Several options depending on what you want/need...
a) if you're processing all the *.txt files in a subdirectory, there's no reason to have to select each manually -- use something like
d=dir('*.txt');
for ix=1:length(d)
fn=d(i).name
... do processing here, save results w/ dynamic output file name...
...
end
b) if you aren't doing all but know which ones, use uigetfile() but use the multipleselection optional input option --
fn=uigetfile('*.txt','Select the INPUT DATA FILE(s)','MultiSelect','on');
Then use a loop like above except the filenames are in the cell string array instead of a structure
Or,
c) if you really do need to select manually each time, just wrap your code in a while() loop and continue as long as there is a valid selection each time through...
flg=true; % set the logic variable to start the loop
while flg
fn=uigetfile('*.txt','Select the INPUT DATA FILE(s)','MultiSelect','on');
if isequal(filename,0), flg=0; break; end % no file selected; quit
% otherwise process as above here
...
end
