CS32 Midterm Exam E01, F15, Phill Conrad, UC Santa Barbara Wednesday, 10/28/2015, 11am 12:15pm

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1 1 CS32 Midterm Exam E01, F15, Phill Conrad, UC Santa Barbara Wednesday, 10/28/2015, 11am 12:15pm Please write your name above AND AT THE TOP OF EVERY PAGE Be sure you turn in every page of this exam. "End of Exam" should appear on the last page. This exam is closed book, closed notes, closed mouth, cell phone off Permitted notes sheet: one sheet of paper (max size 8.5x11") Notes sheets will be collected with the exam, and will not be returned Please write your name on your notes sheet 1. For each part of this question, please write a full unix command (exactly what you would enter at the unix shell prompt) that perfoms the action indicated, in the context indicated. For full credit, the entire command should be entered, not just the "name" of the command. a. (2 pts) Assume that the home directory of user jsmithcontains a subdirectory called cs32, which in turn contains a subdirectory called lab02. Copy every file from that lab02subdirectory that ends in.cppinto the current directory. b. (2 pts) Write a unix command that displays the full path (not the contents) of the current working directory. c. (2 pts) Write a unix command that will cause the current working directory to become the home directory of the current user d. (2 pts) Suppose the current working directory is the lab02subdirectory of some directory that we do not know the name of it might be cs32, but it could be anything (e.g. cs24or cs16). This parent direcctory also contains a lab01subdirectory. Write the unix command that copies every file and every subdirectory of that lab01directory into the current working directory (which, as a reminder, is named lab02) e. (2 pts) Change the permission modes of the directory jsmith(located in the current working directory) so that when ls -ld jsmithis typed, you'll see the following string as the permission modes: drwx--x--x f. (2 pts) Write a command that will list the contents of the current directory in long form, i.e. showing their permission bits, and including hidden files.

2 2 2. The output shown in the box at right illustrates the progress of a particular sorting algorithm that runs in time O(n 2 ), working on the input array: int a[5]={20,50,15,30,12; a. (4 pts) Which sorting algorithm is this? Circle one: bubble sort insertion sort selection sort b. (10 pts) Here is some code for this algorithm. There are two lines where there is code missing, indicated clearly by solid blank lines, and comments FILL IN BLANK HERE. Fill in both blanks so that the algorithm runs correctly. #include <iostream> using namespace std; void printarray(int *a, int n) { for (int i=0; i<n; i++) { cout << a[i] << " "; cout << endl; void swap(int &x, int &y) { int temp=x; x=y; y=temp; int indexofmax(int *a, int n) { int im=0; for (int i=1; i<n; i++) { if (a[i]>a[im]) { // (a) FILL IN BLANK HERE return im; void onestep(int *a, int n) { int im=indexofmax(a,n); swap(,a[im]); int main() { int a[5]={20,50,15,30,12; printarray(a,5); for (int i=5; i>1; i--) { onestep(a,i); printarray(a,5); // (b) FILL IN BLANK HERE

3 3 3. The output shown in the box at right illustrates the progress of yet another sorting algorithm that runs in time O(n 2 ), working on the input array: int a[5]={20,50,15,30,12; a. (4 pts) Which sorting algorithm is this? Circle one: bubble sort insertion sort selection sort b. (10 pts) Here is some code for this algorithm. There are two lines where there is code missing, indicated clearly by solid blank lines, and comments FILL IN BLANK HERE. Fill in both blanks so that the algorithm runs correctly. #include <iostream> using namespace std; void printarray(int *a, int n) { for (int i=0; i<n; i++) { cout << a[i] << " "; cout << endl; void swap(int &x, int &y) { int temp=x; x=y; y=temp; void onestep(int *a, int n) { for (int i=0; ; i++) { // FILL IN BLANK HERE if (a[i] > a[i+1]) { // FILL IN BLANK HERE int main() { int a[5]={20,50,15,30,12; printarray(a,5); for (int i=5; i>1; i--) { onestep(a,i); printarray(a,5);

4 4 4. Finally, the output shown in the box at right illustrates the progress of one more sorting algorithm that runs in time O(n 2 ), working on the input array: int a[5]={20,50,15,30,12; a. (4 pts) Which sorting algorithm is this? Circle one: bubble sort insertion sort selection sort b. (10 pts) Here is some code for this algorithm. There are two lines where there is code missing, indicated clearly by solid blank lines, and comments FILL IN BLANK HERE. Fill in both blanks so that the algorithm runs correctly. #include <iostream> using namespace std; void printarray(int *a, int n) { for (int i=0; i<n; i++) { cout << a[i] << " "; cout << endl; int addtosortedarray(int *b, int size, int x) { // find where to put it int where=0; while ( && b[where]<x) { // FILL IN BLANK HERE where++; // scoot things over for (int i=size; i>where; i--) { b[i] = b[i-1]; // stick it in and return new size // FILL IN BLANK HERE return size+1; int main() { int a[5]={20,50,15,30,12; int b[5]; int size=0; for (int i=0; i<5; i++) { size=addtosortedarray(b,size,a[i]); printarray(b,size);

