U

uint

A four-byte unsigned integral datatype.

ulong

An eight-byte unsigned integral datatype.

unchecked

A statement or operator that prevents arithmetic bounds from checking on an expression.

unsafe

A method modifier or statement that permits pointer arithmetic to be performed within a particular block.

ushort

A two-byte unsigned integral datatype.

using

Specifies that types in a particular namespace can be referred to without requiring their fully qualified type names. The using statement defines a scope. At the end of the scope, the object is disposed.