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{Spring 1985\hfil Comp 190:  {\it Programming Languages}\hfil190-11.\folio}
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\centerline{Final Exam}
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\centerline{9:00 {\sevenrm AM} -- 12:00 Noon, May 1, 1985}
\bigskip\noindent
Problem 1.  (18 points)
\par
For each of the following six programming languages,
Ada, BASIC, COBOL, FORTRAN, LOGO, and Pascal,
characterize those application areas which are especially well-suited for that
language.
Mention specific features of the language to justify your claims.
(About three sentences per language, please.)
\medskip\noindent
Problem 2.  (12 points)
\par
Consider the following Pascal program:
\medskip
\begingroup
 \obeylines\obeyspaces\tt
program M ;
\ \ \ var A: array[1..2] of integer ;
\ \ \ procedure P(Y, Z: integer) ;
\ \ \ \ \ \ var X: integer ;
\ \ \ \ \ \ procedure Q(var X: integer) ;
\ \ \ \ \ \ \ \ \ begin (*{\it body of Q}\ *)
\ \ \ \ \ \ \ \ \ \ \ \ X := X - A[1] ;
\ \ \ \ \ \ \ \ \ \ \ \ P(X, X)
\ \ \ \ \ \ \ \ \ end (*{\it body of Q}\ *);
\ \ \ \ \ \ begin (*{\it body of P}\ *)
\ \ \ \ \ \ \ \ \ Z := Y div Z
\ \ \ \ \ \ \ \ \ Q(A[A[2]]) ;
\ \ \ \ \ \ end (*{\it body of P}\ *);
\ \ \ begin (*{\it body of M}\ *)
\ \ \ \ \ \ A[1] := 2 ;
\ \ \ \ \ \ A[2] := 1 ;
\ \ \ \ \ \ P(A[1], A[2])
\ \ \ end (*{\it body of M}\ *) .
\endgroup
\medskip\noindent
If you execute this program, it should (in four or fewer procedure calls)
``bomb'' when it tries to divide an integer by zero.
Draw the stack and display at the moment when the program bombs.
Be sure to show on the stack all variables, parameters,
and dynamic and static environment chains.
\medskip\noindent
Problem 3.  (10 points)
\par
Assume you have a programming language with four operators,
%emacs-mathOK
$\clubsuit$, $\diamondsuit$, $\heartsuit$, and $\spadesuit$,
with left-to-right associativity and the following operator precedence rules:
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{\settabs\+\indent&Highest precedence\qquad&\cr
\+&Highest precedence&$\clubsuit$\cr
\+&Middle precedence&$\diamondsuit\quad\heartsuit$\cr
\+&Lowest precedence&$\spadesuit$\cr}
\smallskip\noindent
Show both the tree form (Fig. 6-2, page 153) and postfix notation for
the expression:
$$(a\ \diamondsuit\ b\ \spadesuit\ c)
\ \heartsuit\ d\ \clubsuit\ e\ \diamondsuit\ (f \clubsuit g)$$
\vfil\eject\noindent
Problem 4.  (10 points)
\par
An Ada package has two parts, for example:
\medskip
\begingroup
 \obeylines\obeyspaces\tt
package INT\_STACK\_TYPE is
\quad\dots
end INT\_STACK\_TYPE
package body INT\_STACK\_TYPE is
\quad\dots
end INT\_STACK\_TYPE
\endgroup\medskip\noindent
What is the purpose of each of these two parts?
Which part(s) must be looked at by (a) someone using the package, and
(b) someone modifying the package?
\medskip\noindent
Problem 5.  (7 points)
\par
Draw the state of a LOGO interpreter using a reference count
garbage collector after it executes each of the following
four statements.
