Literal types: 0x1ull vs 0x1llu

Question

My gcc compiler allows me to define an unsigned long long (i.e. 64-bit) literal as

#define A_LITERAL 0x1ull

--- or ---

Answer 1

ull or llu force the compiler to treat a constant as an unsigned and long long integer.
The order of ll and u doesn't matter, nor their case. you may also write LLU or ULL.