hi all,

ok, so on page 86 under the section Bitwise NOT, we have a working example of using ~ on the variable letter1, which is 65 which is represented as:

0000 0000 0000 0000 0000 0000 0100 0001

in the book it says ~letter1 = 190, but how can that be if i invert it i get:

1111 1111 1111 1111 1111 1111 1011 1110 which is significantly larger than 190. Now what makes things even more confusing is that on my pc i get -66?

Now i know that letter1 is declared as a char so its only 8 bits, but i've tried making letter1 an int and it gives me the same result. ive noticed that coverting any positive integer like 4 or 7 will give me -5 or -8 respectively, but when using the bits that cant possibly make sense..

anyone got any ideas?


thanks a mil!!

Hi,
I know it's old thread, but if you still don't know the answer then I think it's the type of character value, if you try inverting unsigned char 'A' (65) it will
give you 190.
It's still weird though, I can't get why when you type:

int main()
{
unsigned char sample = 'A';
cout << static_cast<int>(sample) << endl;
unsigned char sample2 = ~sample;
cout << static_cast<int>(sample2) << endl;
cout << static_cast<int>(~sample) << endl;
return 0;

}
you will get output:
65
190
-66

I don't get why when for static_cast function I use rvalue ~sample it still gives -66 . I think after checking: ~sample also would give -66 so I guess operator ~ implicitly converts sample to type signed char before reversing bits and then outputs as int.

Analyze the output of the below so it may make it more clear for you:
unsigned char sample = 'A';
cout << static_cast<int>(sample) << endl;
unsigned char sample2 = ~sample;
cout << static_cast<int>(sample2) << endl;
cout << static_cast<int>(~sample) << endl;
cout << sample << endl;
cout << ~sample << endl;
cout << sample2 << endl;
return 0;

Now I have also tried below lines and it worked so I guess you need to explicitly convert your value to unsigned char by any means:

cout << static_cast<int>(static_cast<unsigned char>(-66)) << endl;
cout << static_cast<int>(static_cast<unsigned char>(~sample)) << endl;

I hope this helps.

thanks, i will have a look at this code and see if it helps

:)