get_choice v2.3

% 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.