printing a boolean value in c++

Question

When I run this simple code,

int main(int argc, const char * argv[])
{
      bool digit(true);
      std::cout << digit << " " << ~digit << std::endl;
}

The output is

1 -2

I was expecting 1 and 0 (for true and false). Am I missing something here?

Answer 1

~ performs bitwise negation. The operand is promoted (in this case) to int, and all the bits are inverted. 1 has a binary representation of 00....001, so this gives the binary value 11....110, which is interpreted (on most modern computers) as -2.

Use ! for logical negation.

Answer 2

~ is the bitwise not (or bit inversion) operator. The logical not operator is '!'.

    cout << !digit;