Just put it in a while loop until they get it right. Warn them like this:
message = sprintf('Error: you entered %d when you should have entered a number in the range [0,99].', theirNumber);
uiwait(warndlg(message));
In general for a try/catch you can try this:
function blahblahblah()
try
% Some code that generates an error.
catch ME
message = sprintf('Error in blahblahblah():\n%s', ME.message);
uiwait(warndlg(message));
end
