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Question on Booleans and string passing

 
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victorf



Joined: 01 Jan 2006
Posts: 342
Location: Schenectady, New York
Posted: 29 January 2006, 20:52 PM    Post subject: Question on Booleans and string passing Reply with quote
Here are 3 questions

1. If UserFldElUnits is defined as

Code:

dim UserFldElUnits as Boolean

Is this a legal statement:

  if UserFldElUnits then
    Call PutLine(CStr(UserFldEl) + " Ft/Min")
  else
    Call PutLine (CStr(UserFldEl) + " M/Min")
  End if


or do I have to say:

Code:

  if UserFldElUnits = True then
    Call PutLine(CStr(UserFldEl) + " Ft/Min")
  else
    Call PutLine (CStr(UserFldEl) + " M/Min")
  End if

2. If subroutine PutLine is defined:
Code:

      Sub PutLine(ByRef InBuf as String)

can the string be passed as I show above?

3. can a CByte() be used to convert a Boolean to a
byte?

Any enlightenment will be appreciated. Smile

Vic
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mikep



Joined: 24 Sep 2005
Posts: 765
Location: Austin, TX
Posted: 29 January 2006, 23:05 PM    Post subject: Reply with quote
My first response would be "what does the compiler say about this code". So that's what I tried and here are your answers:

1. The '= true' is implicit and is not needed. However strings are concatentatred using the & operator - not the + operator. See section 2.4.6 of the manual: http://www.zbasic.net/doc/ZBasicRef/ZBasicRef25.html

2. No - you need to assign the result to a variable and pass that variable into the function call. If not you get a compiler error about invalid use of expression for a ByRef parameter. Remember ByVal passes the value on the stack which can either be an intermediate expression or from a variable and ByRef passes a reference which is the address of a variable. See section 2.14 of the manual http://www.zbasic.net/doc/ZBasicRef/ZBasicRef45.html

3. This page from the reference manual should answer your question: http://www.zbasic.net/doc/ZBasicSysLib/ZBasicSysLib30.html.
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victorf



Joined: 01 Jan 2006
Posts: 342
Location: Schenectady, New York
Posted: 31 January 2006, 1:42 AM    Post subject: Reply with quote
Quote:

1. The '= true' is implicit and is not needed. However strings are concatentatred using the & operator - not the + operator. See section 2.4.6 of the manual: http://www.zbasic.net/doc/ZBasicRef/ZBasicRef25.html


Sorry, I had my Pascal hat on I guess Confused
Quote:

2. No - you need to assign the result to a variable and pass that variable into the function call.

I think I knew this but was hoping Smile I could get away with my way just to save declaring a variable in the subroutine that the expression came from.

Anyway, thank you for taking the time to respond to my questions.

Vic
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spamiam



Joined: 13 Nov 2005
Posts: 661
Posted: 31 January 2006, 14:46 PM    Post subject: Reply with quote
victorf wrote:
...was hoping Smile I could get away with my way just to save declaring a variable in the subroutine that the expression came from.


I would have tried to pass a concatenation just the way you did (using the & operator of course). In some dialects of BASIC it probably will work the way you intended.

I guess this is not one of them.

-Tony
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mikep



Joined: 24 Sep 2005
Posts: 765
Location: Austin, TX
Posted: 31 January 2006, 16:37 PM    Post subject: Reply with quote
spamiam wrote:
I would have tried to pass a concatenation just the way you did (using the & operator of course). In some dialects of BASIC it probably will work the way you intended.

I guess this is not one of them.

Less sophisticated versions of Basic may only support ByVal parameters, so this will always work. However they don't support arrays for example that need to be passed by reference.

ZBasic is based on Microsoft's Visual Basic and supports both ByVal and ByRef parameters. In other languages that you may be more used to such as C these are passing parameters by value and by address. In any case it is important to match the type otherwise you will get garbage. The checking in ZBasic will tell you when you have made an error as it did this in case.

Of course another way for Vic to change his solution is to have PutLine subroutine take a ByVal string parameter but there are pros and cons to this approach depending on the rest of his program.
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dkinzer
Site Admin


Joined: 03 Sep 2005
Posts: 2493
Location: Portland, OR
Posted: 01 February 2006, 16:49 PM    Post subject: Reply with quote
Quote:
I think I knew this but was hoping I could get away with my way just to save declaring a variable in the subroutine that the expression came from.


Parameter passing 'ByRef' is implemented by passing the address of the referent variable to the procedure. The compiler could support the passing of a value other than a variable by automatically creating a temporary variable to hold the value and then passing the address of the temp. Although BasicX doesn't support this, it appears that VB does.
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