I know people who seem to delight in using all the C tricks and produce code which is not clear even to them.The thing which does cause the most confusion and which few books actualy offer a clear explaination of is the if(a=b) assignment and yet its often seen in code is always going to throw anyone reading it.
The confusion arrises because there are two types of compares you can do with if, the normal one is if(a==b)... which compares a to b and returns true if they are equal and the conditional code after the if is executed, if(a=b) assigns b to a and if b is not 0 it returns true and the condition code after the if is executed.this is a common mistake for beginners to type if (a=b) when they really want a compare not an assignment,one way to make sure that the mistake is spotted at compile time is to use the inverted compare i.e. if(2==a)... which will produce a compiler error if you mistakenly type if(2=a) mind you people who remember to use the inverted compare will probably remember to type == rather than = anyway.
The statement [(rpos+rcnt++) % RBUFLEN] calculates (rpos+rcnt) modulo RBUFLEN and then increments rcnt.
You cannot use if(a=b) in C++ unless a and b are both boolean types.