IF...ELSEIF problem

Robert Schwartz · 2005-02-06 04:59

I am currently working on a robotics project and I need to use an if elseif statement. The segemnt of code I am using is:

IF (Close_Right = 1) THEN CloseRight
ELSEIF (Close_Left = 1) THEN CloseLeft
ELSEIF (Far_Right = 1) THEN FarRight
ELSEIF (Far_Left = 1) THEN FarLeft
ELSE GiveUp
ENDIF

All of the variables are initialized and all of the labels have contents, but I get the error, "'ELSEIF' must be preceded by 'IF'" whenever I try to tokenize it. What is the matter with my syntax? Thank You.

Robert Schwartz · 2005-02-06 05:17

Problem fixed. Added Goto's before function calls.

Jon Williams · 2005-02-06 14:40

Let me suggest a small style change that will help your program be more readable -- and discover errors like you originally encountered.· When doing anything more than a sing IF-THEN-Label, form your code like this:

IF (Close_Right = 1) THEN 
  GOTO CloseRight
ELSEIF (Close_Left = 1) THEN 
  GOTO CloseLeft
ELSEIF (Far_Right = 1) THEN 
  GOTO FarRight
ELSEIF (Far_Left = 1) THEN 
  GOTO FarLeft
ELSE 
  GOTO GiveUp
ENDIF

It doesn't take much more typing, and it does make the structure easier to read.

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Jon Williams
Applications Engineer, Parallax
Dallas, TX· USA

Robert Schwartz · 2005-02-06 21:44

Before I fixed the problem, I had it that way, but I got a missing ":" error, so I changed it to the one-line form. Thanks for the advice though.

Jondice · 2005-04-07 03:38

Jon Williams said...
Let me suggest a small style change that will help your program be more readable -- and discover errors like you originally encountered. When doing anything more than a sing IF-THEN-Label, form your code like this:
IF (Close_Right = 1) THEN  

  GOTO CloseRight
ELSEIF (Close_Left = 1) THEN  

  GOTO CloseLeft
ELSEIF (Far_Right = 1) THEN  

  GOTO FarRight
ELSEIF (Far_Left = 1) THEN  

  GOTO FarLeft
ELSE  

  GOTO GiveUp
ENDIF 
It doesn't take much more typing, and it does make the structure easier to read.

It would appear as though this style is now enforced by the parser

allanlane5 · 2005-04-07 15:51

Yes, actually the
IF (CloseRight=1) THEN CloseRight

is a 'single line version' of the IF statement -- the statement ends with the line-feed.

Thus:
IF (xyz) THEN GoToTarget
ELSEIF (abc) THEN GoToAnotherTarget
' The ELSEIF actually has no 'IF' in front of it,
' since the single-line IF is already done.

The equivalent for your code is:
IF (Close_Right = 1) THEN CloseRight
IF (Close_Left = 1) THEN CloseLeft
IF (Far_Right = 1) THEN FarRight
IF (Far_Left = 1) THEN FarLeft
GOTO GiveUp

Thus you don't need the ELSEIF construct -- it's already built into the code flow.

IF...ELSEIF problem

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