Sinclair ZX80 / ZX81 / Z88 Forums

Last night I had an issue with ZX BASIC in that I was getting an odd result when LET M=.25 and I took .25 away. The result was not zero. I don't remember exactly but the number returned was something like 1.141322E-10

I fixed it like this:
This might be how I had EightyOne set up. In what other circumstances could this happen?

Thanks,

Shaun.

If you calculating with floating point values these may loose precision over the time (during calculations).
You could use INT to round them. Be aware that INT only cuts the value, doesn't round up.

For two digits you could use something like this: This should round correctly:

So where I'm looping and decreasing a value (each loop is LET M=M-.25), I'm fixing with this:
This should therefore basically call the INT function every 4th loop and will hopefully will fix recursive rounding errors.

Regards,

Shaun.

This problem exists on the ZX Spectrum BASIC as well.

The way that real numbers are handled internally is not always exactly the same. As these are floating point numbers, using the = or <> operators, you often get unwanted results.

In my programs I test for a small range of values using the greater than and less than operators.

Mark

"ZxBasic"..."editor"... from XavSnap? http://dskcenter.free.fr/zxtools

Ooops!

Yes, in "ZxBasic editor","ZxToken" and "Vb81 XuR" text input (loaded in the file explorer), the Visual basic give a corrupt value for numbers lower than ".5".
It's a Vb integer fault, due to an internal error!

If a text file is imported to "ZxBasic editor","ZxToken" or "Vb81 Xur" (same import codes used), just convert the number to a VAL"xxxx" function!
For all of values lower than .5 !


Example:
10 LET M=.2 >>> 10 LET M=VAL".2"

10 LET M=.123456789 >>> 10 LET M=VAL".123456789"

NOTE:
To save a file in a "ZxBasic editor" format, just type : SAVE"MYPROG.TXT"
The text file will be saved in text format (ASM hex/dec+BASIC) in the current work directory.

You could also just use integers and only display the amount of "money" on screen as possible turns/4.
Then you can decrease the integer and the calculation error will not occur.

For the game it could be useful to think of coins only which are transferred into a sum in display routine only.
This way you can adapt the game more easily when inflate is getting higher or let the user choose it's own currency and set an appropriate amount.
A quarter dollar is quite different to a quarter rubel (RUB) when people from Russia like to play.
This would be a nice add-on to choose the country first (maybe just from a list).

And as for keeping the quarters on display on the ZX80:
LET M=INT (T/4)
LET Q=(T-M*4)*2+1
PRINT M;".";"00255075"(Q TO Q+1)

dr beep wrote: ↑Wed Mar 01, 2017 10:25 am And as for keeping the quarters on display on the ZX80:
LET M=INT (T/4)
LET Q=(T-M*4)*2+1
PRINT M;".";"00255075"(Q TO Q+1)

Does this work with the 4K ROM?

Thanks,

Shaun.

This works....