program main

!*****************************************************************************80
!
!! fair_dice_simulation() simulates N throws of two fair dice.
!
!  Usage:
!
!    fair_dice n
!
!    where 
!
!    * n is the number of times the dice should be thrown.
!
!  Licensing:
!
!    This code is distributed under the MIT license.
!
!  Modified:
!
!    06 September 2012
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Command line, integer N, the number of times the dice 
!    are thrown.
!
  implicit none

  integer arg_num
  character ( len = 255 ) command_filename
  integer command_unit
  character ( len = 255 ) data_filename
  integer data_unit
  integer die1
  integer die2
  integer i
  integer i4_uniform
  integer iarg
  integer ierror
  integer last
  integer n
  integer seed
  integer score
  integer score_count(12)
  character ( len = 80 ) string

  call timestamp ( )
  write ( *, '(a)' ) ''
  write ( *, '(a)' ) 'fair_dice_simulation():'
  write ( *, '(a)' ) '  FORTRAN90 version'
  write ( *, '(a)' ) '  Simulate N throws of a pair of fair dice.'
!
!  Get the number of command line arguments.
!
  arg_num = iargc ( )
!
!  Get the quadrature file root name:
!
  if ( 1 <= arg_num ) then

    iarg = 1
    call getarg ( iarg, string )
    call s_to_i4 ( string, n, ierror, last )
  else

    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) '  Enter N, the number of times the dice are thrown: '

    read ( *, * ) n

  end if
!
!  Initialize the random number generator.
!
  call get_seed ( seed )
!
!  For convenience, include slots for 0 and 1, even though they never occur.
!
  score_count(1:12) = 0
!
!  Roll N times.
!
  do i = 1, n
    die1 = i4_uniform ( 1, 6, seed )
    die2 = i4_uniform ( 1, 6, seed )
    score = die1 + die2
    score_count(score) = score_count(score) + 1
  end do
!
!  Write the data file.
!
  data_filename = 'fair_dice_data.txt'
  call get_unit ( data_unit )
  open ( unit = data_unit, file = data_filename, status = 'replace' )

  do score = 2, 12
    write ( data_unit, '(2x,i2,2x,i6)' ) score, score_count(score)
  end do

  close ( unit = data_unit )
  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  Created data file "' // trim ( data_filename ) // '".'
!
!  Write the command file.
!
  command_filename = 'fair_dice_commands.txt'

  call get_unit ( command_unit )
  open ( unit = command_unit, file = command_filename, status = 'replace' )

  write ( command_unit, '(a)' ) '# ' // trim ( command_filename )
  write ( command_unit, '(a)' ) '#'
  write ( command_unit, '(a)' ) '# Usage:'
  write ( command_unit, '(a)' ) '#  gnuplot << ' // trim ( command_filename )
  write ( command_unit, '(a)' ) '#'
  write ( command_unit, '(a)' ) 'set term png'
  write ( command_unit, '(a)' ) 'set output "fair_dice.png"'
  write ( command_unit, '(a)' ) 'set xlabel "<---Score--->"'
  write ( command_unit, '(a)' ) 'set ylabel "<---Frequency--->"'
  write ( command_unit, '(a)' ) 'set title "Score frequency for a pair of fair dice"'
  write ( command_unit, '(a)' ) 'set grid'
  write ( command_unit, '(a)' ) 'set style fill solid'
  write ( command_unit, '(a)' ) 'set yrange [0:*]'
  write ( command_unit, '(a)' ) 'set timestamp'
  write ( command_unit, '(a)' ) 'unset key'
  write ( command_unit, '(a,i4,a)' ) &
    'plot "fair_dice_data.txt" using 1:2:(0.90):xtic(3) with boxes'
  write ( command_unit, '(a)' ) 'quit'

  close ( unit = command_unit )

  write ( *, '(a)' ) '  Created command file "' // trim ( command_filename ) // '".'
!
!  Terminate.
!
  write ( *, '(a)' ) ''
  write ( *, '(a)' ) 'FAIR_DICE_SIMULATION:'
  write ( *, '(a)' ) '  Normal end of execution.'
  write ( *, '(a)' ) ''
  call timestamp ( )

  return
end
subroutine get_seed ( seed )

