Having trouble with this problem

Here is the question:

The file upcs.txt contains a list of UPC codes that were scanned in a grocery store. Each line should, ideally, contain 12 digits corresponding to a single product. Read the contents of the file and store the entries into an m x 12 sized numeric array named codes, where m is the number of valid lines in the le. Lines that have less or more than 12 digits should be discarded. Some lines with 12 digits may have digits that were not correctly scanned, which were replaced by the letter X'. These missing digits should be represented in the array codes by the integer-1'. After processing the le, print the total number of lines read, the number of lines discarded, and the number of lines correctly processed and stored in codes.

upcs.txt:

X9096X082489

921642004330

810905023006

733554287763

413527622XX1

287X35871528

100093334850

764491079X90

1537X8886614

086755751640

860053705316

980098819206

038356338621

577577248178

82825685985

684580785580

736657539753

71113617151

935014271064

702345843488

58316491755

110118383664

333841856254

996003013296

495258095746

4457870230

684104168936

522784039910

6504512835

699553963094

853110488363

554147120089

Here is my code so far:

    fid = fopen('upcs.txt');
    mat = [];
    if fid == -1
        disp('File open was not successful')
    else codes = {};
        while feof(fid) == 0
            aline = fgetl(fid);
            num = strtok(aline);
            codes = [codes; num]
        end;
    [m n] = size(codes)
    discard = 0
    for i = 1:m
        len = length (codes(i))
        if len ~= 12
            codes = [];
            discard = discard + 1
        else
            char(codes(i))
            codes = strrep(codes, 'X', '-1')
        end
    end
    codes

    end

The trouble I am having is that I don't know how to delete the codes that have less or more than 12 digits in my code.

Answer 1

[Image Analyst]

I think your approach is all wrong. Don't add them all and then try to delete the bad ones. Just read a line and check it immediately. Only add it to your final array if it's good.

fid = fopen('upcs.txt');
if fid == -1
  disp('File open was not successful')
else
  codes = [];
  while feof(fid) == 0
    % Read one single line of text.
    singleLineOfText = fgetl(fid);
    % See if it has an X in it.
    xLocation = strfind(singleLineOfText, 'X');
    % Append it if it is exactly 12 characters long with no X in it.
    if length(singleLineOfText) == 12 && isempty(xLocation)
      codes = [codes; singleLineOfText];
    else
      fprintf('Discarding %s\n', singleLineOfText);
    end
  end
  % print out final codes to command window:
  fprintf('\nFinal codes = \n');
  codes
end