u
means unsigned
, so ulong
is a large number without sign. You can store a bigger value in ulong
than long
, but no negative numbers allowed.
A long
value is stored in 64-bit,with its first digit to show if it's a positive/negative number. while ulong
is also 64-bit, with all 64 bit to store the number. so the maximum of ulong is 2(64)-1, while long is 2(63)-1.