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Newsgroups: fido.science
Distribution: fido
From: DAVID WILLIAMS 
Date: Fri, 13 Aug 04 08:13:42 +0200
Subject: Pythagorean triples
Message-ID: 
Organization: The Bayman BBS,Toronto, (416)698-6573 - 1:250/514
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Xref: number1.nntp.dca.giganews.com fido.science:310

->  DW> ->      SUB Delay (t%) 
 
->  DW> ->         StopTime& = TIMER + t% 
->  DW> ->         DO 
->  DW> ->            IF LEN(INKEY$) THEN EXIT DO 
->  DW> ->         LOOP UNTIL (StopTime& - TIMER) MOD 86400 <= 0 
 
->  DW> ->      END SUB 
 
->  DW> I usually use rather simpler code: 
 
-> good! because that code fails at midnight. 
  
Maybe. I'm not sure. I never use MOD with negative numbers. The way 
BASIC does it doesn't make sense to me. I figure that -5 MOD 3 should 
come to 1, since the next-lower multiple of 3 is -6, and -5 is 1 more 
than that. But BASIC says it's -2, or something. I think it's related 
to FIX, which I also almost never use. 
  
It makes good sense to me to write: 
  
SUB Delay(D!) 
  T! = TIMER 
  DO 
    IF TIMER < T! THEN T! = T! - 86400 
    IF LEN(INKEY$) THEN EXIT DO 
  LOOP UNTIL TIMER >= T! + D! 
END SUB 
  
At midnight, TIMER jumps backward by 86400 seconds, so this code just 
makes T! jump back by the same amount, so they keep the same 
relationship to each other. Of course, this makes T! have a negative 
value, but that doesn't matter. 
  
-> I do it this way to avoid arithmetic and the need to consider roll-over at 
-> midnight. 
 
-> sub delay (s) 
->     for x=1 to s*18.6 
->      t=timer 
->      while t=timer 
->      if inkey$  "" goto done 
->      wend 
->     next 
->   done: 
-> end sub 
 
-> Jasen 
  
Isn't "s*18.6" arithmetic? 
  
More seriously - in some BASICs - you make it jump out of the loop if a 
key is pressed, without cleaning the FOR... information off the stack. 
Some BASICs will sort this out for you, but others won't, and will lead 
you into all kinds of tangles later. It would be better to use EXIT FOR 
than the GOTO. 
  
My $0.02 worth. 
  
                         dow