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University of Toronto
Faculty of Applied Science and Engineering
ECE 106S
PROGRAMMING FUNDAMENTALS
Spring 2007
Midterm Test
Examiner: T.S. Abdelrahman, C. Gibson, and A. Goel
Duration: Two Hours
This exam is open textbook and open notes. Use of computing
and/or communicating
devices is NOT permitted.
Do not remove any sheets from this test book. Answer all
questions in the space provided.
No additional sheets are permitted.
Work independently. The value of each part of each question is
indicated. The total value
of all questions is 100.
Write your name and student number in the space below. Do the
same on the top of each
sheet of this exam book.
Name: ___________________________________(Underline last
name)
Student Number: ___________________________________
Q1. __________ Q7. __________
Q2. __________ Q8. __________
Q3. __________ Q9. __________
Q4. __________ Q10. _________
Q5. __________ Q11. _________
TotalQ6. __________ Q12. _________
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Question 1. (7 marks). General.
Answer the following questions either by Yes or No, or by
providing a very briefand direct
answer when indicated.
(a)Yes or No? Suppose that all memory that is allocated using
new is correctly de-allocated usingdelete. Then program memory can
never be exhausted.
(b)Yes or No? A single next instruction in the DDD debugger
allows running a function tocompletion.
(c) Yes or No? The following code ensures that the value ofxp
cannot be modified in main().class X {
int x;
int get() const;};
int main(){
class X *xp;xp->get();
}
(d)Yes or No? An object file (e.g., main.o) can be executed by
changing its name tomain.exe and typing the command ./main.exe at
the Linux command prompt.
(e)What is the name of the software tool you use in the lab to
convert your C++ code into anexecutable program?
(f) Yes or No? One should always use delete to destroy memory
allocated with new beforereturning from a function?
(g)Yes or No? If you do not provide a copy constructor for your
class, a default one will becreated for you.
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Question 2. (12 marks).The Make Utility.
Consider the Makefile below.
1234567891011
1213141516171819
all: difftool testtool
testtool: testtool.c testtool.hgcc -g -Wall testtool.c -o
testtool
difftool: difftool.o diffdata.o recurse.ogcc difftool.o
diffdata.o recurse.o -o difftool lm
difftool.o: difftool.c difftool.h diffdata.h recurse.hgcc -c -g
-Wall difftool.c
recurse.o: recurse.c recurse.hgcc -c -g -Wall recurse.c
diffdata.o: diffdata.c diffdata.hgcc -c -g -Wall diffdata.c
clean:rm *.o difftool
The following table shows several invocations of the Make
utility using the above correctMakefile. For each invocation,
indicate the commands that are executed as a result of the
invocation, in the order in which they are invoked. To simplify
providing an answer, the lines of
the Makefile are numbered as shown above; just indicate the line
number corresponding to acommand in the table provided below. The
invocations ofMakeare in the order shown in thetable.
Assume that the Makefile exists in the same directory as all the
.cc and .h files.
Recall that the touch command simply updates the timestamp of
its argument to the current
time.
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Make Invocation Commands Executed (indicate line number)make
clean
make recurse.o
make difftool
make all
touch difftoolmake
touch diffdata.hmake
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Question 3. (9 marks).Pointers and Memory Management.
Assume that the following code will compile and run
properly.
1 int a = 6;2 int *b = &a;
34 int *5 foo(int **c)6 {7 (**c)++;8 *c = b;9 int *d = new
int;10 *d = 10;11 // Point #112 return d;13 }1415 int16 main()17
{18 int e = 7;19 int *f = &e;2021 f = foo(&f);22 (*f)++;23
// Point #224 return 0;25 }
(a) (3.5 marks). Complete the following diagram by showing the
values of variables and/orpointers when execution reaches the point
labeled Point #1. For an integer variable,
simply show the integer value inside the corresponding box. For
a pointer, indicate the value
of the pointer by drawing an arrow from the box corresponding to
the pointer to the boxcorresponding to the variable the pointer
points to.
fd e
b ca
new int
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(b) (3.5 marks). Complete the following diagram by showing the
values of variables or pointerswhen execution reaches the point
labeled Point #2. For an integer variable, simply show
the integer value inside the corresponding box. For a pointer,
indicate the value of thepointer by drawing an arrow from the box
corresponding to the pointer to the box
corresponding to the variable the pointer points to. Cross out
any variables, pointers or
memory allocations that no longer exist.
fd e
b ca
new int
(c) (2 marks). While the program will run correctly as written,
it contains a non-fatal memoryallocation problem. Write the single
line of code that will fix the error. Specify the line
number in the program after which the line of code should be
inserted.
