Exercise 22: The Stack, Scope, and Globals

The concept of scope seems to confuse quite a few people when they first start programming. It originally came from the use of the system stack (which we lightly covered earlier), and how it was used to store temporary variables. In this exercise, we'll learn about scope by learning how a stack data structure works, and then feeding that concept back in to how modern C does scoping.

The real purpose of this exercise, though, is to learn where the hell things live in C. When someone doesn't grasp the concept of scope, it's almost always a failure in understanding where variables are created, exist, and die. Once you know where things are, the concept of scope becomes easier.

This exercise will require three files:

• ex22.h: A header file that sets up some external variables and some functions.
• ex22.c: This isn't your main like normal, but instead a source file that will become the object file ex22.o, which will have some functions and variables in it defined from ex22.h.
• ex22_main.c: The actual main that will include the other two, and demonstrate what they contain, as well as other scope concepts.