Chapter 5

Question 1

What are the design issues for names?

Answer 1

The primary design issues are whether names are case sensitive and whether the special words of the language are reserved words or keywords .

Question 2

What is the potential danger of case-sensitive names?

Answer 2

They hurt readability because similar-looking names (like Rose and rose) mean different things.

Question 3

In what way are reserved words better than keywords?

Answer 3

Reserved words cannot be redefined, preventing confusion; keywords can be redefined.

Question 4

What is an alias?

Answer 4

When two or more variable names access the same memory location.

Question 5

Which category of C++ reference variables is always aliases?

Answer 5

Reference variables and dereferenced pointers that point to the same location are always aliases

Question 6

What is the l-value?

Answer 6

The address of a variable used on the left side of an assignment.

Question 7

What is the r-value?

Answer 7

The value of a variable used on the right side of an assignment.

Question 8

Define binding.

Answer 8

Connecting an attribute to an entity.

Question 9

Define binding time.

Answer 9

The moment when a binding occurs.

Question 10

When can bindings take place?

Answer 10

Compile time, link time, load time, run time.

Question 11

Define static binding and dynamic binding.

Answer 11

Static Binding: Occurs before run time and stays unchanged throughout execution.

Dynamic Binding: Occurs during run time or can change during execution

Question 12

What are the advantages and disadvantages of implicit declarations?

Answer 12

Advantage: It is a minor convenience for programmers.

Disadvantage: It hurts reliability because the compiler cannot detect typo errors (e.g., misspelling a variable name creates a new variable instead of an error)

Question 13

What are the advantages and disadvantages of dynamic type binding?

Answer 13

Advantage: Provides great programming flexibility (e.g., writing generic code).

Disadvantages: It makes programs less reliable (error detection is lost) and increases the cost of execution time.

Question 14

Define Static variables, and their advantages/disadvantages

Answer 14

The variable is bound to storage before execution; efficient but no recursion.

Question 15

Define Stack-dynamic variables, and their advantages/disadvantages

Answer 15

The variable is bound to storage when their declaration statement is reached; supports recursion with overhead.

Question 16

Define Explicit heap-dynamic variables, and their advantages/disadvantages

Answer 16

Explicit heap-dynamic variables are nameless (abstract) memory cells that are
allocated and deallocated by explicit run-time instructions; good for dynamic structures.

Question 17

Define Implicit heap-dynamic variables, and their advantages/disadvantages

Answer 17

The variable is bound to heap storage only when they are assigned a value; flexible but slow and error-prone.

Question 18

Define lifetime, scope, static scope, and dynamic scope.

Answer 18

Lifetime: How long a variable is bound to memory

Scope: The range of statements where the variable is visible.

Static Scope: Determined by the text layout before running.

Dynamic Scope: Determined by the call chain while running.

Question 19

How is a reference to a nonlocal variable in a static-scoped program connected to its definition?

Answer 19

The compiler first searches the local declarations. If not found, it searches the “static parent” (the enclosing program unit), then that parent’s parent, and so on, until the definition is found

Question 20

General problem with static scoping.

Answer 20

It often allows more access to variables than is necessary; structure decays as programs change.

Question 21

What is the referencing environment?

Answer 21

It is the collection of all variables that are visible in that statement.

Question 22

What is a static ancestor of a subprogram? What is a dynamic ancestor?

Answer 22

Static Ancestor: The enclosing subprogram

Dynamic Ancestor: The calling function

Question 23

What is a block?

Answer 23

A code section with its own local scope.

Question 24

What is the purpose of let constructs.

Answer 24

To bind names to values in a small scope.

Question 25

ML let vs C block variables.

Answer 25

ML lets bind immutable values; C variables are mutable.

Question 26

Describe the encapsulation of an F# let inside a function and outside all functions.

Answer 26

Inside a function: The scope extends from the definition to the end of the function (or indentation block). Outside all functions: The name is global, and its scope extends to the end of the file.

Question 27

What are the advantages and disadvantages of dynamic scoping?

Answer 27

Advantages: It is convenient because parameters don't need to be passed explicitly; they are implicitly visible from the caller. Disadvantages: It makes programs hard to read less reliable, and slower

Question 28

Advantages of named constants.

Answer 28

Improves readability and simplifies later modification.