Day and Date Functions

Liberty Basic Day and Date Routines

LB Day-of-Week Conversions

Liberty BASIC is adept at handling various date string formats. It can handle 1- or 2-digit numbers for the month and day. It will also accept fully typed month names or 3-letter abbreviations. Years can be 1, 2, 3 or 4-digit numbers. Years from 0 to 99 are assumed as 2000 to 2099.
Some examples: Jul 4, 06 -- July 04, 2006 -- 7/4/6 -- 07/04/2006

In the LB universe, day 0 was Jan 1, 1901 and dates before 1/1/1901 return negative numbers.
Be aware that negative years are incorrectly handled as positive, so LB's Date$() function can not be relied upon for any date earlier than Jan 1, 100.

• -- - harmonv

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Liberty BASIC Day of Week

This routine uses LB's built-in Date$() function.

' Return Day-of-Week for dt$
function DayofWeek$(dt$)
  day = date$(dt$) mod 7 + 7  ' +7 for dates before Jan 1, 1901
  select case (day mod 7)
    case 0: d$ = "Tuesday"
    case 1: d$ = "Wednesday"
    case 2: d$ = "Thursday"
    case 3: d$ = "Friday"
    case 4: d$ = "Saturday"
    case 5: d$ = "Sunday"
    case 6: d$ = "Monday"
  end select
  DayofWeek$ = d$
end function

Zeller's Congruence for Day of Week

This version does not use LB's internal Date$() function, so the input parameters must be numbers. This routine might be prefered by LB 3.x users since it does not use the MOD operator.

' Day of Week using Zeller's Congruence
Function ZellerDoW$(yr, mo, dy)
  m = mo - 2
  if m<1 then
    m = m + 12
    yr = yr - 1
  end if
  c = int(yr/100)
  d = yr - 100*int(yr/100)
  f = int(2.6*m - 0.2) + dy + d + int(d/4) + int(c/4) + 5*c
  f = f - 7*int(f/7)
  dow$ = "Sunday Monday Tuesday Wednesday Thursday Friday Saturday"
  ZellerDoW$ = word$(dow$, f+1)
end function

Gregorian Year, Month, Day to Day of Week

' Gregorian date to Day-of-Week #
' This returns a number between 0 and 6 (0=Sun, 1=Mon, ...)
function G2dow(yr,mo,dy)
  a = int((14-mo)/12)
  m = mo + 12*a - 2
  y = yr - a
  G2dow = (dy + y + int(y/4)-int(y/100)+int(y/400)+int(31*m/12)) mod 7
end function

Gregorian Year, Month, Day to Julian Day #

' Convert Gregorian year,month,day to Julian Day #
function G2Jd(yr,mo,dy)
  a = int((14-mo)/12)
  y = yr + 4800 - a
  m = mo + 12*a - 3
  G2Jd = dy + int((153*m+2)/5)+365*y+int(y/4)-int(y/100)+int(y/400)-32045
end function

Julian Day to Gregorian Year, Month, Day

' Julian day to Gregorian date
function Jd2G(jd, byref yr, byref mo, byref dy)
  a = jd + 32044
  b = int((4*a+3)/146097)
  c = a - int((146097*b)/4)
  d = int((4*c+3)/1461)
  e = c - int(1461*d/4)
  m = int((5*e+2)/153)
  dy = e - int((153*m+2)/5) + 1
  mo = m + 3 - 12*int(m/10)
  yr = 100*b + d - 4800 + int(m/10)
end function

Note for LB 3.x users

LB 3.x does not have the MOD operator, so you will need to provide one for some of these functions.

' LB mod function for LB 3.x users
function LBmod(a, b)
  LBmod = a - b * int(a/b)
end function

Example Usage
For the DayofWeek$() function, replace the two lines using MOD with these:

  day = LBmod( date$(dt$), 7) + 7  ' +7 for dates before Jan 1, 1901
  select case LBmod(day, 7)

Additional Information

The calculations for the Gregorian date and day routines are from Claus Tøndering's excellent Calendar FAQ page at http://www.tondering.dk/claus/calendar.html
They can be freely distributed for all non-commercial uses.

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