different mode line info for different major modes?

I want to have column-number-mode turned on only for c-mode and no other major mode. How would I do this? When I add a hook to c-mode it changes mode line for every mode

Yes.

for some reason unknown to me, column-number-mode is a global minor mode. however, you can set the *variable* of the same name to nil locally in your c-mode buffers and it'll work. (add-hook 'c-mode-hook (lambda () (setq-local column-number-mode nil)))

For the record, that did seem to have the desired effect of encouraging the author to actually write a question (as opposed to the exceptionally vague "subject line and nothing else" that I'd been replying to).