!*****************************************************************************80
!
!! GET_SEED returns a seed for the random number generator.
!
!  Discussion:
!
!    The seed depends on the current time, and ought to be (slightly)
!    different every millisecond.  Once the seed is obtained, a random
!    number generator should be called a few times to further process
!    the seed.
!
!  Licensing:
!
!    This code is distributed under the MIT license. 
!
!  Modified:
!
!    02 August 2004
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Output, integer SEED, a pseudorandom seed value.
!
  implicit none

  integer, parameter :: rk = kind ( 1.0D+00 )

  integer, parameter :: i4_huge = 2147483647
  integer seed
  real ( kind = rk ) temp
  character ( len = 10 ) time
  character ( len = 8 ) today
  integer values(8)
  character ( len = 5 ) zone

  call date_and_time ( today, time, zone, values )

  temp = 0.0D+00

  temp = temp + real ( values(2) - 1, kind = rk ) /  11.0D+00
  temp = temp + real ( values(3) - 1, kind = rk ) /  30.0D+00
  temp = temp + real ( values(5),     kind = rk ) /  23.0D+00
  temp = temp + real ( values(6),     kind = rk ) /  59.0D+00
  temp = temp + real ( values(7),     kind = rk ) /  59.0D+00
  temp = temp + real ( values(8),     kind = rk ) / 999.0D+00
  temp = temp                                    /   6.0D+00

  do while ( temp <= 0.0D+00 )
    temp = temp + 1.0D+00
  end do

  do while ( 1.0D+00 < temp )
    temp = temp - 1.0D+00
  end do

  seed = int ( real ( i4_huge, kind = rk ) * temp )
!
!  Never use a seed of 0 or maximum integer.
!
  if ( seed == 0 ) then
    seed = 1
  end if

  if ( seed == i4_huge ) then
    seed = seed - 1
  end if

  return
end
subroutine get_unit ( iunit )

!*****************************************************************************80
!
!! GET_UNIT returns a free FORTRAN unit number.
!
!  Discussion:
!
!    A "free" FORTRAN unit number is a value between 1 and 99 which
!    is not currently associated with an I/O device.  A free FORTRAN unit
!    number is needed in order to open a file with the OPEN command.
!
!    If IUNIT = 0, then no free FORTRAN unit could be found, although
!    all 99 units were checked (except for units 5, 6 and 9, which
!    are commonly reserved for console I/O).
!
!    Otherwise, IUNIT is a value between 1 and 99, representing a
!    free FORTRAN unit.  Note that GET_UNIT assumes that units 5 and 6
!    are special, and will never return those values.
!
!  Licensing:
!
!    This code is distributed under the MIT license. 
!
!  Modified:
!
!    26 October 2008
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Output, integer IUNIT, the free unit number.
!
  implicit none

  integer i
  integer ios
  integer iunit
  logical lopen
 
  iunit = 0
 
  do i = 1, 99
 
    if ( i /= 5 .and. i /= 6 .and. i /= 9 ) then

      inquire ( unit = i, opened = lopen, iostat = ios )
 
      if ( ios == 0 ) then
        if ( .not. lopen ) then
          iunit = i
          return
        end if
      end if

    end if
 
  end do

  return
end
function i4_uniform ( a, b, seed )

!*****************************************************************************80
!
!! I4_UNIFORM returns a scaled pseudorandom I4.
!
!  Discussion:
!
!    An I4 is an integer value.
!
!    The pseudorandom number will be scaled to be uniformly distributed
!    between A and B.
!
!  Licensing:
!
!    This code is distributed under the MIT license.
!
!  Modified:
!
!    12 November 2006
!
!  Author:
!
!    John Burkardt
!
!  Reference:
!
!    Paul Bratley, Bennett Fox, Linus Schrage,
!    A Guide to Simulation,
!    Springer Verlag, pages 201-202, 1983.
!
!    Pierre L'Ecuyer,
!    Random Number Generation,
!    in Handbook of Simulation,
!    edited by Jerry Banks,
!    Wiley Interscience, page 95, 1998.
!
!    Bennett Fox,
!    Algorithm 647:
!    Implementation and Relative Efficiency of Quasirandom
!    Sequence Generators,
!    ACM Transactions on Mathematical Software,
!    Volume 12, Number 4, pages 362-376, 1986.
!
!    Peter Lewis, Allen Goodman, James Miller
!    A Pseudo-Random Number Generator for the System/360,
!    IBM Systems Journal,
!    Volume 8, pages 136-143, 1969.
!
!  Parameters:
!
!    Input, integer A, B, the limits of the interval.
!
!    Input/output, integer SEED, the "seed" value, which
!    should NOT be 0.  On output, SEED has been updated.
!
!    Output, integer I4_UNIFORM, a number between A and B.
!
  implicit none

  integer, parameter :: rk = kind ( 1.0D+00 )

  integer a
  integer b
  integer, parameter :: i4_huge = 2147483647
  integer i4_uniform
  integer k
  real ( kind = rk ) r
  integer seed
  integer value

  if ( seed == 0 ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) 'I4_UNIFORM - Fatal error!'
    write ( *, '(a)' ) '  Input value of SEED = 0.'
    stop
  end if

  k = seed / 127773

  seed = 16807 * ( seed - k * 127773 ) - k * 2836

  if ( seed < 0 ) then
    seed = seed + i4_huge
  end if

  r = real ( seed, kind = rk ) * 4.656612875D-10
!
!  Scale R to lie between A-0.5 and B+0.5.
!
  r = ( 1.0D+00 - r ) * ( real ( min ( a, b ), kind = rk ) - 0.5D+00 ) &
    +             r   * ( real ( max ( a, b ), kind = rk ) + 0.5D+00 )
!
!  Use rounding to convert R to an integer between A and B.
!
  value = nint ( r )

  value = max ( value, min ( a, b ) )
  value = min ( value, max ( a, b ) )

  i4_uniform = value

  return
end
subroutine s_to_i4 ( s, ival, ierror, length )

