CSC3403 Comparative Programming Languages

06 Jun

CSC3403 – Comparative Programming Languages Semester 1, 2012 Page 1
Question 1 46 marks
Please keep your answers short. There is no need for complete sentences
— use phrases or list key points where possible.
Part marks may be awarded.
(1) (
1 mark) Name or describe an abstraction feature of a programming
(2) (
1 mark) Name two (2) languages with statement syntax that is very
similar to that of the C language.
(3) (
1 mark) Name a language feature whose use can enhance the reliability of programs written in that language.
(4) (
1 mark) Why is readability of a programming language important?
(5) (
1 mark) What are the three extra constructions present in Extended
BNF (EBNF) compared to BNF?
(6) (
1 mark) List the tokens in the the following C statement:
(7) (2 marks) Write a single EBNF rule for the language defined by the
following syntax graph.


(8) (2 marks) Describe in English language the sentences produced by the
following grammar.
S aSb | aXb
y | z
(9) (3 marks) Given the grammar
decl declist | ǫ
decl type varlist ;
type int | float | char
varlist ident , varlist | ident
a | b | x | y
Produce a leftmost derivation for the following sentence of the langage:
int x,y; char a;
CSC3403 – Comparative Programming Languages Semester 1, 2012 Page 2
(10) (1 mark) How can a grammar be proven to be ambiguous?
(11) (
1 mark) What form of grammar rule is required to produce right
in expressions?
(12) (
1 mark) What derivation order does a LR parser employ in parsing
a sentence of a language?
(13) (
2 marks) What is the lifetime of
(a) a stack-dynamic variable
(b) an explicit dynamic variable
(14) (
1 mark) What is a type error?
(15) (
1 mark) What is meant by strong typing?
(16) (
1 mark) What kind of programming error can arise when implicit
variable declarations
are permitted in a language?
(17) (
1 mark) What is meant by the scope of an identifier?
(18) (
2 marks) The “lost variable” problem when using heap dynamic variables leads to a so-called “memory leak”. Describe a situation that
demonstrates this problem.
(19) (
2 marks) Consider the array x: array [0..10, 20..30] of double
If a double occupies 8 bytes, and access is in row major order, what is
the byte offset (the number of bytes from the beginning of the array,
starting from zero) of the element
(20) (
1 mark) What is short circuit expression evaluation? Give an example
of a C expression which can be evaluated in this way.
(21) (
1 mark) What is the minimum number of loop iterations possible for
a pre-tested loop?
(22) (
2 marks) Ada and Modula-2 use explicit end of statement keywords
and sequences of statements, like this:
ifStmt if expr then stmtList else stmtList end
C and Pascal use blocks and no statement terminating keyword, like
this (using Pascal syntax):
ifStmt if expr then block else block
stmt | begin stmtList end
Give one advantage for using each of these two approaches.

CSC3403 – Comparative Programming Languages Semester 1, 2012 Page 3
(23) (1 mark) What is the dynamic parent of a subprogram?
(24) (
3 marks) Consider the following program, written in a C-like language.
int x;
void f(int a) {a = a+2; x = x+1;}
void main() {
x = 1;
What value of x will be printed by the main program under each of the
following conditions? Imagine that formal parameter
a of function f is
being passed:
i. by
ii. by value-result
iii. by reference
(25) (2 marks) What parameter passing mode (in, in-out or out) do the
following parameter passing mechanisms implement?
(26) (
1 mark) Why are the return address and parameters placed in a
procedure’s activation record
before its local variables?

CSC3403 – Comparative Programming Languages Semester 1, 2012 Page 4
(27) (2 marks) Consider the following skeletal program, written in a language with static scope.
procedure Main;
procedure A;
procedure B;
procedure C;
{ C }
end { C }
begin { B }
end { B }
procedure D;
procedure E;
{ E }
end { E }
begin { D }
end { D }
begin { A }
end { A }
begin { Main }
end { Main }
Imagine that the following procedure calls have taken place:
Main calls A
A calls D
D calls E
E calls B
B calls C
i. Draw the run time stack showing just activation record instances
and static links at the time when C is executing.
Do not show
contents of each activation record instance, apart from the static
ii. List the names of procedures that can be called from procedure B.
(28) (
1 mark) Give two ways in which overloaded subprograms of the same
name must differ from each other in order to be valid definitions.
(29) (
1 mark) What are the two key features of an Abstract Data Type?
(30) (
1 mark) Give one advantage of using an abstract data type.
(31) (
1 mark) What is an exception?
(32) (
1 mark) What is the advantage of using language defined exception
features to deal with exceptions rather than using standard
techniques such as calling an error procedure?

