while loop requires explicit condition, for loop doesn't, why?

Question

In C++ you are allowed to have an empty condition inside the for-loop, for example as in for (;;) or for (int x = 0;; ++x). But you can't do while ().

When condition is omitted inside the for loop, condition is assumed to be true (so the loop loops forever). Why isn't this the case with while loops, that is, what's the argument behind not letting while () be an alias of while (true)?

Answer 1

Presumably, it's a side-effect of the fact that each given clause within the for-statement is optional. There's reasons why some for-loops wouldn't need an assignment; there's reasons why some others wouldn't need a condition; there's reasons why still others wouldn't need an increment. Requiring there to be some minimum number of them would be needlessly-added complexity.

Answer 2

The following is from the book Deep C Secrets:

Early C had no separate operators for & and && or | and ||. (Got that?) Instead it used the notion (inherited from B and BCPL) of "truth-value context": where a Boolean value was expected, after "if" and "while" and so forth, the & and | operators were interpreted as && and || are now; in ordinary expressions, the bitwise interpretations were used. It worked out pretty well, but was hard to explain. (There was the notion of "top-level operators" in a truth-value context.)

So there you have it, while() would set the context for a truth value and can't be empty or implied for the same reason if() can't be empty, the mechanics of the early language expected them not to be.