!*****************************************************************************80
!
!! S_TO_I4 reads an I4 from a string.
!
!  Licensing:
!
!    This code is distributed under the MIT license. 
!
!  Modified:
!
!    28 June 2000
!
!  Author:
!
!    John Burkardt
!
!  Parameters:
!
!    Input, character ( len = * ) S, a string to be examined.
!
!    Output, integer IVAL, the integer value read from the string.
!    If the string is blank, then IVAL will be returned 0.
!
!    Output, integer IERROR, an error flag.
!    0, no error.
!    1, an error occurred.
!
!    Output, integer LENGTH, the number of characters of S 
!    used to make IVAL.
!
  implicit none

  character c
  integer i
  integer ierror
  integer isgn
  integer istate
  integer ival
  integer length
  character ( len = * ) s

  ierror = 0
  istate = 0
  isgn = 1
  ival = 0

  do i = 1, len_trim ( s )

    c = s(i:i)
!
!  Haven't read anything.
!
    if ( istate == 0 ) then

      if ( c == ' ' ) then

      else if ( c == '-' ) then
        istate = 1
        isgn = -1
      else if ( c == '+' ) then
        istate = 1
        isgn = + 1
      else if ( lle ( '0', c ) .and. lle ( c, '9' ) ) then
        istate = 2
        ival = ichar ( c ) - ichar ( '0' )
      else
        ierror = 1
        return
      end if
!
!  Have read the sign, expecting digits.
!
    else if ( istate == 1 ) then

      if ( c == ' ' ) then

      else if ( lle ( '0', c ) .and. lle ( c, '9' ) ) then
        istate = 2
        ival = ichar ( c ) - ichar ( '0' )
      else
        ierror = 1
        return
      end if
!
!  Have read at least one digit, expecting more.
!
    else if ( istate == 2 ) then

      if ( lle ( '0', c ) .and. lle ( c, '9' ) ) then
        ival = 10 * ival + ichar ( c ) - ichar ( '0' )
      else
        ival = isgn * ival
        length = i - 1
        return
      end if

    end if

  end do
!
!  If we read all the characters in the string, see if we're OK.
!
  if ( istate == 2 ) then
    ival = isgn * ival
    length = len_trim ( s )
  else
    ierror = 1
    length = 0
  end if

  return
end
subroutine timestamp ( )

!*****************************************************************************80
!
!! TIMESTAMP prints the current YMDHMS date as a time stamp.
!
!  Example:
!
!    31 May 2001   9:45:54.872 AM
!
!  Licensing:
!
!    This code is distributed under the MIT license.
!
!  Modified:
!
!    18 May 2013
!
!  Author:
!
!    John Burkardt
!
  implicit none

  character ( len = 8 ) ampm
  integer d
  integer h
  integer m
  integer mm
  character ( len = 9 ), parameter, dimension(12) :: month = (/ &
    'January  ', 'February ', 'March    ', 'April    ', &
    'May      ', 'June     ', 'July     ', 'August   ', &
    'September', 'October  ', 'November ', 'December ' /)
  integer n
  integer s
  integer values(8)
  integer y

  call date_and_time ( values = values )

  y = values(1)
  m = values(2)
  d = values(3)
  h = values(5)
  n = values(6)
  s = values(7)
  mm = values(8)

  if ( h < 12 ) then
    ampm = 'AM'
  else if ( h == 12 ) then
    if ( n == 0 .and. s == 0 ) then
      ampm = 'Noon'
    else
      ampm = 'PM'
    end if
  else
    h = h - 12
    if ( h < 12 ) then
      ampm = 'PM'
    else if ( h == 12 ) then
      if ( n == 0 .and. s == 0 ) then
        ampm = 'Midnight'
      else
        ampm = 'AM'
      end if
    end if
  end if

  write ( *, '(i2,1x,a,1x,i4,2x,i2,a1,i2.2,a1,i2.2,a1,i3.3,1x,a)' ) &
    d, trim ( month(m) ), y, h, ':', n, ':', s, '.', mm, trim ( ampm )

  return
end