Coding Theory is the area of maths that I'm researching and writing my doctoral thesis on. Essentially it's all about achieving efficient information transmission (or storage) by adding or removing redundancy.
C is also for Ceol - the Irish word for music. Each year as part of National Irish Week (Seachtain na Gaeilge) there is an album released of popular music with Irish language lyrics instead. The 96cambridge channel on youtube has some of the songs from these.
For a mathematician we have Cauchy- one of the most prolific mathematicians of all time with almost 800 papers.His name appears frequently and in many seemingly disparate branches of maths.
As mentioned before C is for Commutative. In maths we say an operation * is commutative whenever a * b = b * a. Addition and multiplication are commutative but subtraction and division are not.
Honourable mentions go to Crochet, Cryptography and Calves that ache after dancing my socks off at the wedding!