How to include a variable in "fopen" file name in a For loop?

Dear members,

This code edits a certain number in an input text and generates a new output file containing the new edited number. I want to generate many output files but the problem is that each time a new output file is generate it replaces the previous one since they will have the same name. I want to include a variable in the name that changes each time the code loops.

So I need to edit this line: f2d = fopen('output_matlab_i.txt','wt') where i will be variable from 1 to s and thus we will get: output_matlab_1, output_matlab_2, output_matlab_3...

Any help?

Thank you!

 phi_rnd=lognrnd(log((m^2)/sqrt(std^2+m^2)),sqrt(log(std^2/(m^2)+1)),1,n)
 indices = find(abs(phi_rnd)<28);
 phi_rnd(indices) = [];  
 s=size(phi_rnd,2);
 
 for i=1:s
    vec=zeros(1,2); 

    vec = [phi_rnd(1,i),phi_rnd(1,i)];
    cnt = 0;
    rgx = '^(\s*\S+\s+)(\S+)(.+gamma.+)$';
    f1d = fopen( 'input_matlab.txt','rt');
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    f2d = fopen('output_matlab.txt','wt');%>>>>>This is the line to be edited
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    while ~feof(f1d)
    str = fgetl(f1d);
    tkn = regexp(str,rgx,'once','tokens');
    if ~isempty(tkn)
        cnt = cnt+1;
        str = sprintf('%s%#.14E%s',tkn{1},vec(cnt),tkn{3});
    end
    
    fprintf(f2d,'%s\n',str);
    
    end
    fclose(f1d);
    fclose(f2d);
   
 end

Answer 1

[Fangjun Jiang]

for k=1:5
FileName=sprintf('output_matlab_%d',k)
end

[Ahmad Fakih]

But how can I fit this into my code?

[Walter Roberson]

FileName = sprintf('output_matlab_%d.txt', i);
f2d = fopen(FileName, 'wt');

[Ahmad Fakih]

Thank you Walter and Fangjun!