ALL OF THE SAMPLE CODE YOU'VE SEEN so far has been self-contained C versions of code you could have already written in PHP userspace. If the project you've got in mind is anything like most PHP extensions, however, you're going to want to link against at least one external library.
The PHP Life Cycle
Variables from the Inside Out
Memory Management
Setting Up a Build Environment
Your First Extension
Returning Values
Accepting Parameters
Working with Arrays and HashTables
The Resource Data Type
PHP4 Objects
PHP5 Objects
Startup, Shutdown, and a Few Points in Between
INI Settings
Accessing Streams
Implementing Streams
Diverting the Stream
Configuration and Linking
Extension Generators
Setting Up a Host Environment
Advanced Embedding
Appendix A. A Zend API Reference
Appendix B. PHPAPI
Appendix C. Extending and Embedding Cookbook
Appendix D. Additional Resources