Programming Languages - Chapter 5 Notes - Names, Bindings, Type Checking, and Scopes - Computer Science Now

⇑ Prog Languages

⇐ Chapter Notes

Chapter 5 Notes

Names, Bindings, Type Checking, and Scopes

§ 5.1 Introduction

§ 5.2 Names

T E R M S

identifier: The name of an item in a program.

¶ 5.2.1 Design Issues

Are names case sensitive?
Are the keywords of a language reserved words?

§ 5.3 Variables

T E R M S

variable: A named data container which can be both read and written in a program.

A variable can be described as:

A named storage location that can contain data that can be modified during program execution
A language object that may take different values, one at a time
A letter or other symbol used to represent a quantity.
A name that may be bound to a value.
A named item of data.
A symbol denoting a quantity or symbolic representation.
A name used to represent data that can be changed while the program or procedure is running.

§ 5.4 The concept of binding

T E R M S

binding: The association of a symbol with a value.
storage class: Property of an object that determines when the object comes into existence and goes out of existence.

¶ 5.4.1 Bindings of Attributes to Variables

¶ 5.4.2 Type Bindings

¶ 5.4.3 Storage Bindings and Lifetimes

T E R M S

static variable

§ 5.5 Type Checking

T E R M S

§ 5.6 Strong Typing

T E R M S

strong typing: A typing system which allows all type errors to be detected.
weak typing: A typing system which is not strong.

§ 5.7 Type Equivalence

T E R M S

§ 5.8 Scope

T E R M

scope: The portion of a program in which a particular identifier is visible.

¶ 5.8.1 Static Scope

T E R M

static scope: Scope which is determined at compile time.

¶ 5.8.2 Blocks

T E R M

block: (1) A section of program code which is syntactically grouped together.
(2) A physical data record, separated on the medium from other blocks by inter-block gaps.

In C, C++, C#, Java, JavaScript, PHP, and Perl, a block is a compound statement, enclosed by braces ({ ... }).
In Pascal, ADA, and Delphi, a block is a compound statement, enclosed by begin ... end keywords.

¶ 5.8.3 Evaluation of Static Scoping

¶ 5.8.4 Dynamic Scope

T E R M

dynamic scope: Scope which is determined at run time.

¶ 5.8.3 Evaluation of Dynamic Scoping

§ 5.9 Scope and Lifetime

T E R M S

lifetime: The period during execution of a program in which a variable or function exists.

Scope and lifetime are not the same thing!
The lifetime of a static variable is the lifetime of the program execution, regardless of the scope of the variable.
The scope of a local variable is the block in which it is declared, regardless of its storage class.
The lifetime of an automatic variable is the lifetime of the subprogram execution.
The lifetime of a controlled variable is determined programmatically, regardless of its scope.

5.10 Referencing Environments

T E R M S

referencing environment: The collection of all names that are visible in the statement.
static referencing environment: The set of all the unique variables declared in the static ancestors of a subprogram or statement.
dynamic referencing environment: The set of all the unique variables declared in the dynamic ancestors of a subprogram or statement.

§ 5.11 Named Constants

T E R M S

constant: A value that cannot change;
named constant: A variable whose value cannot be changed by the program after initialisation.
literal constant: A lexical token that directly represents a scalar value of intrinsic type.
manifest constant: A symbolic constant with a predefined value.
soft coding: The use of named constants in program code.
hard coding: The use of literal constants in program code.

Literal constant examples:

432
3.14159
"Hello"
'C'

The value of a literal constant is explicitly given by its representation.
Named constant examples:

const int RoomCapacity = 432;
const double pi = 3.14159;
const char * Greeting = "Hello";
const char Closed = 'C';

Named constants are typically related to the problem environment for the program.
Manifest constant examples:

EXIT_SUCCESS
EOF
MAX_INT

Manifext constants are typically related to the environment of the program - the operating system, the compiler, the hardware, etc.
Soft coding has several advantages:

Soft coding makes a program more readable, assuming that constants are given meaningful names.
Soft coding makes a program more maintainable, since the value of a named constant appears only once in a program. (A literal constant may occur multiple times in a program, making it problematic to change all instances.)

Terms

See Also

C++ Variables

External Links

Manifest Constants

See Also

Chapter 4	Lexical and Syntax Analysis
Chapter 6	Data Types

copyright 2007, j.h.young, revised 10/16/2007