c++ - tilde operator returning -1, -2 instead of 0, 1 respectively

Question

I'm kind of puzzled by this. I thought the ~ operator in C++ was supposed to work differently (not so Matlab-y). Here's a minimum working example:

#include <iostream>
using namespace std;
int main(int argc, char **argv)
{
    bool banana = true;
    bool peach = false;
    cout << banana << ~banana << endl;
    cout << peach << ~peach << endl;
}

And here's my output:

1-2
0-1

I hope someone will have some insight into this.

Answer 1

This is exactly what should happen: when you invert the binary representation of zero, you get negative one; when you invert binary representation of one, you get negative two in two's complement representation.

00000000 --> ~ --> 11111111 // This is -1
00000001 --> ~ --> 11111110 // This is -2

Note that even though you start with a bool, operator ~ causes the value to be promoted to an int by the rules of integer promotions. If you need to invert a bool to a bool, use operator ! instead of ~.