值类型 - ushort uint ulong（无符号 16 位 32 位 64 位整数）

// assigning an unsigned short to its minimum value
ushort s = 0;

// assigning an unsigned short to its maximum value
ushort s = 65535;

// assigning an unsigned int to its minimum value
uint i = 0;

// assigning an unsigned int to its maximum value
uint i = 4294967295;

// assigning an unsigned long to its minimum value (note the unsigned long postfix)
ulong l = 0UL;

// assigning an unsigned long to its maximum value (note the unsigned long postfix)
ulong l = 18446744073709551615UL;

也可以使这些类型可以为空，这意味着除了通常的值之外，还可以分配 null。如果未初始化可空类型的变量，则它将为 null 而不是 0.可以通过在类型后添加问号（？）来标记可空类型。

uint a; //This is now 0.
uint? b; //This is now null.