Using fprintf to specify a filename for write to text file in loop

I am creating a number of text files (or really m files) in a loop. The filenames should be sequential, having the suffix 1,2,3... I wanted to use fprintf to specify the filename in the loop. However, I get the error in line 2: "invalid filename." How can I achieve what I am trying to do? I've pasted an example code below.

for k=1:25

      fid = fopen(fprintf('K_a_12_%dx.m',k),'w');
      fprintf(fid, 'function [K_a_12]=K_a_12_%dx(G_a,E_a,h_a)\n',k);
      fprintf(fid, 'K_a_12=zeros(10,100)\n');

      for i=(1+(k-1)*10):(k*10);
          for j=1:100;
                  fprintf(fid, 'test');
          end
      end

      fclose(fid);

end

Answer 1

[dpb]

Use sprintf instead--*fprintf* w/o a unit number writes to screen so you're left w/ nothing in the filename location.

fid = fopen(sprintf('K_a_12_%dx.m',k),'w');

I'd suggest if you're creating files w/ such numbering systems to use the leading zeros in a fixed width field for the numbering. Then you'll get a collated ordering based on numeric order instead of collating order automagically...that is, make the format string

fn = sprintf('K_a_12_%3.3dx.m',k);
fid = fopen(fn,'w');

Using the separate filename in the fopen is matter of taste; building it separately can help in debugging during development if on then wants to fold it into the fopen can...

Answer 2

[Kobye]

I've figured it out... had to use sprintf instead of fprintf.