From LQWiki

Here are some examples that are intended to help the "I know next to nothing about C" programmer getting started. Also be sure to check out C/C plus plus tips which includes some more advanced information.

• Hello World in C, the example program for those who really do know nothing about C.
• Pi in C, A small program that computes the value of Pi.
• Connecting a socket in C, shows how you can connect your program to any remote computer and see if it sends anything to you. For instance a web-server.
• Duff's device Don't try this one at home.