Source:
What happens if I assign a negative value to an unsigned variable?
Q:
What happes if I do
unsigned int n = -1;A:
Section 4.7 If the destination type is unsigned, the resulting value is the least unsigned integer congruent to the source integer (modulo 2^n where n is the number of bits used to represent the unsigned type). [ Note: In a two’s complement representation, this conversion is conceptual and there is no change in the bit pattern (if there is no truncation)
so it's 0xFFFFFFFF (on a machine defining unsigned as 32 bits);