CSC3403 – Comparative Programming Languages Semester 1, 2012 Page 5
(33) (1 mark) What are the two key features of an Object Oriented language, beyond those provided by an Abstract Data Type?
(34) (
1 mark) Describe one significant design decision faced by designers
of object oriented languages?

CSC3403 – Comparative Programming Languages Semester 1, 2012 Page 6

Question 2 11 marks
In this question you are required to write a number of small Haskell functions.
You may use any Standard Prelude function in writing these functions. If
you need, you may write other functions in order to implement the functions
specified below; if you do so, be sure to show their definitions.
One of the definitions use the Maybe data type. Recall that the Maybe type
has definition:
data Maybe a = Nothing | Just a
(1) (4 marks) Write the function

cap :: String -> String.
The application
cap str will replace the initial letter of each word in str
with a capital letter. Assume that str contains words separated by one
or more space characters (you
do not need to consider other whitespace
such as tabs and newlines). For example:
cap “zip” “Zip”
cap ” aaa bbb ccc”
” Aaa Bbb Ccc”
Hint: Use the toUpper function from the Char module to help in
writing this function.
(2) (
3 marks) Assume the definition:
data Tree x = Node x (Tree x) (Tree x) | Nil.
Write the function
lookT :: Ord a => a -> Tree (a,b) -> Maybe b that searches a
binary tree of (key,value) pairs. The values are stored in sorted order:
for each node, the left subtree contains only nodes with keys less than
the node’s key, while the right subtree contains only nodes with keys
greater than the node’s key.
lookT key tree searches tree and returns the
value associated with
key, if a matching key value is found. Otherwise
it returns
Nothing. The function should only search in sub-trees likely
to contain
key. For example:
lookT 1 (Node (1,”Fred”) Nil Nil Just “Fred”
lookT 1 (Node (2,”Mary”) Nil Nil
lookT 1 (Node (2,”Mary”) (Node (1,”Fred”) Nil Nil) Nil)
Just “Fred”
(3) (4 marks) Write the function
mrep :: [String] -> String -> String.
mrep xs str returns str, where successive occurrences of the ’$’ character in str are replaced by successive elements in xs. The length of xs
does not need to match the number of ’$’. For example:

mrep [“aa”,”bb”] “xx $ yy $ zz” “xx aa yy bb zz”
mrep [“aa”] “xx $ yy $ zz” “xx aa yy $ zz”
mrep [“aa”,”bb”] “xx $ yy” “xx aa yy” …/7

CSC3403 – Comparative Programming Languages Semester 1, 2012 Page 7

Question 3 9 marks
In this question you are required to write a number of Prolog relations. You
may need to define other relations in order to answer the questions below.
(1) (3 marks) Define the relation maxList(L,N) such that N is the maxi
mum value that appears in the (non-empty) list L. For example:

?- maxList([1,10,5,7], X). X = 10 .
(2) Assume the presence of a database of family relations:
parent(X,Y) asserts that X is a parent of Y, and
husband(H,W) asserts that H is the husband of W.
i. (
2 marks) Write the relation spouse(X,Y) that is true whenever
X is married to Y.
ii. (
2 marks) Write the relation inlaw(X,Y) that is true whenever Y
is a parent-in-law of X. (A person’s parents-in-law are that person’s
spouse’s parents.)
iii. (
2 marks) Write the relation sibinlaw(X,Y) that is true whenever Y is a brother-in-law or a sister-in-law of X. (A person’s sistersin-law are that person’s spouse’s sisters; similarly for brothers-inlaw.)
End of examination

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