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Forum Index : Microcontroller and PC projects : dim var as byte
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| matherp Guru  Joined: 11/12/2012 Location: United KingdomPosts: 10181 |
All MMBasic versions are identical in this respect. The quotes relate to the CONST command |
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Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1638 |
I think constants and variables are being confused CONST A = 123 'is an integer constant CONST B = 123.0 ' is a float constant C = 123 ' is a float variable unless OPTION DEFAULT INTEGER is used. Bill EDIT Peter types faster than I do. Edited 2022-08-04 07:17 by Turbo46 Keep safe. Live long and prosper. |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7820 |
You have to remember that the PicoMite isn't an 8-bit microprocessor. All the data paths on the RP2040 are 32 bits wide so attempting to use 8 or 16 bits is still going to use a minimum of 32 bits because of the hardware. A 64=bit integer is only 2 bus accesses. The highest bit is the sign, so you can handle some very big numbers. You can pack and unpack multiple bytes or 16-bit words into 64 bits if you want to, and write some little routines to handle it. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7820 |
I tried to read the application to CONST into it, but CONST is introduced later, on page 20, and there is apparently no relationship as the characteristic mentioned isn't shown in that section. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6266 |
There are two sections in the manual(s) The one describing CONST tells us that the CONT being declared will be an integer unless the value being assigned is a float, in which case the CONST will be a float. The section of the manual headed Constants I think refers to the type use within calculations. Type casting does occur but the starting position for a number is defined by whether it has a decimal or not etc. Type casting can do strange things. CONST a = CINT(123 /5) CONST b = 125 /5 CONST c = INT(123 /5) CONST d = 125.0 /5 PRINT a PRINT b PRINT d PRINT a/b PRINT c/b a is integer b is integer c is float d is ? Note the difference between CINT and INT I haven't tested the above in Microchip versions yet. Jim VK7JH MMedit |
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| Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1638 |
I believe that the two sections are talking about the same thing: Constants. The first section 'Constants' describes how a constant varies from a 'Variable' (which is described in the preceding paragraphs). The second section 'CONST' describes the use of the CONST command to define a constant. Bill Keep safe. Live long and prosper. |
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| lizby Guru Joined: 17/05/2016 Location: United StatesPosts: 3348 |
Lua is a dynamically typed language. For a=4, a is an integer. If followed by a=a/3, a becomes a floating point variable. MMBasic doesn't have dynamic typing. In the absence of setting the type of "a", for a=4, "a" is a floating point variable which happens to have a value which is an integer. dim integer i=4 a=4 if i=a then ?"Equal" ' prints "Equal" Or dim integer i=4 a=4 i=i/3 a=a/4 ?i,a ' prints 1 1.33333333 4 is a literal which has an integer value; 1.3 is a literal which has a floating point value. Assigning either literal to a variable doesn't change the variable type. The manual doesn't say anything that contradicts this. PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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| lizby Guru Joined: 17/05/2016 Location: United StatesPosts: 3348 |
Unless you are running out of variable space, it's neither weird nor wasteful to store integers as 64-bit numbers. I understand where you are coming from, since I came from the same place, and in particular it seemed painful for 1-bit flags to occupy 64 bits. CaptnBoing felt the same way, and in fruitoftheshed.com, he has routines for packing and unpacking multiple flags into a single word--but as he himself has said, what you gain in memory efficiency, you lose in running time. These days, it's almost always the case that the scarce resource is programmer time, not memory and not execution speed (there are exceptions, of course). MMBasic is great for enabling the minimization of programmer time in implementations which provide adequate speed and adequate memory for most of what hobby programmers need (and also for what some who program for a living need). PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2579 |
I have some time to waste so I will stick my oar in, for what little it may be worth. Part of the confusion about what the manual means may be due to the interpretation of "=" In normal arithmetic it means "is equal to" but not in Basic. In most programming languages, when use in a statement, it means "The value of variable to the left of = is replaced by an evaluation of all that is to the right" In other situations it is for comparing expressions etc. In A = 4 If A's type has not been fixed previously the integer constant 4 will be evaluated as a float when it replaces the current value of A in most Basics that I have used. Edited 2022-08-04 09:14 by phil99 |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6266 |
