Digital filters

I've been wondering always how to implement filter in C language. There was a time when I just copied one IIR filter and tuned it to my needs but did not bother with discovering more about it and implement my own one. This springs back when I have to test a part where are few filters applied.

I have started with IIR and low pass filters.

Fixed Point Scaling [rowetel.com/blog]
This one explains simple low pass filter and provides octave file which helps me really weLL.  I will come back with octave topics later.
What is moving avarage filter? [dsprelated.com]
DSPrelated is the one which I visit when I look for digital signal processing. Articles, forum with many experienced users.
Introduction to Digital Filters [rw4.cs.uni-sb.de/~kaestner]

Low pass filter [helpful.knobs-dials.com]
This is moving avarage filter with code. Simple which enables reader to understand it quickly.

DSP Filters for touch sensing (bookmark)

I had to correct one IIR filter in touch sensing software because there was potentially one overflow in computing. This pdf from microchip contains few filters with C codes and figures how they affect the signal.
Various filters for touch sensing signals