Is C a great language, or what? Where else could you write something like a+++++b ?

Well, you can't meaningfully write it in C, either. The rule for lexical analysis is that at each point during a straightforward left-to-right scan, the longest possible token is determined, without regard to whether the resulting sequence of tokens makes sense. The fragment in the question is therefore interpreted as

a ++ ++ + b

and cannot be parsed as a valid expression.