Something nobody has mentioned yet is that, in the C-style version, the precedence rules are eliminating some parentheses. You can't do that in Lisp (except maybe with a macro). But then, in Lisp, you don't have to remember precedence rules.

In this example, the advantage is on the C side, because pretty much everybody who knows any math knows that multiplication has precedence, and they can just read that syntax. If you have to go look at the precedence chart in K&R or Stroustrup before you know how to parse the expression correctly, well, then the Lisp approach is probably more efficient...