; Yesterday.kix,  Version 1.00
; Display today's and yesterday's date in two formats
; Written by Rob van der Woude
; http://www.robvanderwoude.com

; Today's date in YYYYMMDD format
$SortDate = ( 10000 * @YEAR ) + ( 100 * @MONTHNO ) + @MDAYNO

; Calculate yesterday's date
$YesterD = @MDAYNO - 1
$YesterM = @MONTHNO
$YesterY = @YEAR

; It gets tricky when today is the first day of the month
IF $YesterD = 0
	GOSUB RollMonth
ENDIF

; Yesterday's date in YYYYMMDD format
$SortYest = ( 10000 * $YesterY ) + ( 100 * $YesterM ) + $YesterD

; Display the results
? "Format:     YYYYMMDD  (DD/MM/YYYY)"
? "=================================="
? "Today:      $SortDate  (@MDAYNO/@MONTHNO/@YEAR)"
? "Yesterday:  $SortYest  ($YesterD/$YesterM/$YesterY)"
?

; Done
EXIT


; * * * * * * * *  Subroutines  * * * * * * * *


; Subroutine to get yesterday's date if today is the first day of the month
:RollMonth
$YesterM = $YesterM - 1
SELECT
	CASE $YesterM = 0 ; Today is January 1st
		$YesterD = 31
		$YesterM = 12
		$YesterY = @YEAR - 1
	CASE $YesterM = 1 ; Today is February 1st
		$YesterD = 30
	CASE $YesterM = 2 ; Today is March 1st
		$YesterD = 28
		GOSUB LeapYear
	CASE $YesterM = 3 ; Today is April 1st
		$YesterD = 31
	CASE $YesterM = 4 ; Today is May 1st
		$YesterD = 30
	CASE $YesterM = 5 ; Today is June 1st
		$YesterD = 31
	CASE $YesterM = 6 ; Today is July 1st
		SET YesterD=30
	CASE $YesterM = 7 ; Today is August 1st
		$YesterD = 31
	CASE $YesterM = 8 ; Today is September 1st
		$YesterD = 31
	CASE $YesterM = 9 ; Today is October 1st
		$YesterD = 30
	CASE $YesterM = 10 ; Today is November 1st
		$YesterD = 31
	CASE $YesterM = 11 ; Today is December 1st
		$YesterD = 30
ENDSELECT
RETURN


; Subroutine to calculate if this year is a leap year
; (I am not sure if the century calculations are right)
:LeapYear
; If the year divisable by 4 then it is a leap year . . .
$LeapYear = ( @YEAR / 4 ) * 4
IF $LeapYear = @YEAR
	$YesterD = 29
ENDIF
; . . . unless it is also divisible by 100 . . .
$LeapYear = ( @YEAR / 100 ) * 100
IF $LeapYear = @YEAR
	$YesterD = 28
ENDIF
; . . . but when it is divisible by 400 it is a leap year again (?)
$LeapYear = ( @YEAR / 400 ) * 400
IF $LeapYear = @YEAR
	$YesterD = 29
ENDIF
RETURN