The examples in this book are quite important. At the very least, you should skim them, acquiring a good idea of what they do and a fundamental understanding of how they work. This text presents many concepts that seem somewhat awkward in words alone but are clear when presented in conjunction with an example.
In the continuing effort to keep this book's page count down, many of the examples here are not complete valid C programs. The first few chapters contain primarily short multiline fragments , demonstrating function calls described in the surrounding text. There are many full programs within the text, though, and you can get them at http://www.nostarch.com/gnome.htm .
If you come across a variable that doesn't seem to have a declaration and you don't know its type or significance, take a look at the previous pages; you should find it there. For instance, the listings accompanying the description of GList don't always contain the line
When a preprocessor directive such as #include appears just before some function calls, then you must use the directive somewhere at the beginning of your source code. This is similar to the style of the online Unix programming manual; run man gethostbyname and look at the SYNOPSIS section.