Having trouble using auto-complete in emacs

Question

I've installed auto-complete inside emacs using elpa and have used M-x auto-complete-mode to check that it is enabled. However when I write the following short C code in emacs and put my cursor in front of the v and press the TAB key nothing happens.

Is this not the correct key or is there something wrong with my setup?

int main(void){
  varA = 5;
  varB = 7;

 v

 return 0;

}

The contents of my .emacs.d/elpa/ directory are:

• archives
• auto-complete-20160329.2321
• popup-20160409.2133

And my emacs.d/init.el contains

(custom-set-variables
 ;; custom-set-variables was added by Custom.
 ;; If you edit it by hand, you could mess it up, so be careful.
 ;; Your init file should contain only one such instance.
 ;; If there is more than one, they won't work right.
 '(inhibit-startup-screen t))
(custom-set-faces
 ;; custom-set-faces was added by Custom.
 ;; If you edit it by hand, you could mess it up, so be careful.
 ;; Your init file should contain only one such instance.
 ;; If there is more than one, they won't work right.
 )
(require 'package) ;; You might already have this line
(add-to-list 'package-archives
             '("melpa" . "https://melpa.org/packages/"))
(when (< emacs-major-version 24)
  ;; For important compatibility libraries like cl-lib
  (add-to-list 'package-archives '("gnu" . "http://elpa.gnu.org/packages/")))
(package-initialize) ;; You might already have this line

(require 'auto-complete)
(global-auto-complete-mode t)

(require 'auto-complete-config)
(ac-config-default)

Answer 1

Drew helped me solve it, you need to type more than 1 character for the auto-complete window to appear, it is installed ok, just wasn't using it correctly. This makes sense since you might be wanting to type int or something and wouldn't want a window to come up every time you typed a single character.