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Question 4. (8 marks).Scopes.
The following class definition describes a simple C++ class
called sampleClass.
#include using namespace std;
class sampleClass {private:
int val;public:
sampleClass();sampleClass(int v);~sampleClass();
};
sampleClass::sampleClass(){
val = 0;cout
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Consider the following code, which uses sampleClass:
sampleClass a(1);
void f1(){
sampleClass a[2];cout
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In the space provided below, write the output that an execution
of the above program wouldproduce in the order in which it is
produced. Use one entry in the table for each line of output
produced.
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Question 5. (12 marks).Classes and Objects.
Consider the following definitions and partial
implementation.
struct triplet {int first;
int second;int third;
};
class mystery {
private:int x;int y;struct triplet* the_triplet;
public:mystery(int f, int s, int t);~mystery();mystery &
mystery_member(const mystery & other) const;
};
mystery::mystery(int f, int s, int t) {the_triplet = new struct
triplet;the_triplet->first = f;the_triplet->second =
s;the_triplet->third = t;
}
mystery::~mystery() {delete the_triplet;
}
mystery & mystery::mystery_member(const mystery & other)
const {
// This is the mystery
}
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(a) (6 marks).Indicate by placing an X in the appropriate column
whether each of the followingstatements that appear in the body of
a main() function that uses mystery is valid, or notvalidgiven the
definition ofmystery above. A statement is valid if it compiles
and
executes correctly. A statement is not valid if it either
generates a compile-time error, or if itcompiles correctly, but
produces a run-time error (i.e., the programs stops with an error
as
soon as the statement is executed). Assume that each of the
statements is independent of theothers.
Statement Valid Not
Valid
mystery f(1,2,3);
mystery g;
mystery f(1,2,3);cout
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Question 6. (8 marks).Memory Management.
Consider the following definition of the two classes, database
and element.
class database {private:
int count;element** thearray;
public::::
};
class element {private:
int count;char* name;
public:
:::
};
The public functions of each of the two classes include the
constructors, accessor methods and
the destructor.
A main function uses these class definitions to construct a
database object calledmydatabase and many element objects as shown
in the figure below.
0 1 2 3 n-1dynamically allocated array
dynamically
allocated
objects of typeelement
dynamically allocated char arrays
count
thearray
countname
countname
countname
means NULL
mydatabase
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(a) (4 marks). Write the following constructors for the two
classes, database and element.The constructor for element should
initialize count to 0 and name to an empty string. The
constructor for database should initialize count to 0 and
dynamically create an n element
array as shown in the figure above. Each element of the array
should be initialized to NULL.
database::database(int n) {
}
element::element() {
}
(b) (4 marks). Write the destructors of the two classes,
database and element such that nomemory leaks exist when the object
mydatabase goes out of scope. Note that all variables
are dynamically allocated as indicated in the above figure,
except mydatabase, which is an
automatic variable. Write your code in the space provided
below.
database::~database() {
}
element::~element() {
}
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Question 7. (12 marks). Objects.
Study the following class definition and implementation.
struct pair {
int first;int second;
};
class usePair {private:
bool valid;struct pair* thepair;
public:usePair();usePair(int f, int s);~usePair();void
setFirst(int f);void setSecond (int s);usePair & operator=
(usePair rhs);void print();
};
#include "usepair.h"#include "iostream"using namespace std;
usePair::usePair() {valid = true;thepair = new struct
pair;thepair->first = 0;thepair->second = 0;
}
usePair::usePair(int f, int s) {valid = true;thepair = new
struct pair;thepair->first = f;thepair->second = s;
}
usePair::~usePair() {delete thepair;
}
void usePair::setFirst(int f) {thepair->first = f;
}
void usePair::setSecond(int s) {thepair->second = s;
}
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usePair & usePair::operator= (usePair rhs) {valid =
rhs.valid;thepair->first =
rhs.thepair->first;thepair->second =
rhs.thepair->second;rhs.thepair->first =
thepair->second;rhs.thepair->second =
thepair->first;return (*this);
};
void usePair::print() {cout
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Indicate what is being printed by each statement in the above
main function. For simplicity, eachstatement that produces output
has been given a number, and you can write the output of each
statement in the table below.
