After a long time confuse and break, I am back and ready for working enthusiastically

It is very important for now to make sure some special usages of C++ programming philosophy and its library staff.

First of all is the usage of size_t, why did not they use the int or long to represents the number instead of using size_t. I believe it is explained well in article of :

http://www.embedded.com/columns/programmingpointers/200900195

and 

http://ubuntuforums.org/showthread.php?t=898189

very useful articles.