Chapter 5 Answers

Nama : Christian Gunawan
NIM : 1801384174

Kali ini saya akan menjawab assigntment #5 dari chapter 5 Programming Language Concepts R Sebesta E-book :

Review Questions#6-10 :

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

L-value is the address of a variable , because the address is what is required when the name of a variable appears in the left side of an assignment.

R-value is a name for a variable's value because it is what is required when the name of the variable appears in the right side of an assignment statement

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.

Whilst the time at which a binding takes place is called binding time.

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

Language design time — bind operator symbols to operations
Language implementation time– bind floating point type to a representation
Compile time — bind a variable to a type in C or Java
Load time — bind a C or C++ static variable to a memory cell)
Runtime — bind a non-static local variable to a memory cell

9. Define static binding and dynamic binding.

A static binding is if it first occurs before run time and remains unchanged throughout program execution. A dynamic binding is if it first occurs during execution or can change during execution of the program.

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

Disadvantage : A static binding is if it first occurs before run time and remains unchanged throughout program execution. A dynamic binding is if it first occurs during execution or can change during execution of the program.

Advantage : There are several different bases for implicit variable type bindings. The simplest of these is naming conventions. In this case, the compiler or interpreter binds a variable to a type based on the syntactic form of the variable’s name.

Problem Set #6-10 : 

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 declaration
of x is the correct one for a reference to x?
i. sub1
ii. sub2
iii. sub3
b. Repeat part a, but assume dynamic scoping.

a. In sub1: sub1
    In sub2: sub1
    In sub3: main

b.In sub1: sub1
   In sub2: sub1
   In 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 scoping: x=5;
Dynamic scoping: 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, assuming

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, assuming

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 */

. . . 1

while (. . .) {

int c, d, e; /* definition 3 */

. . . 2

}

. . . 3

}

. . . 4

}

For each of the four marked points in this function, list each visible variable,

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