That's not user friendly. It would be very annoying to your users and I recommend you DON'T DO THAT, especially since it's not necessary at all. Just convert what they input to upper case with the upper() function, like this:
% Set up the dialog box parameters
prompt = {'Enter temperature:','Enter the temperature scale:'};
dialogTitle = 'Enter parameters';
numberOfLines = 1;
defaultAnswers = {'100','C'};
userResponse = inputdlg(prompt, dialogTitle, numberOfLines, defaultAnswers);
% Extract out individual variables from the user response.
temperature = str2double(userResponse{1})
% Convert to upper case.
EoSI = upper(userResponse{2})
