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PBASIC syntax question (IF THEN) — Parallax Forums

PBASIC syntax question (IF THEN)

ArchiverArchiver Posts: 46,084
edited 2004-03-29 22:16 in General Discussion
In the new PBASIC, I don't think there is ELSEIF.
Thus, is this allowable?

1. IF IN0=0 THEN
'statement
ELSE
IF IN1=0 THEN
'statement
ELSE
'statement
ENDIF
ENDIF

2. Is there a limit to how many times I can nest a IF THEN ELSE
inside a ELSE (above example has 1 nested)?

3. Is there a better way of doing ELSEIF?

Thank you.

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2004-03-29 15:53
    You are not correct; ELSEIF is available in PBASIC 2.5. It only takes
    opening the help file to find out....

    That said, you have a logic flaw in your code below. Why? Because an
    input pin can have one of two states, yet your logic below accommodates
    three conditions.

    For demonstration, here's where one might use ELSEIF:

    IF (temp < 68) THEN
    CoolerCtrl = IsOff
    HeaterCtrl = IsOn
    ELSEIF (temp > 78) THEN
    HeaterCtrl = IsOff
    AcCtrl = IsOn
    ELSE
    HeaterCtrl = IsOff
    AcCtrl = IsOff
    ENDIF

    This can get a bit messy (when testing a single variable), so
    SELECT-CASE might provide cleaner coding:

    SELECT temp
    CASE < 68
    CoolerCtrl = IsOff
    HeaterCtrl = IsOn
    CASE > 78
    CoolerCtrl = IsOn
    HeaterCtrl = IsOff
    ELSE
    CoolerCtrl = IsOff
    HeaterCtrl = IsOff
    ENDSELECT

    Suggestion: When testing a single variable for complex conditions, use
    SELECT-CASE. When two or more variables are part of the test,
    IF-THEN-ELSE is the proper choice.

    -- Jon Williams
    -- Applications Engineer, Parallax
    -- Dallas Office

    Original Message
    From: basicstampede [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=fifOufTM5Cq6suXSlQ-e4FwwjcIGgway0g7AuW9naD0OuanVaGp_yeMV4Vb1sbcwEXloDjX6TCMhE3pWtEs1Org]basicstampede@y...[/url
    Sent: Monday, March 29, 2004 8:34 AM
    To: basicstamps@yahoogroups.com
    Subject: [noparse][[/noparse]basicstamps] PBASIC syntax question (IF THEN)


    In the new PBASIC, I don't think there is ELSEIF.
    Thus, is this allowable?

    1. IF IN0=0 THEN
    'statement
    ELSE
    IF IN1=0 THEN
    'statement
    ELSE
    'statement
    ENDIF
    ENDIF

    2. Is there a limit to how many times I can nest a IF THEN ELSE
    inside a ELSE (above example has 1 nested)?

    3. Is there a better way of doing ELSEIF?

    Thank you.
  • ArchiverArchiver Posts: 46,084
    edited 2004-03-29 18:03
    Yes, as Jon pointed out, there is in fact a handy ELSEIF option.
    Your specific example could be coded as,

    IF IN0=0 THEN
    'statement1
    ELSEIF IN1=0 THEN 'statement2
    ELSE
    'statement3
    ENDIF

    In this case, statement 1 is executed if in0=0, regardless of the
    state of in1. If in1=1, and in2=0, then statement2 is executed, and
    finally, statement3 is executed iff both in0=1 and in1=1. Is that
    your intent?

    With regard to your second question, I don't think there is any limit
    for nesting the IF-THEN-ELSEIF-ELSE-ENDIF constructs. PBASIC under
    the hood resolves those to simple IF-THEN-GOTO statements. See
    <http://www.emesystems.com/BS2pbasic25.htm> for more exploration of
    that issue.

