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Forum Index : Microcontroller and PC projects : mm2 Newbie Variable Questions
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| JackRabbit Newbie  Joined: 21/07/2018 Location: United StatesPosts: 14 |
Can I DIM a variable as an unsigned integer or should I just do: myvar = &H00 Is there any way to define a variable as a byte or 16 bit word variable? Is there any built-in functionality to parse variables into bytes? I wrote a checksum calculation for the SHT31 temp/hum sensor and it does a lot of << and >> to lose excess bytes from the values so I'm thinking there may be a better way. |
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panky Guru  Joined: 02/10/2012 Location: AustraliaPosts: 1114 |
JackRabbit, There are only 3 types of variable in MMBasic:- 1. Floating point; 2. 64 bit signed integer; and 3. Character (string). The MMBasic 2 User manual has a detailed explanation starting on page 34. It explains how you can treat signed integers as unsigned but with limitations and caveats. I don't believe there are any built in ways of doing either of your last two questions - others may have some ideas. panky ... almost all of the Maximites, the MicromMites, the MM Extremes, the ArmMites, the PicoMite and loving it! |
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| JackRabbit Newbie Joined: 21/07/2018 Location: United StatesPosts: 14 |
Thanks :) I have read that part of the manual, it says "64-bit unsigned numbers can be created using the &H, &O or &B prefixes to a number and these numbers can be stored in an integer variable." What wasn't clear to me was whether "created" included by means of a DIM. |
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Azure Guru Joined: 09/11/2017 Location: AustraliaPosts: 446 |
It is good programming practise to always define/declare your variables and not just use them and have them created automatically. You can use the OPTION EXPLICIT command in MM Basic to force this. That way any typos in a variable name do not become problems in your code. So you would then use the DIM or Local (for Subs and Functions) as appropriate to create your variables. |
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| JackRabbit Newbie Joined: 21/07/2018 Location: United StatesPosts: 14 |
Noted, Python and php have ruined me :( |
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| Azure Guru Joined: 09/11/2017 Location: AustraliaPosts: 446 |
You can leave out OPTION EXPLICIT and just have MM Basic create variables as you write them in your code (except for arrays they must be DIMensioned hence the name). Perfectly fine for small programs. Tends to be a trip up as the program gets larger, more complicated or modified over time. |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 4044 |
DIM would create a variable (of whatever type), whereas the part you quoted refers to numbers (via &H etc). The number is just that: a number. If you wish you can store it (i.e. hold it) in a variable. A variable has a type (or is in effect any type as the original BASIC did things). (There are also arrays.) If you just need part of the 64 bits then you can either ignore the other bits or (for example) mask them off (typically using AND). It's usually fairly easy to treat a variable as a byte (or as a 16-bit word) by ANDing with &Hff (or &Hffff). You might like to post a code fragment in case someone offers a shorter version. John |
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| Atomizer_Zero Senior Member  Joined: 04/07/2020 Location: United KingdomPosts: 134 |
I'm actually having an issue with this right now. DIM a = &H00 DIM b = &H00 DIM c = &H00 DIM d = &H00 d = ((a^b) AND (a^c) AND &H00) print d when I run this I get Domain error in pow [6] d = ((a^b) AND (a^c) AND &H00) Error: OverFlow As far as I'm aware, "d" should be 0, considering all variables are 0. I've tried various varieties of variable declarations. The only way this passes is if I DON'T declare the variables (literally, just "d = ((a^b) AND (a^c) AND &H00)", works). Any ideas? Edited 2020-07-17 10:07 by Atomizer_Zero |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
What version of MMBasic and what device? Jim VK7JH MMedit |
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| Atomizer_Zero Senior Member Joined: 04/07/2020 Location: United KingdomPosts: 134 |
Thats a good point, as of right now I'm still stuck with MMBasic for Win/DOS. Sorry, I should have mentioned that. |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
try declaring them as INTEGER VK7JH MMedit |
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| Atomizer_Zero Senior Member Joined: 04/07/2020 Location: United KingdomPosts: 134 |
THANK YOU. Seriously... I've been pulling my hair out for ages. I didn't even think to try it that way. For clarity, this works fine. DIM INTEGER a = &H0, b = &H0, c = &H0, d = &H0 d = ((a^b) AND (a^c) AND &H00) print d Thanks again! |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
any number to power zero = 1 zero to any power = 0 zero to the power zero will always cause much heated discussion. It should be classed as indeterminate but most software will treat it as one. It looks like the DOS version has a problem with 0^0 for floats but OK for INTEGERs Jim VK7JH MMedit |
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| Paul_L Guru Joined: 03/03/2016 Location: United StatesPosts: 769 |
Be careful with the use of a type in a declaration. DIM a=&H0, b=&Ho, c=&Ho, d=&Ho as integer might declare a, b, and c as floating point variables and d as an integer variable. DIM integer a=&H0, b=&Ho, c=&Ho, d=&Ho probably makes a, b, c, and d integer varaibles. DIM a%=&H0, b%=&Ho, c=&Ho, d%=&Ho will makes a, b, and d integer variables, but it might make c a floating point. The use of % or $ as a type specifier should be restricted to the declaraation statements. If you include either in assignment or comparison statements I believe that it will slow the execution of the code somewhat. DIM i%, a%, b% ' this might be slower ' it forces the interpreter to check the types on each iteration for i%=1 to 10000 a%=i%+b% next i% ' this might be faster for i=1 to 10000 a=i+b next Only Geoff knows for sure! Paul in NY |
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| zeitfest Guru Joined: 31/07/2019 Location: AustraliaPosts: 581 |
AFAIK (I think) integers on MM are always signed.. ie if the most significant bit is used it will result in a negative number. (?) ed - or something similar, I do not know the details with MM. Edited 2020-07-17 11:19 by zeitfest |
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| Paul_L Guru Joined: 03/03/2016 Location: United StatesPosts: 769 |
Leave it to someone from Tasmania to bring up 0^0!  If (a house)^0=1 and (a donkey)^0=1 does that mean that (a house)=(a donkey)????  And, bye the way, does TAN(90°) really equal positive infinity and TAN(270°) equal negative infinity???????  Paul in NY |
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| zeitfest Guru Joined: 31/07/2019 Location: AustraliaPosts: 581 |
or maybe the most negative number possible in MM is 63 bit ? Experts please clarify ? |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
MMBasic uses signed integers 64 bit signed integers are 63 bits plus sign bit That give you +-9.22x10^18 VK7JH MMedit |
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Womble Senior Member Joined: 09/07/2020 Location: United KingdomPosts: 267 |
very true Paul. This one has been biting me in the butt frequently when trying to port some of my old GW/QBasic code. Geoff has a very good point when he put this in the manual: When OPTION EXPLICIT is used (as recommended) the DIM, LOCAL or STATIC commands are the only way that a variable can be created. If this option is not used then using the DIM command is optional and if not used the variable will be created automatically when first referenced. This I did not know. Makes sense though. BTW. mixing DIM declarations, with Type Suffixes (!,%,$,etc.) and automatic variable creation constitutes a Really Bad Idea ... much swearing and head scratching will ensue. Even for small programs, pick one method and stick to it. Lots of comments might help, but you will end up confusing and frustraing yourself. There is a reason Wombles are grey  Edited 2020-07-17 21:53 by Womble |
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| zeitfest Guru Joined: 31/07/2019 Location: AustraliaPosts: 581 |
What happens when the most significant bit is set, in MM ? Is the whole value used as a positive number ? |
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