program read_file
      implicit none
      integer     N_LINES, file_unit, line
      parameter ( N_LINES = 20, file_unit = 10 )
      integer          i_vec(N_LINES)
      double precision d_vec(N_LINES)
    
* Open the file named infile
      open(unit = file_unit, file = 'infile', form = 'formatted', 
     +     access = 'sequential', status = 'old')
    
* Read the data
      do line = 1, N_LINES
        read(file_unit, *) i_vec(line), d_vec(line)
      end do
    
* Close the file
      close(file_unit, status = 'keep')
    
* Print what we just read
      do line = 1, N_LINES
        print*, i_vec(line), d_vec(line)
      end do
    
*------------------------------------------------ 
* If we don't know the number of lines in he file
* we can do like this. Note that i_vec and d_vec
* MUST have room for the elements.
    
      open(unit = file_unit, file = 'infile', form = 'formatted', 
     +     access = 'sequential', status = 'old')
    
      line = 1  ! counts the number of lines
    
* end = 100 means: jump to the line with label 100 at end of file
      do
        read(file_unit, *, end = 100) i_vec(line), d_vec(line)
        line = line + 1
      end do
    
100   line = line - 1 ! we did not read anything the last time
    
      print*, '# of lines = ', line
      close(file_unit, status = 'keep')
*
* Start computing ...
*
      end