How to use index in the file name

Question

This is probably trivial question. I am not a professional programmer, I am rather a mathematician who is doing some numerical experiment using C. I would like the output of my

Answer 1

You can just build a string up with sprintf. Make sure your buffer is large enough:

char filename[20];
sprintf( filename, "file%d", i );

Then you can open it like this:

FILE *f = fopen( filename, "w");
...
fclose(f);

No need to use an array (if that's what you were trying to do with f(i)), because you're only keeping one file open at a time.

If you want your files to be text-sortable, you might want file001, file002 etc... You can use %03d instead of %d to 0-pad to 3 digits.