Princess Nora Bint Abdul Rahman University
College of Computer and Information Sciences
Department of Computer Science
1434 - 1435 (Second semester)
CS 444 - Programming Languages Concepts
Assignment 2
Due date: Thursday 3/4/2014 (8 am - 1:30 pm)

Question 1. Consider the following skeletal C program:
void fun1(void); /* prototype */
void fun2(void); /* prototype */
void fun3(void); /* prototype */
void main() {
int a, b, c;
. . .
}
void fun1(void) {
int b, c, d;
. . .
}
void fun2(void) {
int c, d, e;
. . .
}
void fun3(void) {
int d, e, f;
. . .
}
Given the following calling sequences and assuming that dynamic scoping is used,
what variables are visible in each function after the execution of the last called
function? Include with each visible variable the name of the function in which it was
defined.
a. main calls fun1; fun1 calls fun2; fun2 calls fun3.
b. main calls fun2; fun2 calls fun3; fun3 calls fun1.
CS 444
Assignment 2
Solution:
a. main calls fun1; fun1 calls fun2; fun2 calls fun3.
d, e, f
fun3
c
fun2 (d and e of fun2 are hidden)
b
fun1 (c and d of fun1 are hidden)
a
main (b and c of main are hidden)
b. main calls fun2; fun2 calls fun3; fun3 calls fun1.
b, c, d
fun1
e, f
fun3 (d of fun3 is hidden)
a
main (b and c of main are hidden)
(c, d and e of fun2 are hidden)
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CS 444

Assignment 2
Question 2. Consider the following JavaScript program:
var x, y, z;
function sub1() {
var a, y, z;
function sub2() {
var a, b, z;
. . .
1
}
. . .
2
}
function sub3() {
var a, x, w;
. . .
3
}
List all the variables, along with the program units where they are declared, that are
visible in the bodies of sub1, sub2, and sub3, (Points 1, 2, and 3) assuming static
scoping is used.
Solution:
Point 1 - In sub2:
a, b, z in sub2.
y in sub1 (a and z of sub1 are hidden).
x the global variable (global variables y and z are hidden).
Point 2 - In sub1:
a, y, z in sub1.
x the global variable (global variables y and z are hidden).
Point 3 - In sub3:
a, x, w in sub3.
y, z the global variables (global variable x is hidden).
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CS 444

Assignment 2
Question 3. Assume the following JavaScript program was interpreted using staticscoping 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();
Solution:
Static scoping: x is 5
Dynamic scoping: x is 10
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CS 444

Assignment 2
Question 4. Given the following grammar:
1. S  A B
2. A A a | a
3. BB b | b
Parse the sentence a a a b b using Shift-reduce parsing in the form of the table
below.
Stack
Input Sequence
Action
Stack
Input Sequence
Action
()
aaabb
-
(a)
aabb
Shift a
(A)
aabb
Reduce (2)
(A a)
abb
Shift a
(A)
abb
Reduce (2)
(A a)
bb
Shift a
(A)
bb
Reduce (2)
(A b)
b
Shift b
(A B)
b
Reduce (3)
(A B b)
-
Shift b
(A B)
-
Reduce (3)
(S)
-
Accept/Success (1)
Solution:
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CS 444

Assignment 2
Question 5. Given the following grammar:
1.
2.
3.
4.
SaB
B““
BA
AbB
And the following parsing table:
S
A
B
a
1
-
b
4
3
$
2
Parse the sentence a b b using LL(1) Parser in the form of the table below.
Hint: Rule 2 means that you will add nothing instead of B.
Stack
Input
Action
Output stream
Stack
Input
Action
Output stream
[S, $]
abb$
-
-
[a, B, $]
abb$
Rewrite S by rule 1
[1]
[B, $]
bb$
Remove a and a
(matching)
[1]
[A, $]
bb$
Rewrite B by rule 3
[1, 3]
[b, B, $]
bb$
Rewrite A by rule 4
[1, 3, 4]
[B, $]
b$
Remove b and b
(matching)
[1, 3, 4]
[A, $]
b$
Rewrite B by rule 3
[1, 3, 4, 3]
[b, B, $]
b$
Rewrite A by rule 4
[1, 3, 4, 3, 4]
[B, $]
$
[$]
$
Solution:
Remove b and b
(matching)
Rewrite B and
Accept by rule 2
[1, 3, 4, 3, 4]
[1, 3, 4, 3, 4, 2]
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