5 5 5. For this question, and several others that follow, please refer to the code on the handout for the HashTable class. On that handout, you'll find a C++ class that implements a HashTable. The hash function used appears on line 17 of the rightmost column of that handout. As you may recall, we studied two ways of "resolving collisions" in a hash table implementation. This class uses the "linked list" technique. I'll ask about the other technique later on this exam, but for now, focus on the linked list method. In the leftmost column, a class declaration for class HashTable In the center column, code for a main.cpp file that demonstrates, in part, how the constructor, insert, and lookup functions can be used. In the right column, output from that main program. The remaining questions on the exam may make reference to these columns, so familiarize yourself with them briefly before continuing. a. (4 pts) The leftmost column, for hashtable.h, has this on lines 1 and 2: #ifndef _HASH_TABLE_H_ #define _HASH_TABLE_H_ and this on line 33: #endif. Briefly, but precisely explain: what is the purpose of these lines? b. (4 pts) Line 27 of hashtable.h, has this: ~HashTable(); Briefly, but precisely explain: what is this line of code, and what is its role in the class declaration?

6 6 6. For this question, and several others that follow, please refer to the code on the handout for the HashTable class. And, for this problem, we also have an excerpt from hashtable.cppin the box on the right hand side, below. Line 4 has been left out. HashTable::HashTable() { // 1 table = new Node *[SIZE]; // 2 for (int i=0; i<size; i++) { // 3 // 4 // 5 // 6 a. (2 pts) In the center column, in the code for main.cpp, line 27 shows this: HashTable h; Where will the storage for variable hend up? Circle one: heap stack b. (4 pts) Refer to line 15 of hashtable.h, left most column of the handout. Consider this line of code in the context of the code in the box at upper right, showing the default constructor, as it would appear in hashtable.cpp. Then, explain as clearly and precisely as you can, but briefly, why line 15 of hashtable.h has a double star, i.e. Node **table; c. (5 pts) Refer to lines 1-5 of the output of./main in the right most column of the handout. These show what the state of the hash table should be after the default constructor has finished executing, i.e. an empty hash table. Then refer to line // 4 of the code except at upper right, i.e. the line that is omitted. Which of the following, if entered in that blank, correctly completes the code? Circle one. table[i]=null; *(table[i])=null; table[i]->next=null; &(table[i])=null;

7 7 7. (5 pts) For this question please refer to the code on the handout for the HashTable class. And, for this problem, we also have yet another excerpt from hashtable.cppon the reverse side, page 2 of the handout. Again a line near the bottom has been left out. The code on page 2 of the handout shows two function definitions. The second one, insert, has one line of code missing at line 32. What line of code should go there to complete the insertfunction so that it operates correctly? Circle exactly one of the following options. (Note: only one answer is correct, and there is no partial credit.) Circle one: table[i]=p; table[i]=trailp; trailp->next = p; table[i]->next=p table[i]->next=trailp; p->next = trailp; 8. The C++ code for the hash table class on this exam used the "linked list" approach to resolving collisions. a. (4 pts) In the context of hash tables, what does it mean to resolve a collision? Explain precisely and clearly, but briefly. b. (4 pts) Briefly, but precisely and with clarity: what is the other main way we can "resolve collisions" in a hash table implementation?

8 8 9. We have discussed the idea of an Abstract Data Type (i.e. ADT). a. (2 pts) Would the description of a HashTable ADT include the decision to use the "linked list" approach to collision resolution vs. the "other" approach? Circle one: Yes, it would. No, it would not. b. (4 pts) Now briefly explain your answer to the preceding "yes/no" question. (You earn the yes/no points if your answer is correct, regardless of your explanation. You earn these point IF AND ONLY IF both your yes/no answer AND your explanation are BOTH correct.) 10. Briefly distinguish between the idea of a class and instances of a class, using specific examples, in two ways: a. (4 pts) Using an example that refers to objects from everyday life, such as people or books b. (4 pts) Using specific examples from C++ code. That is, actually write some real C++ code, or code excerpts, and show in the code what is a "class" and what is an "instance" of the class. End of Exam total points=100