If you ever want to learn to write externals for Max, I would recommend starting out by learning to write Java classes for the mxj object. It’s a good way of learning what needs to be in the code for the external while avoiding the more nitty gritty details of C coding.
mxj and Java is truly great for prototyping code and externals. The screenshot above is of a patch and class I made yesterday as prototype/proof of concept code for Espen Sommer Eide to solve a particular task in an iPad app that he is currently developing.