On Thu, Dec 03, 2020 at 02:20:50AM -0800, John Conover wrote:
> Possible to set c mode for *.ino files?

Most easily you can add the association ".ino" => c-mode to your
variable `auto-mode-alist', perhaps in your init file. The left
hand side of the association is a regular expression which has
to match the file names; in this case, perhaps something like
"\\.ino\\'". Something like

  (add-to-list 'auto-mode-alist c-mode)

in your init file might do.

Alternatively, you could put something like

/* -*- mode: c -*- */

somewhere at the top of your files.

For all the other possibilities and their ramifications, see
"23.3 Choosing File Modes" in the manual; in the Interwebs
here [1].

Cheers

[1] https://www.gnu.org/software/emacs/manual/html_node/emacs/Choosing-Modes.html

 - t