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Active Forums => QB64 Discussion => Topic started by: SMcNeill on December 24, 2020, 03:27:06 pm

Title: Bplus will like this one...
Post by: SMcNeill on December 24, 2020, 03:27:06 pm
I was working around on working up a custom calendar for 2021, for my PC, and a light bulb lit up over my head.  Last year, when we were sorting out whether a year was a leap year, or not, me and Bplus worked for a week or more to debug the ExtendedTimer routine.

We didn't have to, thanks to already existing code which we had in our toolbox, that we were too blind to use...

/SIGH!!   It's the story of my life -- spend forever to do something the hard way, and then POOF turn around a little while later and realize it was sooooo simple to begin with.  It's like rewiring a whole house, when all you needed to do was flip on the light switch to turn on the lights in the kitchen.

I present to you, IsLeapYear, in its simplest form:

Code: QB64: [Select]
  1. SCREEN _NEWIMAGE(1200, 720, 32)
  2.  
  3. FOR i = 1900 TO 2036
  4.     PRINT i, IsLeapYear(i),
  6.  
  7.  
  8.  
  9. FUNCTION IsLeapYear (yyyy) 'use 4 digit year
  10.     IF GetDay(2, 29, yyyy) <> GetDay(3, 1, yyyy) THEN IsLeapYear = -1
  12.  
  13. FUNCTION GetDay (m, d, y) 'use 4 digit year
  14.     'From Zeller's congruence: https://en.wikipedia.org/wiki/Zeller%27s_congruence
  15.     mm = m: dd = d: yyyy = y
  16.     IF mm < 3 THEN mm = mm + 12: yyyy = yyyy - 1
  17.     century = yyyy MOD 100
  18.     zerocentury = yyyy \ 100
  19.     result = (dd + INT(13 * (mm + 1) / 5) + century + INT(century / 4) + INT(zerocentury / 4) + 5 * zerocentury) MOD 7
  20.     IF result = 0 THEN
  21.         GetDay = 7
  22.     ELSE
  23.         GetDay = result
  24.     END IF
  25.     'Function changed to return a numeric value instead of a string for this program
  26.     '    SELECT CASE result
  27.     '        CASE 7: GetDay$ = "Saturday"
  28.     '        CASE 1: GetDay$ = "Sunday"
  29.     '        CASE 2: GetDay$ = "Monday"
  30.     '        CASE 3: GetDay$ = "Tuesday"
  31.     '        CASE 4: GetDay$ = "Wednesday"
  32.     '        CASE 5: GetDay$ = "Thursday"
  33.     '        CASE 6: GetDay$ = "Friday"
  34.     '    END SELECT
  36.  

We had a routine to get the day of the week, from any given date, and it's been working FOREVER AND EVER!!  As long as the 29th isn't the same day as the 1st of the next month, we have a leap year.  Otherwise, we don't...

One line logic, with no need to do math for mod 4, /400 but not 2000, except when - 29.6 or multiplied by 13.25...

Now, the question is:  Why didn't anyone point out how simple this logic is to us back then??  :P
Title: Re: Bplus will like this one...
Post by: STxAxTIC on December 24, 2020, 04:15:08 pm
Just a comment. A completely unnecessary one, cause the code speaks for itself.

This isn't really lone-line logic, though, right? Otherwise the whole program would be one line. You still have to do the hard part of filtering out the leap year cases by *some* calculation, its just in a different function now.

Never mind me though, carry on!


Title: Re: Bplus will like this one...
Post by: SpriggsySpriggs on December 24, 2020, 04:20:38 pm
This reminds me of code I had for checking the amount of days between two dates. It had a function for determining leap year as well.
EDIT: I removed the other unnecessary code because you are focusing on leap years.

Code: QB64: [Select]
  4.  
  5. DIM i
  6. FOR i = 1900 TO 2036
  7.     PRINT i, check_leap_year(i)
  10.  
  11. FUNCTION check_leap_year (year AS LONG)
  12.     IF year MOD 4 = 0 AND year MOD 100 <> 0 OR year MOD 400 = 0 THEN
  13.         check_leap_year = 1
  14.     ELSE
  15.         check_leap_year = 0
  16.     END IF

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Title: Re: Bplus will like this one...
Post by: Dav on December 24, 2020, 05:12:09 pm
Here's a function I think I picked it up on a VB forum somewhere.  I kept it because it was a one-line method.  Just throwing it into the mix because I have nothing else to do right now... :)

- Dav

Code: QB64: [Select]
  1. FOR t = 2020 TO 2060
  2.     IF Leapyear(t) THEN PRINT t; "is a leap year"
  4.  
  5. FUNCTION Leapyear (year)
  6.     Leapyear = (year MOD 4 = 0) XOR (year MOD 100 = 0) XOR (year MOD 400 = 0) XOR (year = 4840)
  8.  
Title: Re: Bplus will like this one...
Post by: bplus on December 24, 2020, 05:37:14 pm
At the moment I dont have time to study this but in my recollection of that week with extended timer, we started out with something from the toolbox and it worked OK going forward in time but yours truly wanted to go back in time and that's when hell week began ;-))

I wanted to go back in time to say how long it was (in seconds?) since this or that event in human history. It was for a New Years count down app that Ron77 had started. I am trying to remember if that was last year or this?

If it was for this year then there's still time to finish that up :)
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