Can I use the logical not operator on integers?

Question

Can you use the ! operator for int in C++? For example:

#include <iostream>

int main()
{
   int a=5, b=4, c=4, d;
   d = !( a > b && b <= c) || a > c && !b;
   std::cout << d;
}

Answer 1

Yes. For integral types, ! returns true if the operand is zero, and false otherwise.

So !b here just means b == 0.

---

This is a particular case where a value is converted to a bool. The !b can be viewed as !((bool)b) so the question is what is the "truthness" of b. In C++, arithmetic types, pointer types and enum can be converted to bool. When the value is 0 or null, the result is false, otherwise it is true (C++ §4.1.2).

Of course custom classes can even overload the operator! or operator<types can be convert to bool> to allow the !b for their classes. For instance, std::stream has overloaded the operator! and operator void* for checking the failbit, so that idioms like

while (std::cin >> x) {   // <-- conversion to bool needed here
  ...

can be used.

(But your code !( a > b && b <= c) || a > c && !b is just cryptic.)