Using an array coming from a module to be used in another subroutine or main program in Fortran -

i'd glad if me this. i'm studying modules in fortran, , have question. let's module creates matrix [a(3,3)] read user's input. then, i'd use such matrix in new subroutine can operation (for sake of simplicity let's sum). code looks this:

     module matrixm                                                                                                                                                                                                          contains                                                                     subroutine matrixc                                                               integer i,j                                                                      real, dimension(3,3) ::                                                        10 i=1,3                                                                         20 j=1,3                                                                     read(*,*) a(i,j)                                                         20    continue                                                                   10    continue                                                                                                                 end subroutine matrixc                                                           end module matrixm                                                                program matrix                                                                       use matrixm                                                                  real, dimension(3,3) :: b,c                                                      integer i,j                                                                          call matrixc                                                                     b=10.0                                                                           c=a+b       write statements here...                                                                         end   

if input of is: 1 2 3 4 5 6 7 8 9 1 expect c[3,3] 11 12 13 14 15 16 17 18 19. however, result shows matrix c elemets of them equal 10.0. error have in program?, , more important, correct on what's use of module?. have similar issue on big problem i'm working on right now. thanks.

the problem have in program visible memory:

you read data in matrix a local subroutine matrixc. means, change not visible program.

the next thing is, variable a in program implicitely defined real , result, doesn't throw error (keyword: implicit none).

there 2 easy solutions:

1: put definition of matrix a in definition part of module:

module matrixm   real, dimension(3,3) ::    contains                                                              subroutine matrixc                                                               integer i,j                                                                       i=1,3                                                                        j=1,3                                                                       read(*,*) a(i,j)                 end                                                       end                                                                      end subroutine matrixc                                                     end module matrixm 

2: use a parameter subroutine , define in main program:

module matrixm   contains                                                              subroutine matrixc(a)                                                 integer i,j       real, dimension(3,3) ::        i=1,3                                                                        j=1,3                                                                       read(*,*) a(i,j)                 end                                                       end                                                                      end subroutine matrixc                                                     end module matrixm  program matrix                                                           use matrixm    implicit none                                                             real, dimension(3,3) :: a,b,c                                                 integer i,j    call matrixc(a)                                                             b=10.0                                                                   c=a+b    write statements here...                                                                   end program