com/atari-2600-memories-batari-basic-commands.html#bit

 

See if that's OK.

[abaudrand]

thanks Random Terrain for "the did you know?". It's more clear for newbies like me