checkem Subroutine

       subroutine checkem
          ! validate these numbers
          do i=1,size(ccards)
             j=len(trim(ccards(i)))
             string=luhn_checksum(ccards(i)(:j-1))
             write(*,'(a,1x,a,1x,l1)')ccards(i),string,ccards(i).eq.string
          enddo

          string='123456 781-234-567'
          write(*,*)'from ',string,' got ',luhn_checksum(string), &
          & ' which should be 1234567812345670'
       end subroutine checkem