Create a file containing the complete program, such as the above example. You can use any ordinary editor with which you are familiar to create the file. One such editor is emacs.
The filename must by convention end ``.c'' (full stop, lower case c), e.g. myprog.c or progtest.c. The contents must obey C syntax. For example, they might be as in the above example, starting with the line /* Sample .... (or a blank line preceding it) and ending with the line }/* end of program */ (or a blank line following it).