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  • Cutting down on SELECT CASE options?

    When using a SELECT CASE statement, is there a way to call it
    back to itself? In other words, suppose I have the variable
    SayThis, which contains a number of zero to 10,000. The way I
    am watching my program work in the step by step, SELECT CASE is
    checking every possibility, rather than avoiding some of them.
    If SayThis = 9,999, then nearly every possibility is checked.
    I.e.,

    SELECT CASE SayThis
    Case 0: Print “What do you want me to say?”
    Case 1: print “Hello there, my name is Simon.”
    Case 2: Print “What is your name?”
    {{{and so on for 10,000 different statements}}}

    I am wondering, could we speed that up? Will/should something
    like this work?

    SELECT CASE SayThis
    Case 0 – 499
    SELECT CASE SayThis
    Case 0 – 99
    Select case SayThis
    Case 0: Print “What do you want me to say?”
    Case 1: print “Hello there, my name is Simon.”
    { rest of statements }
    End Select
    Case 100 - 199
    Select Case SayThis
    Case 100:Print “What is the name of your pet?”
    { rest of statements }
    End Select
    { rest of case options up to 499 }
    End select
    {rest of case options up to 10,000}
    End Select

    If it won’t work like this, can anyone suggest an alternative
    perhaps? The computer this will eventually be used on was
    assembled from the DOS days.

    On my computer, the delay while it checks for the case is not
    noticeable- but I wonder if it will be on a slower computer?
    That is why I was hoping to find a way to cut down on the
    options it has to check.

    Thank you.

    Robert


    ------------------

  • #2
    You could try using SELECT CASE AS LONG to get a speed up using
    a jump table.

    There are a number of other ways to do it. Probably the most
    straightfoward according to what you asked is embedded SELECT CASES.
    Code:
    SELECT CASE SomeValue
      CASE 0 to 99
        SELECT CASE SomeValue
          CASE 0 TO 9
            SELECT CASE SomeValue
              CASE 1:PRINT "Say This"
              CASE 2:PRINT "Say That"
          CASE 11 TO 19
            SELECT CASE SomeValue
              CASE 11:PRINT "Say This"
              CASE 12:PRINT "Say That"
            END SELECT
        END SELECT
    END SELECT
    You could also use ON x GOTO

    Though the best way would be to store all your strings in an array
    and reference them with their subscript. No SELECT CASE required!

    PRINT SayArray(127)


    ------------------
    Every day I try to learn one thing new,
    but new things to learn are increasing exponentially.
    At this rate I’m becoming an idiot faster and faster !!!
    ------------------
    George W. Bleck
    Lead Computer Systems Engineer
    KeySpan Corporation
    My Email

    [This message has been edited by George Bleck (edited May 13, 2003).]
    <b>George W. Bleck</b>
    <img src='http://www.blecktech.com/myemail.gif'>

    Comment


    • #3
      > You could try using SELECT CASE AS LONG

      Nope, not in PB/DOS you can't.

      Robert, by far the fastest way to do a complex selection with PB/DOS is ON GOTO.

      -- Eric


      ------------------
      Perfect Sync Development Tools
      Perfect Sync Web Site
      Contact Us: mailto:[email protected][email protected]</A>



      [This message has been edited by Eric Pearson (edited May 13, 2003).]
      "Not my circus, not my monkeys."

      Comment


      • #4
        Whoops...forgot which forum section this is

        I stand corrected, Eric is on the money.

        ------------------
        Every day I try to learn one thing new,
        but new things to learn are increasing exponentially.
        At this rate I’m becoming an idiot faster and faster !!!
        ------------------
        George W. Bleck
        Lead Computer Systems Engineer
        KeySpan Corporation
        My Email

        [This message has been edited by George Bleck (edited May 13, 2003).]
        <b>George W. Bleck</b>
        <img src='http://www.blecktech.com/myemail.gif'>

        Comment


        • #5
          ON n GOTO is the fastest way, but the range of n is only 0-255. Arrays are also fast, but with so many elemenets you will need to use virtual arrays. I think a good choice will be put the strings in a random file. The access is fast and you don't waste precious DOS memory.


          ------------------

          Comment


          • #6
            With many choices, always put the more likely first in the test list.

            MCM
            Michael Mattias
            Tal Systems Inc. (retired)
            Racine WI USA
            [email protected]
            http://www.talsystems.com

            Comment


            • #7
              Originally posted by Michael Mattias:
              ...always put the more likely first...
              Put another way: (paraphrasing) Occam's Razor: All other qualities
              being equal, the simplest choice tends to be the best and most
              reliable.


              ------------------
              There are no atheists in a fox hole or the morning of a math test.
              If my flag offends you, I'll help you pack.

              Comment


              • #8


                That's also

                Put another way: (paraphrasing) Occam's Razor: All other qualities
                being equal, the simplest choice tends to be the best and most
                reliable.
                an argument for portability if you happen to need it.



                ------------------
                Mike Luther
                [email protected]
                Mike Luther
                [email protected]

                Comment


                • #9
                  Your example implies an attempt to emulate the classic "Simon Says" program that has been around since the first Apple Computers were introduced. Unless there is more to it than you have revealed, I don't see how equating text strings to a flat list of integers is going to make Simon very wise or engaging.

                  I have no links to offer, but I know that Simon Says source in BASIC used to be listed in a lot of BBS sites.

                  ------------------
                  Jim C.
                  Jim C.

                  Comment


                  • #10
                    SELECT CASE is checking every possibility, rather than avoiding some of them.
                    Call me old-fashioned, but if it didn't do this, I think I might go so far as to suggest it's a bug.

