Earlier I mentioned that variables can live in two different places. We're going to examine these two places one at a time, and we're going to start on the more familiar ground, which is called the Stack. Understanding the stack helps us understand the way programs run, and also helps us understand scope a little better.

This will allow us to use a few functions we didn't have access to before. These lines are still a mystery for now, but we'll explain them soon. Now we'll start working within the main function, where favoriteNumber is declared and used. The first thing we need to do is change how we declare the variable. Instead of

This back and forth is an important concept to understand in C programming, especially on the Mac's RISC architecture. Almost every variable you work with can be represented in 32 bits of memory: thirty-two 1s and 0s define the data that a simple variable can hold. There are exceptions, like on the new 64-bit G5s and in the 128-bit world of AltiVec

Since the Heap has no definite rules as to where it will create space for you, there must be some way of figuring out where your new space is. And the answer is, simply enough, addressing. When you create new space in the heap to hold your data, you get back an address that tells you where your new space is, so your bits can move in. This address is called a Pointer, and it's really just a hexadecimal number that points to a location in the heap. Since it's really just a number, it can be stored quite nicely into a variable.

Inside each stack frame is a slew of useful information. It tells the computer what code is currently executing, where to go next, where to go in the case a return statement is found, and a whole lot of other things that are incredible useful to the computer, but not very useful to you most of the time. One of the things that is useful to you is the part of the frame that keeps track of all the variables you're using. So the first place for a variable to live is on the Stack. This is a very nice place to live, in that all the creation and destruction of space is handled for you as Stack Frames are created and destroyed. You seldom have to worry about making space for the variables on the stack. The only problem is that the variables here only live as long as the stack frame does, which is to say the length of the function those variables are declared in. This is often a fine situation, but when you need to store information for longer than a single function, you are instantly out of luck.