Question

int a = 17 (=10001)

int b=5 (101)

a&b      1         bitwise AND
a|b     21         bitwise OR
a^b     20         XOR (16+4) “just one”
a&&b     1         logical AND
a||b     1         logical OR
-b      -5         minus b
~b       -6         ?
~(~a)      17        ?
!b       0         logical “NOT B”
!(!a))   1         logical “NOT NOT A”
a=b      0         “a==b?”
a=’A’   65         ?
a|’@’   64         ?

Can you please help me explain the parts where the ? is.

Answer 1

~b       -6         ?

The “~” flips all the bits, and negative numbers are represented using something called 2s complement. The -6 is just what happens when you flip all the bits of “5”: you get a different bitpattern, which is the same bits as “-6” in 2s complement.

~(~a)      17        ?

Similar. Flip all the bits, then flip all the bits again, and what do you get? The same as before.

a=’A’   65         ?

Internally, characters are represented by numbers, just like everything else in a computer. Virtually all these number<->character tables in use today are based on ASCII, and ‘A’ just happens to have the number 65 in the ASCII table.

a|’@’   64         ?

That doesn’t make sense. ‘@’ is 64 (ASCII, again), which is hex 0x40. 0x40 | 17 should be 81.