...
fullFileName = fullfile(theFiles(k).folder, baseFileName);
fprintf(1, 'Now reading %s\n', fullFileName);
plot(fullFileName(:,4),fullFileName(:,5));
...
You created a fully-qualified file name, but you never used it to read the file.
Your plot() command uses the filenames as variables for x,y but those are the names of the files, the name doesn't contain the data in the file; you have to read it some way.
The code link you used as a pattern was looking at .png files so it used
...
% such as reading it in as an image array with imread()
imageArray = imread(fullFileName);
imshow(imageArray); % Display image.
...
to read and display the image in the file. Your simple text file format with no header line will be easy with
...
fullFileName = fullfile(theFiles(k).folder, baseFileName);
disp(['Now reading ', fullFileName])
data=readmatrix(fullFileName);
plot(data(:,4),data(:,5));
...
As written, each loop will replace the preceding line with the next; you're missing a key element to plot all on one graph--"hold". Read documenation for it to get the bigger picture...
You could also streamline the sample code a little; it was written to make every step obvious which isn't all bad...
myFolder = 'Users\adminstrator\Desktop\Curves';
d=dir(fullfile(myFolder, '*.txt'));
figure, hold on
for k = 1:numel(d)
data=readmatrix(fullfile(d(k).folder,d(k).name);
plot(data(:,4),data(:,5));
end
