Chapter 5 Programming Language Concepts R Sebesta

Nama: Stefanus Eduard Adrian
NIM: 1801382963

Kali ini saya akan menjawab Assignment #5 dari Chapter 5 Programming Language Concepts R Sebesta

Review Questions

6. What is the l-value of a variable? What is the r-value?

*The l-value of a variable is the address of that variable. An l-value represents a storage region's "locator" value.

The r-value of a variable is the data (value) of that variable. All l-values are r-values but not all r-values are l-values.

7. Define binding and binding time.

* A binding is an association between an attribute and an entity, such as between a variable and its type or value, or between an operation and a symbol.

Binding time is the time at which a binding takes place.

8. After language design and implementation [what are the four times bindings can take place in a program?]

*-compile time (bind a variable to a type in C or Java)

-link time

-load time (bind a C or C++ static variable to a memory cell)

-run time (bind a nonstatic local variable to a memory cell)

9. Define static binding and dynamic binding.

*Static binding is a binding which occurs before run time and remains unchanged throughout program execution.

Dynamic binding is a binding which occurs during execution or can change during execution of the program.

10. What are the advantages and disadvantages of implicit declarations?

*Advantages:

-Can make it easier for the programmer to write code, since he/she doesn’t have to also write the declarations

-Maintainability can be easier too, since the information about a variable’s type is not written down in a part of the program distant from where the variable is used

-Readability can be better since a reader can probably infer the variable’s name or its context

Disadvantage:

-Reliability will probably suffer since the programmer may not always realize the type that the compiler assigned a variable

Problem Set

6. Consider the following JavaScript skeletal program:

// The main program var x;

function sub1() {

  var x;

  function sub2() {

    . . .

  }

}

function sub3() {

  . . . 

}    Assume that the execution of this program is in the following unit order:

main calls sub1

sub1 calls sub2

sub2 calls sub3

a. Assuming static scoping, in the following, which dec- laration of x is the correct one for a reference to x?

 i. sub1: sub1

ii. sub2: sub1

iii. sub3: main

b. Repeat part a, but assume dynamic scoping.

i. sub1: sub1

ii. sub2: sub1

iii. sub3: sub1

7. Assume the following JavaScript program was interpreted using static-scoping rules. What value of x is displayed in function sub1? Under dynamic-scoping rules, what value of x is displayed in function sub1?

var x; function sub1() {

  document.write("x = " + x + "<br />");

}

function sub2() {

  var x;

  x = 10;

  sub1();

}

x = 5;

sub2();

*Static scope: x=5

Dynamic scope: x=10

8. Consider the following JavaScript program:

var x, y, z; function sub1() {

  var a, y, z;

  function sub2() {

    var a, b, z;

    . . .

  }

  . . .

}

function sub3() {

  var a, x, w;

  . . .

}

List all the variables, along with the program units where they are declared, that are visible in the bodies of sub1, sub2, and sub3, assum- ing static scoping is used.

*sub1: a(sub1) y(sub1) z(sub1) x(main) 
sub2: a(sub2) b(sub2) z(sub2) y(sub1) x(main) 
sub3: a(sub3) x(sub3) w(sub3) y(main) z(main)

9. Consider the following Python program:

x = 1; y = 3;

z = 5;

def sub1():

  a = 7;

  y = 9;

  z = 11;

  . . .

def sub2():

  global x;

  a = 13;

  x = 15;

  w = 17;

  . . .

  def sub3():

    nonlocal a;

    a = 19;

    b = 21;

    z = 23;

    . . .

. . .

List all the variables, along with the program units where they are declared, that are visible in the bodies of sub1, sub2, and sub3, assum- ing static scoping is used.

* Variable           Where Declared

In sub1:

a                     sub1

y                     sub1

z                     sub1

x                     main

In sub2:

a                     sub2

x                     sub2

w                    sub2

y                     main

z                     main

In sub3:

a                     sub3

b                     sub3

z                     sub3

w                    sub2

x                     sub2

y                     main

10. Consider the following C program:

void fun(void) {  int a, b, c; /* definition 1 */

  . . .

  while (. . .) {

    int b, c, d; /*definition 2 */   

. . .  à1

    while (. . .) {

int c, d, e; /* definition 3 */   

 . . . à 2

     }  

 . . .  -à3

    } 

. . .  à4

}

For each of the four marked points in this function, list each visible vari- able, along with the number of the definition statement that defines it.

* Point 1: a:1 b:2 c:2 d:2

Point 2: a:1 b:2 c:3 d:3 e:3

Point 3: a:1 b:2 c:2 d:2

Point 4: a:1 b:1 c:1