Answer 1

It is similar for -1<<4

Arithmetic left shift ¹: shifting `-1` in two's complement ² representation to left by one as

-1 << 1

At binary level (32-bit words) we have:

1 =
0000 0000 0000 0000 0000 0000 0000 0001

-1 =
1111 1111 1111 1111 1111 1111 1111 1111

and by doing

1111 1111 1111 1111 1111 1111 1111 1111 << 1

we get

1111 1111 1111 1111 1111 1111 1111 1110 = -2 in decimal

And "%x" specifier would nicely format the hexadecimal representation of the above bit sequence [converts an unsigned integer into hexadecimal representation hhhh. ³]. Every 4 bits comprise one hex digit. So the total hex numbers are 8 as

fffffffe or FFFFFFFE (for "%X")
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¹ https://en.wikipedia.org/wiki/Arithmetic_shift
² https://en.wikipedia.org/wiki/Two%27s_complement
³ https://en.cppreference.com/w/cpp/io/c/fprintf