Please help replace the integers in this function.

I have a function replaceMultiples that I am trying to write. it is supposed to take an input as a filename (fname) of a text file, and a natural number (num). Where each line of the text file contains one or more integers, separated by a blank space. Go through the text file fname line by line and replaces each integer that is a multiple of num by the integer divided by num. And write the modified text file to a text file with the same name as the original file, but started with ’updated# ’, where # represents the number num.

Here is my script so far:

function n=replaceMultiples2(fname, num)

ifh=fopen(fname,'r');   %open the file for reading
ofn=['updated_', num, fname]; %creates the output file name
ofh=fopen(ofn, 'wt');  %open the output file for writing
ln=' ';  %initiation of ln

while ischar(ln)
    ln=fgetl(ifh);
    if ischar(ln)
        ln=fgetl(ifh);  %grab the next line from the file
        while ~isempty(ln)
            [tk,ln]=strtok(ln);      %get the first token
            n=length(tk);
            i=1:1:n;
            if mod(str2num(tk(i))/num)==0; %calls integers divisable by num
                fprintf(ofh,' %s',tk); %write it to the input file

              else
                  fprintf(ofh, '%s ', tk);
              end
          end
          fprintf(ofh,'\n');
      end
  end
  fclose(ifh);
  fclose(ofh);

There are some errors. An example input would look like this:

replaceMultiples(’example.txt’,3)

Where the example text is this txt file:

123 571 −33
14 15 18
6 9
28 25 33 36

Then after inputting this into the function the new file should be called "updated3_example.txt" and should look like this:

41 571 −11
14 5 6
2 3
28 25 11 12

If someone could please help me fix my script so that it is functional I would really appreciate it. I dont think it is too far off from being functional. I believe my biggest problem right now is finding the correct way to test if the integer is divisible by n.

[Stephen23]

Duplicate, already with two answers:

https://www.mathworks.com/matlabcentral/answers/362280-i-need-help-replacing-the-integers-in-this-file