Guide

!********************************************
!* Compute number of days between two dates *
!* —————————————- *
!* Ref.: “Mathématiques par l’informatique *
!* individuelle (1) par H. Lehning *
!* et D. Jakubowicz, Masson, Paris, *
!* 1982″ [BIBLI 06]. *
!* *
!* F90 version by J-P Moreau, Paris. *
!********************************************

!*****************************************************************************
! Note: The two dates must be between 01/01/1901
! and 12/31/2099 to avoid treatment of special
! “secular” years, such as 1800, 1900, 2100…
! (2000, a multiple of 400, is a normal year!)!
!
! The first date is M, D, Y
! N, number of days between first date and fictitious
! starting date 01/00/1901, is given by formula:
!
! N = INT(365,25*(Y-1901)+A(M)+D)
!
! where A(M) is given by table below:
!
! M 1 2 3 4 5 6 7 8 9 10 11 12
! A(M) 0 31 59,25 90,25 120,25 151,25 181,25 212,25 243,25 273,25 304,25 334,25
!
! First N is saved in R.
!
! The second date is again M, D, Y
! N is again computed with same formula.
!
! Final result is N - R.
!*******************************************************************************
PROGRAM NDAYS

REAL*4 A(12)
REAL*4 N ! number of days
INTEGER R ! number of days

A(1) = 0; A(2) = 31; A(3) = 59.25; A(4) = 90.25; A(5) = 120.25; A(6) = 151.25
A(7) = 181.25; A(8) = 212.25; A(9) = 243.25; A(10) = 273.25; A(11) = 304.25
A(12) = 334.25

print *,”
print *,’ Compute number of days between two dates’
print *,’ (from 01/01/1901 to 12/31/2099)’
print *,”
print *,’ Enter first date (M D Y): ‘
call Calcul(A,N)
R = N
print *,’ Enter second date (M D Y): ‘
call Calcul(A,N)
R = N - R
print *,”
print *,’ Number of days: ‘,R
print *,”; print *,”
stop
end

Subroutine Calcul(A,N)
integer M,D,Y !month,day,year
REAL*4 N,A(12)
read *, M, D, Y
N = 365.25 * (Y - 1901) + A(M) + D
N = int(N)
return
end

! end of file ndays.f90