How to write a `for` loop over bool values (false and true)

Solution 1:

In C++11: for (bool b : { false, true }) { /* ... */ }

Here's a C++03 version:

for (bool a = true, b = false; b != a; a = a && b, b = !b) { /*...*/ }

(Use either a or b.)

Solution 2:

When restricted to C++2003 you could use an approach roughly equivalent to the C++2011 approach;

{
  bool const bools[] = { false, true };
  for (bool const* it(bools); it != std::end(bools); ++it) {
      bool a(*it);
      use(a);
  }
}

Possibly packed up in a macro. You can also use

for (bool a: { false, true }) {
    use(a);
}

Solution 3:

for (int a = 0; a <= 1; a++)
  doStuff(a ? true : false);

And forget about "no conversions to other types" restriction :) In the end of the day clarity is more important than artificial restrictions. Five years down the line you'll be reading your own code and wondering "what the heck was I thinking, is this some sort of an obfuscation contest?"

Solution 4:

a = true;
do {
  use(a);
  a = !a;
} while (!a);

OK, so it's not a for loop, but I would argue it is more readable than any of the for loop suggestions (other than the C++11 approach, of course.)

Solution 5:

One more for C++03:

for(bool a = false, b = true; b; a = !a, b = a)  

Use b.