Chapter 5 : Problem Set

Q6 : 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   :

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

b.In sub1: sub1
   In sub2: sub1
   In sub3: sub1.

Q7 : 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();

A    :

Static scope: x=5

Dynamic scope: x=10

Q8 : 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.

A    :

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)

Q9 : 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.

A    :

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

Q10 : 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.

A     :

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