Writing slider output to data file

Hi everyone. I have a little MATLAB script that involves a slider uicontrol, and I want the value output of that to be recorded in the datafile. However, I can't seem to get it to work, it keeps giving me error messages that I can't figure out how to fix. Here is my script:

function semjudge

SubNum = input('Subject Number: ','s');

files = dir(fullfile('pictures','*.png'));
nFiles = numel(files);
combos = nchoosek(1:nFiles, 2);
index = combos(randperm(size(combos, 1)), :);
picture1 = files(index(1)).name;
picture2 = files(index(2)).name;
image1 = fullfile('pictures',picture1);
image2 = fullfile('pictures',picture2);
subplot(1,2,1); imshow(image1); title(picture1);
subplot(1,2,2); imshow(image2); title(picture2);

uicontrol('Style', 'text',...
        'Position', [200 45 200 20],...
        'String','How related are these pictures?');
uicontrol('Style', 'text',...
        'Position', [50 45 100 20],...
        'String','Unrelated');
uicontrol('Style', 'text',...
        'Position', [450 45 100 20],...
        'String','Closely related');
uicontrol('Style','pushbutton','String','Next Trial',...
        'Position', [250 350 100 20],...
        'Callback','clf; semjudge()');

h = uicontrol(gcf,...
   'Style','slider',...
   'Min' ,0,'Max',50, ...
   'Position',[100 20 400 20], ...
   'Value', 25,...
   'SliderStep',[0.02 0.1], ...
   'BackgroundColor',[0.8,0.8,0.8]);

set(gcf, 'WindowButtonMotionFcn', @cb);

lastVal = get(h, 'Value'); 

 function cb(s,e)
      fid = fopen(strcat('data','_',SubNum,'.txt'),'a');
      if get(h, 'Value') ~= lastVal 
      lastVal = get(h, 'Value'); 
      fprintf(fid, '%s\t%s\t%f\n', picture1, picture2, lastVal);
      end
 end

fclose(fid);

end

Can anybody help me fix this? I really don't understand why this doesn't work. It just keeps telling me that "fid" isn't defined, or similar error messages.

Answer 1

[Oleg Komarov]

Your fid exists within the workspace of the function cb. You have to close it inside the function or you should return the fid as an output.