function file_name_new = file_name_inc ( file_name )

% FILE_NAME_INC generates the next filename in a series.
%
%  Discussion:
%
%    It is assumed that the digits in the name, whether scattered or
%    connected, represent a number that is to be increased by 1 on
%    each call.  If this number is all 9's on input, the output number
%    is all 0's.  Non-numeric letters of the name are unaffected, and
%    if the name contains no digits, then nothing is done.
%
%  Examples:
%
%      Input          Output
%      -----          ------
%      a7to11.txt     a7to12.txt
%      a7to99.txt     a8to00.txt
%      a9to99.txt     a0to00.txt
%      cat.txt        cat.txt
%
%  Modified:
%
%    15 August 2005
%
%  Author:
%
%    John Burkardt
%
%  Parameters:
%
%    Input, character FILE_NAME(*), the string to be incremented.
%
%    Output, character FILE_NAME_NEW(*), the incremented string.
%
  lens = length ( file_name );

  file_name_new = file_name;

  for i = lens : -1 : 1

    c = file_name_new(i);

    if ( '0' <= c & c <= '8' )

      c = c + 1;
      
      file_name_new(i) = c;

      return

    elseif ( c == '9' )

      c = '0';
      
      file_name_new(i) = c;

    end

  end