How can I fix my function?

function numReplaced=replaceMultiples(fname,num)
    clc
    num=0
    fname='example.txt';
    ifn=fname;
    ofn=['updated%d %s',num,fname];
    ifh=fopen(ifn,'r'); % open the file for reading
    ofh=fopen(ofn,'wt'); %open the output file for writing
    ln=fgetl(ifh); % try to get the first line of the file
    while str2num(fname)
        while ~isnan(num)
            [tk,ln]=strtok(ln); 

              if mod(fname,num)==0
              fprintf(ofh,'%s ',tk); %write to output file  
            end

          end
          fprintf(ofh,'\n'); %after the complete line has

          ln=fgetl(ifh);
      end
      fclose(ifh); % close the file
      fclose(ofh);

Answer 1

[Walter Roberson]

Do not assign to fname or num in your code.

str2double(fname) is attempting to interpret the file name itself as a number.

Your code is converting file contents into tokens but it then tries to take modulo on the file name itself instead of examining the content it tokenized.