Question

How can i add files in fortran?

Answer 1

What do you mean "add files"?

If you mean perform file read/write operations then look at this tutorial on Fortran file handling: https://www.tutorialspoint.com/fortran/fortran_file_input_output.htm

If you mean to add a new file to your OnlineGDB project, then it's the same as with any other language, just click the NEW FILE icon, 2 to the left of the green RUN button.