    The logic above is kind of hard to follow, because the conditions are
    spread out over several statements. Jon mentioned SELECT-CASE which
    can make the logic crystal clear. Here is another option:

    ON inA&%11 GOTO statement1, statement1, statement2, statement3

    That is more clear in my mind because the 4 possible input states,
    00, 01, 10 and 11, and the actions that follow are laid out in one
    structure. It results in smaller faster code than the IF-THEN, too.
    Under the PBASIC hood, the ON--GOTO is resolved simply to:

    BRANCH inA&%11, [noparse][[/noparse] statement1, statement1, statement2, statement3 ]


    -- regards,
    Tracy



    >In the new PBASIC, I don't think there is ELSEIF.
    >Thus, is this allowable?
    >
    >1. IF IN0=0 THEN
    > 'statement
    > ELSE
    > IF IN1=0 THEN
    > 'statement
    > ELSE
    > 'statement
    > ENDIF
    > ENDIF
    >
    >2. Is there a limit to how many times I can nest a IF THEN ELSE
    >inside a ELSE (above example has 1 nested)?
    >
    >3. Is there a better way of doing ELSEIF?
  • ArchiverArchiver Posts: 46,084
    edited 2004-03-29 18:17
    Oops, the second sentence should read,

    "If in0=1, and in1=0, then statement2 is executed".


    > IF IN0=0 THEN
    > 'statement1
    > ELSEIF IN1=0 THEN 'statement2
    > ELSE
    > 'statement3
    > ENDIF
    >
    >In this case, statement 1 is executed if in0=0, regardless of the
    >state of in1. If in1=1, and in2=0, then statement2 is executed, and
    >finally, statement3 is executed iff both in0=1 and in1=1. Is that
    >your intent?
  • ArchiverArchiver Posts: 46,084
    edited 2004-03-29 20:34
    Jon, thanks for the info.

    Actually, I could not find ELSEIF in the help section. I use editor
    2.0 and 2.1, and neither has ELSEIF in the help section. Where are
    you finding it?

    Thank you.



    --- In basicstamps@yahoogroups.com, "Jon Williams" <jwilliams@p...>
    wrote:
    > You are not correct; ELSEIF is available in PBASIC 2.5. It only
    takes
    > opening the help file to find out....
    >
    > That said, you have a logic flaw in your code below. Why? Because
    an
    > input pin can have one of two states, yet your logic below
    accommodates
    > three conditions.
    >
    > For demonstration, here's where one might use ELSEIF:
    >
    > IF (temp < 68) THEN
    > CoolerCtrl = IsOff
    > HeaterCtrl = IsOn
    > ELSEIF (temp > 78) THEN
    > HeaterCtrl = IsOff
    > AcCtrl = IsOn
    > ELSE
    > HeaterCtrl = IsOff
    > AcCtrl = IsOff
    > ENDIF
    >
    > This can get a bit messy (when testing a single variable), so
    > SELECT-CASE might provide cleaner coding:
    >
    > SELECT temp
    > CASE < 68
    > CoolerCtrl = IsOff
    > HeaterCtrl = IsOn
    > CASE > 78
    > CoolerCtrl = IsOn
    > HeaterCtrl = IsOff
    > ELSE
    > CoolerCtrl = IsOff
    > HeaterCtrl = IsOff
    > ENDSELECT
    >
    > Suggestion: When testing a single variable for complex conditions,
    use
    > SELECT-CASE. When two or more variables are part of the test,
    > IF-THEN-ELSE is the proper choice.
    >
    > -- Jon Williams
    > -- Applications Engineer, Parallax
    > -- Dallas Office
    >
    >
    >
    Original Message
    > From: basicstampede [noparse][[/noparse]mailto:basicstampede@y...]
    > Sent: Monday, March 29, 2004 8:34 AM
    > To: basicstamps@yahoogroups.com
    > Subject: [noparse][[/noparse]basicstamps] PBASIC syntax question (IF THEN)
    >
    >
    > In the new PBASIC, I don't think there is ELSEIF.
    > Thus, is this allowable?
    >
    > 1. IF IN0=0 THEN
    > 'statement
    > ELSE
    > IF IN1=0 THEN
    > 'statement
    > ELSE
    > 'statement
    > ENDIF
    > ENDIF
    >
    > 2. Is there a limit to how many times I can nest a IF THEN ELSE
    > inside a ELSE (above example has 1 nested)?
    >
    > 3. Is there a better way of doing ELSEIF?
    >
    > Thank you.
  • ArchiverArchiver Posts: 46,084
    edited 2004-03-29 22:16
    If you put ELSEIF in the search window you will find it under the
    IF-THEN-ELSE explanation as it is part of that construct. I will updat
    the Help file so that it's easier to find.

