unknown wrong in a fortran array code

Question

I checked this code many times and could not figure out how to correct it.

program main
implicit none

real, parameter :: dx=1
real, parameter :: dy=1

real :: a1, a2, a3, a4, a5
a1=dy/dx
a2=dx/dy
a3=-2*(dy/dx+dx/dy)
a4=dx/dy
a5=dy/dx

REAL, DIMENSION(5,1):: a
DATA a/a1,a2,a3,a4,a5/

!write (*,*) a(1),a(2)
pause
endprogram

thank you very much and the error:
error #6236:A specification statement cannot appear in the executable section. error #6404: This name does not have a type, and must have an explicit type. [A] error #6211: A symbol must be a defined parameter in this context.

Vladimir F Героям слава · Accepted Answer · 2015-11-07 16:51:14Z

2

You are mixing specification (data declaration) statements and executable statements. The declaration statements must go first and the executable statements can only follow after them inside each compilation unit or block.

Also, entity used for initialization in the DATA statement must be a constant expression.

One way to fix your code is:

program main
  implicit none

  real, parameter :: dx=1
  real, parameter :: dy=1

  real, parameter :: a1=dy/dx
  real, parameter :: a2=dx/dy
  real, parameter :: a3=-2*(dy/dx+dx/dy)
  real, parameter :: a4=dx/dy
  real, parameter :: a5=dy/dx

  REAL, DIMENSION(5,1):: a
  DATA a/a1,a2,a3,a4,a5/

  !write (*,*) a(1),a(2)

end program

Don't use the PAUSE statement. It is deleted from modern Fortran and it is not clear (portably) what should it actually do even in the older versions.

You can also initialize the array using an array constructor. You don't need constant expressions in that case:

program main
  implicit none

  real, parameter :: dx=1
  real, parameter :: dy=1
  REAL, DIMENSION(5,1) :: a

  a = reshape([dy/dx, dx/dy, -2*(dy/dx+dx/dy), dx/dy, dy/dx], [5,1])
end program

edited Nov 7, 2015 at 16:51

answered Nov 7, 2015 at 16:43

Vladimir F Героям слава

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2 Comments

gugabrielle Over a year ago

thank you so much. it was my first time to write fortran code and struggled a lot for the format which is quite different from c++

Vladimir F Героям слава Over a year ago

Yes, in C and C++ you can define variables even after some executale statements. Not so in Fortran.

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