                    MCM

                    Michael Mattias
                    Tal Systems Inc. (retired)
                    Racine WI USA
                    [email protected]
                    http://www.talsystems.com

                    Comment


                    • #11
                      Originally posted by Michael Mattias:
                      Call me old-fashioned, but if it didn't do this, I think I might go so far as to suggest it's a bug.

                      MCM

                      Michael, well, maybe it IS the way it is supposed to work. My
                      training of CASE statements is once the CASE is carried out,
                      it gets out of the Select statement. I.e., if
                      Code:
                      Select case OptionNo
                          case 1:Filename$="C:\game\part1.exe"
                          case 2:Filename$="C:\game\part2.exe"
                          case 3:Filename$="C:\game\part3.exe"
                          case 4:Filename$="C:\game\part4.exe"
                          case 5:Filename$="C:\game\part5.exe"
                      '     etc. etc.
                      END SELECT
                      What I am saying is supposed OptionNo is = 2. It finds case
                      number two, sets the value of Filename$ to "C:\game\part2.exe"
                      just fine. But it goes on to check case 3, case 4, etc. I
                      thought once it found a case, it executed the statements for
                      that case, and goes to END SELECT.


                      Jim- You are right. This is really for another program, but I
                      a have program of asking questions clearly. Let me try anyway.
                      Is the above example better?

                      [This message has been edited by Robert Carneal (edited May 20, 2003).]

                      Comment


                      • #12
                        Read the manual:

                        "As soon as an evaluation is TRUE (non-zero), the statements following that CASE clause are executed, up to the next CASE clause.
                        Execution then passes to the statement following the END SELECT statement. If none of the evaluations is TRUE, the statements following the optional CASE ELSE clause are executed."

                        But until it founds the item, it must check every case instruction to see if it meets the requirements expressed in SELECT CASE.



                        ------------------

                        Comment


                        • #13
                          2. It finds case number two, sets the value of Filename$ to "C:\game\part2.exe"
                          just fine. But it goes on to check case 3, case 4, etc.
                          You are suggesting the compiler generates code to test every case, doing nothing if the test has already been met?

                          If that's true ... that's a bad bug in the compiler which surely would hav been detected in the ten-plus years PB/DOS compilers have been available.

                          I'd suspect some quirk in the stepping debugger; but I think you need to bundle up your source code and send it to pb support along with an explanation.


                          MCM



                          [This message has been edited by Michael Mattias (edited May 21, 2003).]
                          Michael Mattias
                          Tal Systems Inc. (retired)
                          Racine WI USA
                          [email protected]
                          http://www.talsystems.com

                          Comment


                          • #14
                            PowerBASIC definitely does NOT work like that, so if Robert has code that exhibits that symptom, then I would realy suspect some other problem exists in the code (such as memory corruption, etc).

                            Adding $ERROR ALL ON can help locate the most common cause:- accessing an array past its bounds.

                            ------------------
                            Lance
                            PowerBASIC Support
                            mailto:[email protected][email protected]</A>
                            Lance
                            mailto:[email protected]

                            Comment


                            • #15
                              Originally posted by Lance Edmonds:
                              if Robert has code that exhibits that symptom, then I would realy suspect some other problem exists in the code (such as memory corruption, etc).

                              Adding $ERROR ALL ON can help locate the most common cause:- accessing an array past its bounds.

                              I think I am getting somewhere now. I have been using the
                              debugger and going step-by-step, line-by-line, etc., and it is
                              this time I notice it checking through all CASE statements,
                              even beyond the one that fit the criteria. I want it to stop
                              checking the CASE after finding the correct one, hence my
                              desire for something that behaved like embedded SELECT CASE
                              originally.

                              I currently do not have $ERROR ALL ON. I will try that
                              and report what result I do have. I do have 384M of memory, and
                              just have not felt like adding more memory due to a new computer
                              arriving in a few weeks.

                              This is off this particular topic, but the speaking of the new
                              computer- it will have Windows XP Pro. I can still use DOS
                              Powerbasic in a DOS screen/box in XP, correct?

                              Thank you.

                              Robert

                              ------------------

                              Comment


                              • #16
                                I can still use DOS Powerbasic in a DOS screen/box in XP, correct?
                                Sure.

                                ------------------
                                Tom Hanlin
                                PowerBASIC Staff

                                Comment


                                • #17
                                  If you put EXIT SELECT in each CASE, will it still do that?

                                  ------------------


                                  [This message has been edited by Jerry Fielden (edited May 21, 2003).]

                                  Comment


                                  • #18
                                    Originally posted by Jerry Fielden:
                                    If you put EXIT SELECT in each CASE, will it still do that?

                                    I had to go back and check. BRAVO! No it will not do that after putting EXIT SELECT in each CASE.

                                    I should have known since I use EXIT IF and EXIT FOR. I guess
                                    I forgot EXIT SELECT was available.

                                    Thank you.

                                    Robert

                                    ------------------

                                    Comment


                                    • #19
                                      Not needed, Robert. CASE checking is only done until a match is found. If
                                      stepping the code through the debugger suggests otherwise, it's just a
                                      side-effect of how the debugger works.


                                      ------------------
                                      Tom Hanlin
                                      PowerBASIC Staff

                                      Comment


                                      • #20
                                        Greetings --

                                        This was just a thought --

                                        Code:
                                        Ziz$=Str$(OptionNo)
                                        Ziz$=Trim$(Ziz$)
                                        IF OptionNo<100 THEN Ziz$="0"+Ziz$:' These 2 IF lines are optional
                                        IF OptionNo<10 THEN Ziz$="00"+Ziz$:' Just depends on user needs
                                        Select case OptionNo
                                            case 1 to 100
                                                 Filename$="C:\game\part"+Ziz$+".exe"
                                        End Select
                                        Thanx-A-Lot and Enjoy, Frank -- My PB


                                        [This message has been edited by Frank Ferrell (edited June 21, 2003).]

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