I would like to pass the array dimension as a dummy variable to a subroutine. The array itself is on a common block. Here is the code:
PROGRAM test
integer i, nn
integer PARAMETER(Nt=10)
real x(Nt), y(nt), z(Nt)
Common /Bdat/ z
nn=Nt
do i=1,Nt
x(i)=i+1
z(i)=i-1
enddo
call estimate(x,y,nn)
print*, y
return
end
subroutine estimate(x,y,jj)
integer i,jj
real x(jj), y(jj), zq(jj)
COMMON /Bdat/ zq
do i=1, jj
y(i)=x(i)+zq(i)
enddo
return
end
this is the error I get from the subroutine:
real x(jj), y(jj), zq(jj)
1
Error: Variable 'jj' at (1) in this context must be constant
I would really appreciate it if anybody could solve the issue.
You have a scope problem. Read: Scope in Fortran. That is, your subroutine estimate needs access to the variable Nt which you need to pass as an additional argument, or you can move the entire subroutine inside your program using the contains statement. This will allow your program to run successfully, but I highly encourage you to abstain from using common blocks. If you cannot avoid them due to legacy codes see: Improve your FORTRAN 77 programs using some Fortran 90 features
Try using modules instead:
module bdat
implicit none
private
public :: NT, z
integer, parameter :: NT = 10
real :: z(NT)
end module bdat
module my_sub
use bdat, only: &
zq => z ! You're free to rename the variable
implicit none
private
public :: estimate
contains
subroutine estimate(x,y)
! calling arguments
real, intent (in) :: x(:)
real, intent (out) :: y(:)
! local variables
integer :: i, jj
jj = size(x)
do i=1, jj
y(i)=x(i)+zq(i)
end do
end subroutine estimate
end module my_sub
program test
use bdat, only: &
NT, z
use my_sub, only: &
estimate
implicit none
integer :: i
real :: x(NT), y(NT)
do i=1,NT
x(i)=i+1
z(i)=i-1
end do
call estimate(x,y)
print *, y
end program test