tags: Identifiers that represent a declaration of the data types struct , union , or enum . You may use tags in declarations from that point onward in the program to declare other variables of the same type without having to key in the lengthy declaration again.

tokens: The fundamental elements making up the text of a C program. Tokens are identifiers, keywords, constants, strings, operators, and other separators. White space (such as spaces, tabs, new lines, and comments) is ignored except where it is necessary to separate tokens.

type: The attribute that, with its storage class, determines the meaning of the values found in the identifier's storage. Types include the integral and floating types, pointers, enumerated types, the void data type, and the derived types array, function, structure, and union .

type name: The declaration of an object of a given type that omits the object identifier. A type name is used as the operand of the cast and sizeof operators.

unary operator: An operator that takes a single operand. In C, unary operators either precede or follow the operand. The set includes the asterisk (indirection), ampersand (address of), minus (arithmetic unary minus), exclamation (logical negation), tilde (one's complement), double plus (increment), double minus (decrement), cast (force type conversion), and sizeof (yields the size, in bytes, of its operand) operators.

union: A union is an aggregate type that can be considered a structure, all of whose members begin at offset 0 from the base, and whose size is sufficient to contain any of its members. A union can only contain the value of one member at a time.

uniqueness: A property of the names used for certain structure and union members. A name is unique if either of the following conditions is true:

• The name is used only once.
• The name is used in two or more different structures (or unions), but each use denotes a member at the same offset from the base and of the same data type.

The significance of uniqueness is that a unique member name can possibly be used to refer to a structure in which the member name was not declared (although a warning message is issued).

variable: An identifier used as the name of an object.

value: The result of an expression. For example, when a variable on the right side of an assignment expression is evaluated, the value obtained is the object (rvalue) of the variable; when a variable on the left side of an assignment expression is evaluated, the value obtained is the address (lvalue) of the variable.

white space: Spaces, tabs, new lines, and comments. The compiler defines where you can and cannot place these characters.

windows: In the Curses Screen Management package, the defined rectangular regions on the terminal screen that you can write upon, rearrange, move to new positions on the screen, and delete from the screen. You define windows by specifying the upper left corner coordinate, the number of lines, and the number of columns comprising the window. To see the results after editing a window, you must refresh the window on the terminal screen. See also refresh.

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