Ignore my earlier ramblings. OPTION DEFAULT FLOAT CONST a = &hFFFFFFFFFFFFFFFF CONST aa = -1.0 PRINT a b = a c% = a PRINT b PRINT c% PRINT "a" FOR n = 0 TO 7 PRINT HEX$(PEEK(VAR a,n),2); NEXT n PRINT "aa" FOR n = 0 TO 7 PRINT HEX$(PEEK(VAR aa,n),2); NEXT n PRINT "b" FOR n = 0 TO 7 PRINT HEX$(PEEK(VAR b,n),2); NEXT n PRINT "c" FOR n = 0 TO 7 PRINT HEX$(PEEK(VAR c%,n),2); NEXT n RUN -1 -1 -1 a FFFFFFFFFFFFFFFF aa 000000000000F0BF b 000000000000F0BF c FFFFFFFFFFFFFFFF > Note that the bytes are in reverse order. It still shows that CONST types depend on what you assign to them and do NOT follow the OPTION DEFAULT declaration. Jim Edited 2022-08-04 10:41 by TassyJim VK7JH MMedit |
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| lizby Guru Joined: 17/05/2016 Location: United StatesPosts: 3348 |
That should have been "a=a/3" instead of "a=a/4". PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 4032 |
I would rephrase that as: In A = 4 If A's type has not been fixed previously (and there's no OPTION DEFAULT INTEGER) then it (i.e. the variable A) will be float. The integer constant 4 will be stored in A. (This won't alter A being a float.) --- If you PRINT A it may confuse you! Don't be confused - the above is still true. --- CONST doesn't alter the above. A would still be a float if you assigned it using a CONST item (literal, in Tom's post). --- Also, because 4 can be represented (in the internal way used by the CPU) exactly as a float it will compare as equal in things like: IF A = 4 THEN ... That's because storing 4 into a float doesn't need any rounding etc. It fits fine but doesn't alter A being a float (once a variable has a type it keeps it). John Edited 2022-08-04 17:11 by JohnS |
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| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2579 |
" (and there's no OPTION DEFAULT INTEGER) " I would regard that as "has been fixed previously" since all variables are integers unless you specify otherwise in that case. Your other point is right, when "=" is used for a comparison an integer can be the same as a float. It's the value that is being compared not the type. While I am here I would like to expand another line from:- "The value of variable to the left of = is replaced by an evaluation of all that is to the right" to:- "The value of the variable to the left of = is replaced by an evaluation of all that is to the right, according to the rules of the language" Edited 2022-08-04 17:33 by phil99 |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7820 |
IMHO that's the best description so far, John. :) Perhaps all that's required to remove confusion is to add an additional sentence to the first manual reference: The later reference to CONST can then be left as it is. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1638 |
Sorry to labour the point but: A = 4 does not define a constant. you can follow that with: A = A + 1 BUT CONST A = 4 Does defines a constant it cannot be changed in this case A is an integer. CONST B = 5.0 is a float. Please RTFM. Bill Keep safe. Live long and prosper. |
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| Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1638 |
Bill Keep safe. Live long and prosper. |
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| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2579 |
My power to explain things clearly is inadequate. in A = 4 I should have said it is the number 4 that is the constant, it is not a variable so cannot be anything else. A is the variable and it's type is determined by the rules of the language, unless previously set. |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7820 |
For a CONST command the "=" sign is an assignment operator that assigns both the value *and type* of the expression to the "carrier". It ignores any previous assignment such as OPTION DEFAULT. The "carrier" isn't a variable - it just happens to look like one. :) The "carrier" then carries it's value and type so that it can be used elsewhere. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4299 |
Thanks folks, Regarding the type of CONST "variables", that is an interesting quirk of which I was unaware, though not relevant to me since I am a religious user of type suffixes on identifiers. Regarding the documentation, aren't we lucky to have such great documentation that we can pick nits with  .Have a great day, Tom MMBasic for Linux, Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7820 |
TBH I feel a bit rotten about the nit-picking as the manual is excellent. :( In this particular case I found it confusing though. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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