\medskip
\begingroup
 \obeylines\obeyspaces\tt
MAKE "L1 [5 6]
MAKE "L2 (BUTFIRST :L1)
MAKE "L1 (FPUT 4 :L2)
MAKE "L2 (BUTFIRST :L1)
\endgroup
\medskip\noindent
Problem 6. (6 points)
\par
Consider the following program written in a generic language:
\medskip
\begingroup
 \obeylines\obeyspaces\tt
program foo ;
\ \ \ var n: integer ;
\ \ \ function g(): integer;
\ \ \ \ \ \ begin
\ \ \ \ \ \ \ \ \ return( n+1 )
\ \ \ \ \ \ end ;
\ \ \ function f(): integer;
\ \ \ \ \ \ var n: integer ;
\ \ \ \ \ \ begin
\ \ \ \ \ \ \ \ \ n := 1 ;
\ \ \ \ \ \ \ \ \ return( g() )
\ \ \ \ \ \ end ;
\ \ \ begin
\ \ \ \ \ \ n := 5 ;
\ \ \ \ \ \ print( f() )
\ \ \ end ;
\endgroup
\medskip\noindent
What is the result of executing this program using both (a) dynamic and
(b) static scope rules?  Explain your answer.
\medskip\noindent
Problem 7.  (6 points)
\par
Give at least two good reasons why you can't write a general-purpose
quicksort routine in Pascal.
\vfil\eject\noindent
Problem 8.  (6 points)
\par
Assume that {\tt x}, {\tt y}, and {\tt z} have been declared to
be integer variables in Ada and that {\tt x} and {\tt y} are both positive.
Write two or three lines of Ada that will set the integer variable {\tt z} to
the minimum of 1000000000 and {\tt x+y}.
Use Ada's exception-handling mechanism to make sure that your code
works correctly even if the computation of {\tt x+y} signals the
Ada exception {\tt OVERFLOW}.
\medskip\noindent
Problem 9.  (5 points)
\par
Make a movie showing
the stack of temporary values of a compiled Pascal program executing
the expression {\tt x+(y*z)-(x mod z)} when {\tt x} is 5,
{\tt y} is 6, and {\tt is 7}.
\medskip\noindent
Problem 10.  (5 points)
\par
Write a Pascal procedure {\tt increment2} which takes two integer
parameters.
The effect of {\tt increment2} is to make each actual parameter one greater
than it was before the call.
For example:
\medskip
\begingroup
 \obeylines\obeyspaces\tt
increment2(A[i], A[j]) ;
\endgroup\medskip\noindent
is equivalent to:
\medskip
\begingroup
 \obeylines\obeyspaces\tt
A[i] := A[i] + 1 ;
A[j] := A[j] + 1 ;
\endgroup\medskip\noindent
if {\tt i} and {\tt j} are different and is equivalent to:
\medskip
\begingroup
 \obeylines\obeyspaces\tt
A[i] := A[i] + 1 ;
\endgroup\medskip\noindent
if {\tt i} and {\tt j} are the same.
\medskip\noindent
Problem 11.  (5 points)
\par
Pascal prohibits programmers from directly using the value returned
by a pointer-valued function as a pointer reference.
For example, you cannot use {\tt f(5)\char'136} in a Pascal expression,
even if {\tt f} is function that maps integers into pointers.
Can you think of any justification for this restriction?
Explain your reasoning.
Do you anticipate any problem in implementing an extension of Pascal
which does not have this restriction?
\medskip\noindent
Problem 12.  (5 points)
\par
It is generally thought that FORTRAN programs are more efficient
than Pascal programs; however, it is quite likely that, if you take
a Pascal program and translate it into FORTRAN in a straightforward
manner (assume the Pascal program had no recursion), the FORTRAN
program will use more storage.
Discuss briefly (one paragraph) why this is so.  
\medskip\noindent
Problem 13.  (5 points)
\par
Write FORTRAN {\tt READ} and {\tt FORMAT} statements to input
80 one-digit numbers, typed one per column on a card, into an
integer array {\tt C}.
\medskip\noindent
\bye