Writing multiple output files in Fortran

Question

Dear All, I am writing a code that writes the out put in multiple files named as 1.dat, 2.dat, ..... Here is my code but it gives some unusual output. May you tell me what is wrong in my code please? Basically I could not get the correct syntax to open multiple files, write on them and close before the next file is opened. Thank you. My Code:

implicit double precision (a-h,o-z),integer(i-n)
dimension b(3300,78805),bb(78805)
character*70,fn 
character*80,fnw 
nf = 3600       ! NUMBER OF FILES
nj = 360        ! Number of rows in file.
do j = 1, nj
    bb(j)  = 0.0
end do
c-------!Body program-----------------------------------------------
iout = 0    ! Output Files upto "ns" no.
DO i= 1,nf  ! LOOP FOR THE NUMBER OF FILES
    if(mod(i,180).eq.0.0) then
        open(unit = iout, file = 'formatted')
        x = 0.0
        do j = 1, nj
            bb(j) = sin(x)
            write(iout,11) int(x),bb(j)
            x = x + 1.0
        end do
        close(iout)
        iout = iout + 1
    end if
END DO
11  format(i0,'.dat')   
END

Answer 1

So there are a few things not immediately clear about your code, but I think here the most relevant bits are that you want to specify the filename with file = in the open statement, not the formatting, and looping over units with iout is problematic because you'll eventually hit system-defined units for stdin and stdout. Also, with that format line it looks like you're getting ready to create the filename, but you never actually use it.

I'm not sure where you're; going with the mod test, etc, but below is a stripped down version of above which just creates the files ina loop:

program manyfiles
    implicit none
    character(len=70) :: fn
    integer, parameter :: numfiles=40
    integer, parameter :: outunit=44

    integer :: filenum, j

    do filenum=1,numfiles
        ! build filename -- i.dat
        write(fn,fmt='(i0,a)') filenum, '.dat'

        ! open it with a fixed unit number
        open(unit=outunit,file=fn, form='formatted')

        ! write something
        write(outunit, *) filenum

        ! close it 
        close(outunit)
    enddo
end program manyfiles