Using C in Linux, would it be possible to change the brightness of the viewing screen? This isn't expected to be portable other than running on my installs of Ubuntu and Fedora. I'm asking about how I would interface with the os to change the brightness.
I'd start with selecting from the following list of ubuntu pacakges, the tool that allows you to manage your screen's brightness (hint: it depends on the brand)
nvidia-settings - Tool of configuring the NVIDIA graphics driver smartdimmer - Change LCD brightness on Geforce cards armada-backlight - adjust backlight of Compaq Armada laptops (E300, M500, M700) ddccontrol - a program to control monitor parameters eeepc-acpi-scripts - Scripts to support suspend and hotkeys on the Asus Eee PC laptop fnfxd - ACPI and hotkey daemon for Toshiba laptops gddccontrol - a program to control monitor parameters spicctrl - Sony Vaio controller program to set LCD backlight brightness tpb - program to use the IBM ThinkPad(tm) special keys xfce4-power-manager - power manager for Xfce desktop xfce4-power-manager-plugins - power manager plugins for Xfce panel xvattr - Utility to change Xv attributes
Once you have selected it,
sudo apt-get build-dep <pkgname> apt-get source --compile <pkgname>
should get you on the right track