get_choice(prompt,responses)

function [choice,extra]= get_choice(prompt,responses)
%
% Version 2.3
%
% Written by Phillip M. Feldman  7 May, 2008
%
% get_choice displays a prompt, reads a response (string) from standard
% input, trims trailing blanks, converts to lower case, and compares the
% result against strings in the "responses" cell array.  If the response
% matches an entry in the cell array, the index of the first matching
% entry is returned.  If the user types 'quit' or 'exit', the program is
% stopped.  If the user input does not match any of these conditions, an
% error message is generated and the prompt is displayed again.
%
% Notes:
%
% 1. To implement a default response, the calling program must include a
% null string ('') as one of the entries in the responses cell array.
%
% 2. To implement multiple versions of any given response, the calling
% program should use nested cell arrays (see the example below).
%
% Example:
%
% choice= get_choice('Do you want to continue? ', ...
%   {{'n','no'},{'y','yes'},'maybe'});
%
% The above call returns 1 if the user enters 'n' or 'no', 2 if the user
% enters 'y' or 'yes', and 3 if the user enters 'maybe'.


% Revision History

% Version 2.3, 7 May, 2008

% Modified code to perform case-insensitive string comparisons rather than
% converting input to lower case.  The main reason for this change is that
% the 'extra' string may contain the name of a workspace variable, in which
% case upper/lower case must be preserved.

% Version 2.2, 5 Feb, 2008

% The function was modified to allow for a second argument that returns
% any additional tokens that follow the initial input token.  For backwards
% compatibility, this second argument is optional.

% Version 2.1, 12-11-2007

% The function was modified to test whether responses is a cell array of
% strings.  If not, it is assumed to contain a single string, in which
% case the comparison against the input text must be performed
% differently to ensure that the entire string is compared against the
% user input.

% Version 2.0, 4-4-2006

% To allow a variable number of strings in each set of responses, the
% function was modified to expect the allowed responses to be specified
% via a cell array of strings rather than a matrix of strings.  The
% function was also modified to strip trailing blanks from user input.

while (1)
   text= deblank(input(prompt, 's'));

   % Check for the presence of an extra token or tokens.  We can do this
   % by searching for a blank.  Because we have removed trailing blanks
   % above, any blank must be followed by at least one non-blank character.

   i= find(text==' ', 1, 'first');
   if (isempty(i))
      if (nargout>=2), extra= []; end
   else
      if (nargout>=2), extra= text(i+1:end); end
      text= text(1:i-1);
   end

   for i= 1 : length(responses)

      if (iscellstr(responses{i}))

         % responses{i} is a cell array of strings. test for a match to
         % any of the strings:

         if (any(strcmpi(text,responses{i}(:))))
            choice= i;
            return;
         end

      else

         % responses{i} is not a cell array of strings.  test for exact
         % string match:

         if (strcmpi(text,responses{i}))
            choice= i;
            return;
         end

      end

   end

   if (strcmpi(text,'quit') | strcmp(text,'exit'))
      error('User-requested stop.');
   end

   fprintf ('Enter a valid input or type quit to stop the program.\n');

end