Answer 1

The basic idea is that -1 is not in the range of unsigned long and therefore a conversion is needed, producing the value code 1 printed. In code 2 you convert the value converted to unsigned long back to int (2 conversions, one in initialization and the other in printf()), resulting the same value -1.

Answer 2

%d = Signed Integer

%lu = Unsigned integer

source: https://codeforwin.org/2015/05/list-of-all-format-specifiers-in-c-programming.html

Answer 3

unsigned integers are nonnegative. assigning a negative to an unsigned variable causes undefined behavior

Prince if you knew that, why ask?