I am attempting to only allow users to respond using the 'j' key or the 'k' key. For some reason MATLAB doesn't allow users to respond using the 'k' key. Instead it displays the error that "'k' is an undefined function or variable"

I have the following code; it allows users to respond using the 'j' key but unfortunately not the 'k' key.

f=figure(1);
for i=1:21
    imshow(all_images{i});
    shg;
    txt=sprintf('%d/%d: Was the consonent shown the same as N before?:', i, N);
    response= input(txt);
    if response== j|| response== k
        continue
    else
        disp('Letter pressed is not accepted')
    end
    fprintf(fid, 'stimuli: %d/t response: %s/n', i, response);
    fclose(fid);
end

Thank you for your help.

Answer 1

[madhan ravi]

response=input(txt,'s')
           %       ^^^---- missed it
doc input % read what 's' does   

Note: See when you enter j you don't get an error because matlab interprets j as an imaginary unit.

See https://www.mathworks.com/help/matlab/ref/i.html#bt4qta9-5

Further on while comparing characters use strcmp().

[madhan ravi]

if strcmp(response,'j') || strcmp(response,'k')

[Walter Roberson]

if ismember(response, 'jk')

[Guillaume]

While we're at it, the whole code starting at if doesn't make much sense. If the test had been correctly written, what would have happened is that if the user pressed 'j' or 'k', the loop would have continued at the next step (because of the continue) without displaying anything. If the user entered a different letter, then the code would display 'Letter pressed is not accepted' and then 'stimuli: xxx response: xxx'. Which doesn't make much sense. I suspect the whole thing should be:

f=figure(1);
for i=1:21
    imshow(all_images{i});
    shg;
    txt=sprintf('%d/%d: Was the consonent shown the same as N before?:', i, N);
    while true   %loop until user enters a valid response. We will break out of the loop when the response is valid
        response = input(txt, 's');  %'s': read input as text
        if isscalar(response) && ismember(response, 'jk')  %response must be a single character j or k
            break;
        end
        disp('Letter pressed is not accepted');  %we didn't break out of the loop. Warn the user and repeat input
    end
    fprintf(fid, 'stimuli: %d/t response: %s/n', i, response);
    fclose(fid);       %Is this supposed to be there?
end

There is also something wrong with the fclose(fid). At each iteration of the loop, a file is closed but it's never opened in the loop.

[madhan ravi]

Thank you sir Walter and Guillaume for narrowing it further!

[Kyle Davis]

Thank you everyone for your help, I really appreciate it, I understand where I was going wrong now!