Lecture 5

Question 1

What is the scope of a variable?

Answer 1

The scope of a variable is the range of statements in which the variable is visible.

Question 2

When is a variable visible in a statement?

Answer 2

A variable is visible if it can be referenced in that statement.

Question 3

What are the types of variables based on scope?

Answer 3

Local and non-local variables.

Question 4

What is static scoping?

Answer 4

A method of linking names to non-local variables so that the variable’s scope can be determined before the program runs.

Question 5

Which languages support nested static scopes?

Answer 5

Ada
JavaScript
Common LISP
Scheme
Fortran 2003+
F
Python.

Question 6

Which languages do not support nested static scopes?

Answer 6

C-based languages.

Question 7

How is a reference to a variable found in a static-scoped language?

Answer 7

The search starts in the subprogram where the variable is referenced. If not found, it continues in the subprogram’s static parent.

Question 8

Can hidden variables be accessed in some languages?

Answer 8

Yes, for example, in Ada.

Question 8

What is a hidden variable in static scope?

Answer 8

A variable in an outer scope that is hidden by another variable with the same name in an inner scope.

Question 9

How are variables typically defined in blocks?

Answer 9

As static dynamic variables.

Question 9

What are blocks in programming?

Answer 9

Sections of code with their own local variables whose scope is minimized.

Question 10

Which languages do not allow block scope inside functions?

Answer 10

Java and C#

Question 11

Where must data declarations appear in C89?

Answer 11

At the beginning of the function, except in nested blocks.

Question 12

Which languages allow variable declarations anywhere in the function?

Answer 12

C99, C++, Java, JavaScript, C#.

Question 13

What is a global variable?

Answer 13

A variable defined outside all functions, potentially visible to all functions in the program.

Question 14

How are global variables managed in C and C++?

Answer 14

Through declarations and definitions, with memory allocation only occurring at the definition.

Question 15

What is a drawback of static scoping?

Answer 15

It often allows more access to variables and subprograms than necessary, and software is highly dynamic.

Question 16

What is a merit of dynamic scoping?

Answer 16

Parameters passed from one subprogram to another can be variables defined in the caller, and none of these needs to be explicitly passed.

Question 17

What is the referencing environment of a statement?

Answer 17

The collection of all variables visible to the statement.

Question 18

How is the referencing environment determined in a static scoped language?

Answer 18

By the local scope plus all ancestor scopes.

Question 19

How is the referencing environment determined in a dynamic scoped language?

Answer 19

By the local variables plus variables of all currently active subprograms.

Question 20

What is a named constant?

Answer 20

A variable that is bound to a value only once.

Question 21

Why are named constants useful?

Answer 21

They aid readability and program reliability.

Question 22

Give an example of a named constant in Java.

Answer 22

final int len = 100;