simple Syntax question IF THEN ELSE

tochus

hello i have a simple question about pbasic using if then else statement.
i learned C ++ about if then else, they can use a ( ) including the statement, i wonder if the pbasic can do this.
also, if i want to compare on statement then execute three or more action what can i do. for instance,
IF distance > 10 and IRdetect = 0·THEN
{
·GOSUB FORWARD
·COUNTER = COUNTER + 1
·BALLFOUND = 1
}
ENDIF

SOMETHING LIKE THIS, HOW CAN I DO THIS.
THANKS FOR REPLYING
·

Jon Williams

You were close -- just drop the curly braces.

IF (distance > 10) AND (IRdetect = 0) THEN
  GOSUB Forward
  counter = counter + 1
  ballFound = 1
ENDIF

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Jon Williams
Applications Engineer, Parallax
Dallas Office

tochus

what is the difference between elseif and if?
i have wrote the following code
····· ELSEIF (counter =< 8 AND ultdis > 50 ) THEN············· ' check if the robot turn 360
····· GOSUB right
····· DEBUG ? counter·· ,CR·································· 'debug = printscreen
····· counter = counter + 1
····· ELSEIF (counter > 8 AND ultdis > 50 ) THEN··············· ' check if the robot turn 360
····· GOSUB forward

i wonder if the first elseif statement execute the following three statement. thanks so much for your reply
i really appreciate it.

Jon Williams

With ELSEIF you can create compound decision structures -- be careful though, you can create problems for yourself it they get to unwieldy.·

IF (condition1) THEN
  ' do something #1
ELSEIF (condition2) THEN
  ' do something #2
ELSE
  ' do something else
ENDIF

If condition1 evaluates as true, then "do something #1" will execute, otherwise condition2 will be evaluated.· If condition2 is true, then "do something #2" will run, otherwise "do something else" will run.


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Jon Williams
Applications Engineer, Parallax
Dallas Office

tochus

can i write it in this way? I wonder if the second if statement process the following three statement?

thanks for reply



IF ( ballgotten = 1) THEN
····· ballgotten = 0
······· IF ( changedirection = 1) THEN
······· GOSUB right
······· changedirection = 0
······· counter = counter + 1
······· ENDIF
····· ENDIF

allanlane5

Yes, your nested 'IF' should work correctly -- and I find it MUCH easier to follow than that 'ELSEIF' construct.

Jon Williams

Yes, that will work. I also agree with Allan and tend not to use ELSEIF as things can become a bit unwieldy if you're not careful.

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Jon Williams
Applications Engineer, Parallax
Dallas Office

Tracy Allen

ELSEIF is a straightforward way to deal with a cascade of conditions, when a SELECT-CASE statement is not quite suitable. You have to remember that ELSEIF is in fact part of the ELSE clause, executed when the original condition is not true.

IF condxA THEN
  statementsA
ELSEIF condxB THEN
  statementsB
ELSEIF condxC THEN
  statementsC
ELSE
  statememtsD
ENDIF

The ELSEIF clause is only executed if condxA is false. Then, if condxB is true, none of the other following ELSEIF or ELSE clauses will be executed and it drops right through to the ENDIF.

The ELSEIF could be written as nested IFs, but in my opinion it is more prone to error and confusion:

IF condxA THEN
  statementsA
ELSE
  IF condxB THEN
    statementsB
  ELSE
    IF condxC THEN
      statementsC
    ELSE
      statememtsD
    ENDIF
  ENDIF
ENDIF

I think that comes out the same?

I have a web page that explores how the compiler translates from PBASIC 2.5 back to the more primitive PBASIC 2.0. The old PBASIC (for you lucky newcomers!) had only the statement,
IF condx THEN label
The URL is:
www.emesystems.com/BS2pbasic25.htm
I have found that it often helps resolve confusion, to see how the translation is implemented under the hood in a few example programs. The form "IF condx THEN label" is never ambiguous! Spagetti, yes, ambiguous, no.

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Tracy Allen
www.emesystems.com