;********************************************************************************
;This subroutine will increment forward (flag=1) or backward (flag=-1) the day
;month and year.  Inputs are long words
;*******************************************************************************
pro dtgincre_day, day, mnum, yy, flag


;**********************************************************
;Check if the year is a leap year
;**********************************************************
leap_flag=0  ;not a leap year
check4=(yy) mod 4
check100=(yy) mod 100
check400=(yy)mod 400
if (  (check4 eq 0 and check100 ne 0) or (check400 eq 0) ) then leap_flag=1  ;leap yea

if (flag gt 0) then begin

	day=day+1
	hr=0
	if (day eq 30 and mnum eq 2 and leap_flag eq 1) then begin
		mnum=mnum+1
		day=1
	endif
	if (day eq 29 and mnum eq 2 and leap_flag eq 0) then begin
		mnum=mnum+1
		day=1
	endif
	if (day ge 31) then begin
		if (mnum eq 9 or mnum eq 4 or mnum eq 6 or mnum eq 11) then begin
			mnum=mnum+1
			day=1
		endif else begin

			if (day eq 32) then begin
				mnum=mnum+1
				day=1
			 	if (mnum eq 13) then begin
			 		mnum=1
			 		yy=yy+1
			 	endif
			 endif
		endelse
	endif


endif else begin

	day=day-1
	if (day eq 0) then begin
		mnum=mnum-1
		if (mnum eq 0) then begin
			mnum=12
			yy=yy-1
		endif
		if (mnum eq 2 and leap_flag eq 1) then day=29
		if (mnum eq 2 and leap_flag eq 0) then day=28
		if (mnum eq 9 or mnum eq 4 or mnum eq 6 or mnum eq 11) then begin
			day=30
		endif else begin
			if (mnum ne 2) then day=31
		endelse

	endif


endelse

end