Let's get more people programming free software. I do it as part of my work, but it can be done avocationally too. I do it outside of work whenever possible. My two favourite books for the purpose;
https://en.wikipedia.org/wiki/The_C_Programming_Language
https://web.archive.org/web/20150426092105/http://www.ccs.neu.edu/home/matthias/BTLS/