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Forum Index : Microcontroller and PC projects : MM Basic - passing by reference help

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Nimue

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Joined: 06/08/2020
Location: United Kingdom
Posts: 420
Posted: 01:29pm 22 Jan 2021
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I have written code to check for palindromic hex and binary numbers.  Except it doesnt work -- due to passing by reference and I can't find a way out of it:

Function reverse(in_string$) As string
   For i = Len(in_string$) To 1 Step -1
       b$=Mid$(in_string$,i,1)
       r$=r$+b$
   Next i
   reverse$=r$
End Function


For i = 1 To 100
   If Bin$(i) = reverse(Bin$(i)) Then
       If Hex$(i) = reverse(Hex$(i)) Then
           Print i,Bin$(i), Hex$(i)
       EndIf
   EndIf
Next i


The function works fine (outside of the for loop)  as does the hex / bin conversions.  The link between the loop and the function breaks and this leads me to think is a passing issue (by reference?)

Any minds greater than mind have a look at this for me please?

Nim
Edited 2021-01-22 23:30 by Nimue
Entropy is not what it used to be
 
thwill

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Joined: 16/09/2019
Location: United Kingdom
Posts: 4311
Posted: 01:36pm 22 Jan 2021
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Hi Nimue,

Unfortunately I'm not near my CMM2 so can't run it for myself.

I can't see an obvious pass-by-reference issue; reverse() doesn't do any "write operations" to in_string$.

I'm a little suspicious about the reverse$=r$ line when the Function is called reverse not reverse$, but that might be harmless. I generally don't mix the !%$ suffixes with the AS form.

How does it not work? Can we have some sample output.

Tom
MMBasic for Linux, Game*Mite, CMM2 Welcome Tape, Creaky old text adventures
 
Nimue

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Joined: 06/08/2020
Location: United Kingdom
Posts: 420
Posted: 01:52pm 22 Jan 2021
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  thwill said  Hi Nimue,

Unfortunately I'm not near my CMM2 so can't run it for myself.

I can't see an obvious pass-by-reference issue; reverse() doesn't do any "write operations" to in_string$.

I'm a little suspicious about the reverse$=r$ line when the Function is called reverse not reverse$, but that might be harmless. I generally don't mix the !%$ suffixes with the AS form.

How does it not work? Can we have some sample output.

Tom


What I get is "String too long".

If I add an extra print in the For Loop:

For i = 1 To 100
   Print i  ' Debug
   If Bin$(i) = reverse(Bin$(x)) Then
       If Hex$(i) = reverse(Hex$(i)) Then
           Print i,Bin$(i), Hex$(i)
       EndIf
   EndIf
Next i


I get:
1
1
1
1
1
1
1
etc
etc with the loop not incrementing until the string error.

Exactly the same happened before on a project where passing was the issue IIRC.

The reverse function works well on its own:

print reverse("Nimue") produces the desired output of a reversed string.

N
Entropy is not what it used to be
 
matherp
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Joined: 11/12/2012
Location: United Kingdom
Posts: 10310
Posted: 01:56pm 22 Jan 2021
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The first obvious bug is that i and r$ are global variables and are never re-initialised after the first time it is used. i in particular is buggered by the subroutine

USE OPTION EXPLICIT!!!!!!!!!
 
thwill

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Joined: 16/09/2019
Location: United Kingdom
Posts: 4311
Posted: 01:58pm 22 Jan 2021
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  matherp said  The first obvious bug is that i and r$ are global variables and are never re-initialised after the first time it is used. i in particular is buggered by the subroutine

USE OPTION EXPLICIT!!!!!!!!!


That will be it ;-) That will teach me to ignore the obvious.

Edit: Languages with implicit declaration are a 'mare ... and personally I don't have anything good to say about languages with implicit typing.
Edited 2021-01-23 00:02 by thwill
MMBasic for Linux, Game*Mite, CMM2 Welcome Tape, Creaky old text adventures
 
jirsoft

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Joined: 18/09/2020
Location: Czech Republic
Posts: 533
Posted: 02:00pm 22 Jan 2021
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I'm missing the bold part.

Function reverse(in_string$) As string
  r$ = ""
  For i = Len(in_string$) To 1 Step -1
      b$=Mid$(in_string$,i,1)
      r$=r$+b$
  Next i
  reverse$=r$
End Function


For i = 1 To 100
  If Bin$(i) = reverse(Bin$(i)) Then
      If Hex$(i) = reverse(Hex$(i)) Then
          Print i,Bin$(i), Hex$(i)
      EndIf
  EndIf
Next i


Or simpler:

Function reverse(in_string$) As string
  reverse = ""
  For i = Len(in_string$) To 1 Step -1
      CAT reverse, Mid$(in_string$,i,1)
  Next i
End Function
Jiri
Napoleon Commander and SimplEd for CMM2 (GitHub),  CMM2.fun
 
thwill

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Joined: 16/09/2019
Location: United Kingdom
Posts: 4311
Posted: 02:05pm 22 Jan 2021
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  jirsoft said  Or simpler:
Function reverse(in_string$) As string
  reverse = ""
  For i = Len(in_string$) To 1 Step -1
      CAT reverse, Mid$(in_string$,i,1)
  Next i
End Function


Simpler, but wrong

- 'reverse' doesn't need setting to "", that is the default on entry.
- 'i' is an undeclared global as Peter said.

Tom
MMBasic for Linux, Game*Mite, CMM2 Welcome Tape, Creaky old text adventures
 
matherp
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Joined: 11/12/2012
Location: United Kingdom
Posts: 10310
Posted: 02:05pm 22 Jan 2021
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Function reverse(in_string$) As string
  local r$
  local i
  For i = Len(in_string$) To 1 Step -1
      b$=Mid$(in_string$,i,1)
      r$=r$+b$
  Next i
  reverse=r$
End Function


For i = 1 To 100
  If Bin$(i) = reverse(Bin$(i)) Then
      If Hex$(i) = reverse(Hex$(i)) Then
          Print i,Bin$(i), Hex$(i)
      EndIf
  EndIf
Next i
 
Nimue

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Joined: 06/08/2020
Location: United Kingdom
Posts: 420
Posted: 02:34pm 22 Jan 2021
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  matherp said  The first obvious bug is that i and r$ are global variables and are never re-initialised after the first time it is used. i in particular is buggered by the subroutine

USE OPTION EXPLICIT!!!!!!!!!


DOH!!!!
Entropy is not what it used to be
 
Nimue

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Joined: 06/08/2020
Location: United Kingdom
Posts: 420
Posted: 02:35pm 22 Jan 2021
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  matherp said  
Function reverse(in_string$) As string
  local r$
  local i
  For i = Len(in_string$) To 1 Step -1
      b$=Mid$(in_string$,i,1)
      r$=r$+b$
  Next i
  reverse=r$
End Function


For i = 1 To 100
  If Bin$(i) = reverse(Bin$(i)) Then
      If Hex$(i) = reverse(Hex$(i)) Then
          Print i,Bin$(i), Hex$(i)
      EndIf
  EndIf
Next i


Thank you all for the comments and tweaks -- my own sloppy habits from Python krept in!!.

Nim
Entropy is not what it used to be
 
Nimue

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Joined: 06/08/2020
Location: United Kingdom
Posts: 420
Posted: 12:24pm 23 Jan 2021
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Thank you for your help on this the other day.

I use my CMM2 to indulge my hobby of working on number sequences:  https://oeis.org/A340559 << where you will see that I have added MM Basic solution to this sequence.

Cheers
Nim
Entropy is not what it used to be
 
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