Loading parameters from a file and saving data

Hello,

I am working on a solver that has a large number of input parameters that I would like to load from a file. One issue I though I would have is that the size of some arrays are defined by said input. 

Eventually my program solves some distribution function (some n_x by n_v matrix) that I would like to save to a file as well.

Any ideas whats the best to do that on the Windows compiler? 

example code

program test_1

implicit none

real , parameter :: alpha=1

integer , parameter :: n_x=10

integer , parameter :: n_v=10

real,dimension(n_x,n_v) :: f

integer :: i, j

do i=1,n_x

do j =1,n_v

f(i,j)= i*j

end do

end do

end program

Here is where I want to save f to an external file for some farther analysis.

Thanks!

Best,

Erez