Date: Oct 19, 2011 4:40 AM
Author: mailcwc@gmail.com
Subject: Clear all variables but not functions

I define some functions in the init.m that starts with Mathematica.
How do I clear all variables but not these functions in the init.m?

I am also confused about the differences among Remove, Clear,
ClearAll, and Quit.
Are there some cases that one function is preferred than others.