Register Variables

How exactly do register variables work in C? When should they be used? K&R touches upon them briefly but moves right along. Is there any source in which I can read about them in depth?

>>12

So then a variable definition is a declaration that allocates storage for the variable

Informally a variable in C is a named object. However, there are a several trivial cases where the object doesn't have a name. 

Unless you can declare an extern variable within a function, then every variable declaration within a function is necessarily a definition

I think you just need to shut the fuck up something you clearly don't understand.