Flymake Tutorial

You need to have a C file you will be editing, with its respective Makefile already in the directory. Your Makefile should include the following for flymake to use

.PHONY: check-syntax

check-syntax:
    $(CC) $(CFLAGS) -Wall -Wextra -0pedantic -fsyntax-only $(SRCS)

Make sure you use a <TAB> under the target!

Place the following code in your emacs init file

;; Customize how flymake displays the errors
'(flymake-errline ((((class color)) (:underline "OrangeRed"))))
'(flymake-warnline ((((class color)) (:underline "yellow"))))

;; Define our own flymake error function
(defun my-flymake-show-next-error ()
  (interactive)
  (flymake-goto-next-error)
  (flymake-display-err-menu-for-current-line))

;; And set it to the shortcut C-c C-v
(add-hook 'c-mode-common-hook
  (lambda ()
    (flymake-mode t)
    (global-set-key "\C-c\C-v" 'my-flymake-show-next-error)))

This will set C-c C-v to show the next error in your c files, and makes the errors display a little more clearly.