The real difference between “int” and “unsigned int”

Question

int:

The 32-bit int data type can hold integer values in the range of −2,147,483,648 to 2,147,483,647. You may also refer to this data type as sig

Answer 1

The problem is that you invoked Undefined Behaviour.

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When you invoke UB anything can happen.

The assignments are ok; there is an implicit conversion in the first line

int x = 0xFFFFFFFF;
unsigned int y = 0xFFFFFFFF;

However, the call to printf, is not ok

printf("%d, %d, %u, %u", x, y, x, y);

It is UB to mismatch the % specifier and the type of the argument.
In your case you specify 2 ints and 2 unsigned ints in this order by provide 1 int, 1 unsigned int, 1 int, and 1 unsigned int.

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Don't do UB!