Statement # Output
1
2
3
4
5
6
7
8
9
10
11
12
Hint: A picture is worth a thousand words.
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Question 8. (9 marks).Linked Lists.
(a) (3 marks). You are given two pointers P and Q to the
singly-linked list shown below.Assume that each node in the list
contains a data field (of type integer) and a next field.
Use the P and Q pointers to switch the positions of the nodes B
and C so that the nodes
occur in the order A, C, B and D. Do not simply swap the integer
values associated withnodes B and C. Also, do not change the values
of P and Q and do not use any additional
variables.
A CB D
P Q
4321
data next
(b) (6 marks). You are again given two pointers P and Q to the
list shown below. Use thesepointers to switch the positions of the
nodes B and E so that the nodes occur in the order A,
E, C, D, B and F. Do not simply swap the integer values
associated with nodes B and E, and
do not change the values of P and Q. You can declare and use one
additional variable.
P Q
A B
1
C D E F
65432
data next
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Question 9. (6 marks).Tree Traversals.
(a) (3 marks). Give the inorder, preorder, and postorder
traversals of the tree shown below. Thetree represents the
mathematical expression x y + z.
+
- z
Inorder Traversal:
Preorder Traversal:
Postorder Traversal:
(b) (3 marks). The following tree is a Binary Search Tree (BST)
that contains all integersbetween 1 and 14. Give the inorder
traversal of the tree.
Inorder Traversal:
x y
10
6
2
1
11
127
13
14
8
93
5
4
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Question 10. (5 marks).Tree Traversals.
Write a recursive function to perform the triple-order traversal
of a binary tree, meaning that for
each node of the tree, the function first visits the node, then
traverses its left subtree (in triple-order), then visits the node
again, then traverses its right subtree (in triple-order), then
visits the
node again. Hence, the triple-order traversal of the tree shown
below is:
3 4 2 2 2 4 1 1 1 4 3 5 5 5 3.
12
4 5
3
Write a recursive function to perform the triple-order traversal
of a binary tree. Assume that
visiting a node simply prints its key tocout. Your code should
be very short (5-6 lines)!Excessively long code will be
penalized.
You may assume the following declarations:
class treenode {public:
int data;
treenode *left;treenode *right;};treenode *Root; // root of the
tree
void tripleorder (treenode *rt) {
}// This is how tripleorder is calledtripleorder(Root);
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Question 11. (6 marks).C++ I/O.
Your task is to expand the command parser from Lab 3 to
implement an additional operation,printmultiple, which accepts
multiple student numbers and prints out a record for eachstudent.
The command format is:
printmultiple N stnum1 stnum2 ... stnumN
The first parameter, N, indicates the number of student numbers
that follow on the line. The
following examples are both valid commands:
printmultiple 0Done.
printmultiple 2 987654321 987654320OUTPUT FOR STUDENT 987654321
APPEARS HERE
OUTPUT FOR STUDENT 987654320 APPEARS HERE
Done.
If any of the numbers are invalid (e.g., foo or -12), you should
skip processing theremainder of the line without printing an error
message. You may assume that you have
access to the following function, which handles the printing of
the student record:
bool printStudent (int stnum);
The printStudent function will return a false value if the
student number does not exist in
the database; in this event, you should skip the remaining
student numbers, without printing
an error message. When you are finished processing the
printmultiple command (whether
there were errors or not) you should print Done. You are not
expected to handle any other
errors, or produce any additional output.
Using only the cin operator for input, complete the following
code fragment for processing a
single printmultiple command:
char buffer[MAX_COMMAND_SIZE];
// ...
if (!strcmp(buffer, printmultiple)) {
}
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Question 12. (6 marks).Recursion.
A tail-recursive function is a special kind of recursive
function in which after completing all
other operations, the function simply calls itself and returns
the result of this call. Below, thefactorial function is shown on
the left. Write a tail-recursive factorial function. A template
for
this function is shown on the right.
Original function Tail-recursive function
intfactorial(int n){
if (n
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