    -- Jon Williams
    -- Parallax

    Original Message
    From: basicstampede [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=u_alm0fELch6QIlap8QQI84eUGsQC_HGGRCOIq9iizVQyp5mf4GVzKKo66beESpzHqtbjXeVjzL5HJc_Wj6Rew]basicstampede@y...[/url
    Sent: Monday, March 29, 2004 1:35 PM
    To: basicstamps@yahoogroups.com
    Subject: [noparse][[/noparse]basicstamps] Re: PBASIC syntax question (IF THEN)


    Jon, thanks for the info.

    Actually, I could not find ELSEIF in the help section. I use editor
    2.0 and 2.1, and neither has ELSEIF in the help section. Where are
    you finding it?

    Thank you.



    --- In basicstamps@yahoogroups.com, "Jon Williams" <jwilliams@p...>
    wrote:
    > You are not correct; ELSEIF is available in PBASIC 2.5. It only
    takes
    > opening the help file to find out....
    >
    > That said, you have a logic flaw in your code below. Why? Because
    an
    > input pin can have one of two states, yet your logic below
    accommodates
    > three conditions.
    >
    > For demonstration, here's where one might use ELSEIF:
    >
    > IF (temp < 68) THEN
    > CoolerCtrl = IsOff
    > HeaterCtrl = IsOn
    > ELSEIF (temp > 78) THEN
    > HeaterCtrl = IsOff
    > AcCtrl = IsOn
    > ELSE
    > HeaterCtrl = IsOff
    > AcCtrl = IsOff
    > ENDIF
    >
    > This can get a bit messy (when testing a single variable), so
    > SELECT-CASE might provide cleaner coding:
    >
    > SELECT temp
    > CASE < 68
    > CoolerCtrl = IsOff
    > HeaterCtrl = IsOn
    > CASE > 78
    > CoolerCtrl = IsOn
    > HeaterCtrl = IsOff
    > ELSE
    > CoolerCtrl = IsOff
    > HeaterCtrl = IsOff
    > ENDSELECT
    >
    > Suggestion: When testing a single variable for complex conditions,
    use
    > SELECT-CASE. When two or more variables are part of the test,
    > IF-THEN-ELSE is the proper choice.
    >
    > -- Jon Williams
    > -- Applications Engineer, Parallax
    > -- Dallas Office
    >
    >
    >
    Original Message
    > From: basicstampede [noparse][[/noparse]mailto:basicstampede@y...]
    > Sent: Monday, March 29, 2004 8:34 AM
    > To: basicstamps@yahoogroups.com
    > Subject: [noparse][[/noparse]basicstamps] PBASIC syntax question (IF THEN)
    >
    >
    > In the new PBASIC, I don't think there is ELSEIF.
    > Thus, is this allowable?
    >
    > 1. IF IN0=0 THEN
    > 'statement
    > ELSE
    > IF IN1=0 THEN
    > 'statement
    > ELSE
    > 'statement
    > ENDIF
    > ENDIF
    >
    > 2. Is there a limit to how many times I can nest a IF THEN ELSE
    > inside a ELSE (above example has 1 nested)?
    >
    > 3. Is there a better way of doing ELSEIF?
    >
    > Thank you.



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