Question

I am working through the Fortran tutorial at http://en.wikibooks.org/wiki/Fortran/Fortran_simple_input_and_output. In the following program, what does unit=out_unit do?

program xproduct
  implicit none
  integer            :: i,j
  integer, parameter :: out_unit=20

  print*,"enter two integers"
  read (*,*) i,j

  open (unit=out_unit,file="results.txt",action="write",status="replace")
  write (out_unit,*) "The product of",i," and",j
  write (out_unit,*) "is",i*j

  close (out_unit)
end program xproduct

When I run this program, the text file results.txt contains the following text:

 The product of           2  and           3
 is           6

Answer 1

It specifies the “terminal” to write to. The number contained in out_unit represents the file you opened with the open statement. If you hadn’t used the open statement and specified the file, output would have been to fort.20

Some terminal numbers have specific meanings. For example, 6 is (usually) stdout, and 5 is (usually) stdin.