Interpret the matlab code - matlab

Question

I'm a Java programmer and have no background of matlab hence I'm really clueless with these lines of code from MATLAB. When I run the code I got an error :
??? Undefined function or variable 'nfile'.
Error in ==> texture_id at 29
fprintf(' \nneural network processing \n',nfile);
I understand that 'path' is a variable that stores string, 'demo' is boolean, but for the other lines, I don't want to assume what it does...Can you please help me and explain each lines?
Here's the code:
path = 'C:\Users\Dais\Documents\MATLAB\Data Sets\';
demo = true;
elfile = dir('*.jpg');
[lu ri] = size(elfile); feat=zeros(lu,29); nomf=cell(lu,1);
for nfi = 1:lu
nfile = elfile(nfi).name;
fprintf(' feature extraction file: %s \n',nfile);
nomf{nfi} = upper(nfile);
feat(nfi,:) = feature_ex([path nfile],demo);
end
fprintf(' \nneural network processing \n',nfile);

Answer 1

I would guess that whats happening here is that elfile = dir('*.jpg'); does not find any jpegs in the local directory and hence lu is empty and nfile is never populated. Place a breakpoint there in the code and check this. The way I would set up the loop would be something like this:
for nfi=1:numel(elfile)
As #Rody Oldenhuis said, use doc and help to elarn more about each function (or press F1 when the cursor is in the function name) but this should get you started..
%Looks for all files with extention .jpg in current directory
elfile = dir('*.jpg');
%lu and ri hold the rows, column lengths of elfile respectively
[lu ri] = size(elfile);
%creates an array of zeros of dimensions lu rows by 29 columns
feat=zeros(lu,29);
%creates an empty cell array (doc cell) dimensions lu rows by 1
nomf=cell(lu,1); columns
for nfi = 1:lu %look through all files
nfile = elfile(nfi).name; %get index nfi file
fprintf(' feature extraction file: %s \n',nfile); %print string
nomf{nfi} = upper(nfile); %upper case
feat(nfi,:) = feature_ex([path nfile],demo); %some external function
end
fprintf(' \nneural network processing \n',nfile); %print string

Answer 2

Rather than explain all and everything about MATLAB, I'll say this: MATLAB is interactive! And, one of the things why you pay good money for MATLAB, is that the documentation is awesome, and getting help is super easy.
For instance, you can type help <command> on the MATLAB command line, and get a short help on that command, or doc <command> to get the complete documentation, often with examples and demonstrations. The whole documentation is also online, should you prefer Google and being in a browser.
Should you have a script or function or class that has problems, you can issue dbstop if error, so that you drop into the debugger when an error occurs, and then you can view the contents of all variables just prior to the error, type new commands to investigate the error, etc. You can set breakpoints by clicking on the line number next to where you want to break, dbstep then makes a single step, dbup moves you up a level, etc. Have a look at doc dbstop.
You can select portions of code and press F9, which will execute those lines of code. Note that that is equivalent to copy-pasting the code to the command window and running it, so you will often have problems with undefined variables (and similar problems) that way (this or something similar is what I suspect happened in your particular case, as the code you posted should not give that error).