Midterm Exam #2 Spring (1:00-3:00pm, Friday, March 15)

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1 Print Your Name: Signature: USC address: CSCI 101L Fundamentals of Computer Programming Midterm Exam #2 Spring 2013 (1:00-3:00pm, Friday, March 15) Instructor: Prof Tejada Problem #1 (20 points): Problem #2 (20 points): Problem #3 (20 points): Problem #4 (20 points): Problem #5 (20 points): Total (100 points): (This exam is closed book, closed notes, closed everything. No cheat sheet allowed. No calculators, cell phones, or any electronic gadgets. Will adhere to Basic Rules on the Reviews lecture slides. To be eligible for regrades, you must write your entire exam in ink. ) 1

2 Problem 1. (20 points) Short Answer Questions a) (4 points) What is a reference variable and how do you declare it? Why use a reference variable instead of a pointer? 1pt : It is an alias for another variable. 1pt: int &x; 2pts: As a reference parameter because it has simpler syntax, and when you do not want to change the address stored in the pointer. b) (4 points) What is an array? What is a class? What is the main difference between an array and a class? When would you use a class instead of an array? 1pt: collection of elements of the same type and meaning 1pt: collection of both data members and methods 1pt: In classes members can have different data types and have different meanings 1pt: when you want to represent a real world object, with different types & meanings c) (4 points) Why do computer scientists know binary? Why hex? 1pt: The computer memory is transistors that store high or low voltage 0 represents low voltage, 1 is high voltage 1pt: computer memory is a collection of binary strings 1pt: Hex can be use to represent long binary strings 1pt: commonly used to represent memory address d) (4 points) Why use pointers? 1pt: Share access to one copy of data 1pt: efficiency in time and memory for pass by reference 1pt: dynamic data structures 1pt: precise control of allocation/deallocation e) (4 points) Why would you want to dynamically allocate memory? Where in memory is memory dynamically allocated from? 1pt: efficiency in memory management 1pt: allocate data structure of specific size at run time 1pt: the allocated memory can persist after the function executes 1pt: the heap 2

27 27 p q b) (4 points What is the output of the following C++ code?

3 Problem 2. What does this code do? (20 points) a) (4 points) What is the output of the following C++ code? int x = 35; int y = 46; int *p = &x; int *q = &y; *p = 97; p = q; *p = 27; cout<<x<<" "<<y<<endl; cout<<*p<<" "<<*q<<endl; x 35 p x 97 y 46 q y p q b) (4 points What is the output of the following C++ code? int num; int *listptr; int *temp; listptr = new int[5]; num = 8; temp = listptr; for (int j = 0; j < 5; j++) *listptr = num; num = num + 2; listptr++; for (int k = 0; k < 5; k++) cout << temp[k] << " "; j num prints out:

4 c) (12 points) What is the output of the following program? #include <iostream> using namespace std; void find(int a, int &b, int *c) int temp; *c = a + b; temp = a; a = b; b = 2 * temp; int main() int one, two, three; int *ptr; one = 5; two = 10; three = 15; ptr = &one; find(one, two, &three); cout << one << ", " << two << ", " << three << endl; One 5 Two 10 Three 15 A 10 b c Temp find(two, one, &three); cout << one << ", " << two << ", " << three << endl; One 20 Two 10 Three 15 A 5 b c Temp

5 find(three, two, &one); cout << one << ", " << two << ", " << three << endl; One 25 Two 30 Three 15 A 15 b c Temp find(two, three, ptr); cout << one << ", " << two << ", " << three << endl; One 45 Two 30 Three 60 A 30 b c Temp return 0; Problem 3. Debugging (20 points) (a) The program below only increments the first element of the array data. void increment(int *x) (*x)++; int main() int data[10] = 9,8,7,6,5,4,3,2,1,0; int *ptr; ptr=data; for (int i=0; i<10; i++) increment(ptr); ptr++; cout << data[i] << endl; return 0; (10 points) Insert one line of code into the main function so that the increment function can increment each element in array data. 5

6 (b) How would you change this code to swap the values of x and y? void swapit(int x, int y) int temp; temp = x; x = y; y = temp; int main() int x=5,y=7; swapit(x,y); cout << "x=" << x << " y="; cout << y << endl; (5 points) Using reference parameters: void swapit(int &x, int &y) (5 points) Using pointers: void swapit(int *x, int *y) int temp; 1pt: temp = *x; 2pt:*x = *y; 1pt:*y = temp; int main() int x=5,y=7; swapit(&x,&y); cout << "x=" << x << " y="; cout << y << endl; 6

7 Problem 4. (20 points) Pointers & Dynamic Memory Allocation Given the struct studenttype definition: struct studenttype string name; double gpa; int sid; char grade; ; a)(10 points) Write a function named calculateavg that will calculate the average gpa for all students enrolled in a course. The input parameters are a pointer to a dynamically allocated array of studenttype and the number of students enrolled in the class. The function should deallocate the array after the average is computed. Use this function header: double calculateavg(studenttype *course, int size) double sum = 0; for (int i=0; i<size; i++) sum+= course[i].gpa; delete [] course; return sum/size; b)(10 points) Write a function to dynamically create an array of students and return a pointer to the array. The function should ask the user for input on the number of students to create the array and ask the user to input the name, gpa, sid, grade for each student object in the array. Assume each student in the array is of type studenttype given above. studenttype *enrollstudents() int size = 0; cout << Enter size: << endl; cin >> size; studenttype *CScourse = new studenttype[size]; for (int i=0; i<size; i++) cout << Enter name: ; cin >> CScourse[i].name; cout << Enter gpa: ; cin >> CScourse[i].gpa; cout << Enter sid: ; cin >> CScourse[i].sID; cout << Enter grade: ; cin >> CScourse[i].grade; return CScourse; 7

8 Problem 5. struct & Classes & (20 points) Given the following class and struct definitions: //struct Pixel holds the red, green, and blue values for //one pixel for an image matrix. As unsigned char //variables, R, G, B have 8 bits of memory. struct Pixel unsigned char R; //Red value unsigned char G; //Green value unsigned char B; //Blue value ; //class Picture creates, manipulates, and maintains a image //matrix of pixels class Picture ; public: Picture(); //Constructor Picture(int wid, int ht); //constructs matrix of Pixel ~Picture(); //Destructor void show();//prints out a matrix of Pixels // returns RGB value of a pixel in the matrix at (y,x) int getpixelcolor(int x, int y); //sets the RGB values of pixel in the matrix at (y,x) //R,G,B as integers take input in decimal void setpixelcolor(int x, int y, int R, int G, int B); int getheight(); //returns height of image int getwidth(); //returns width of image private: Pixel **image_data; // 2d matrix of pixels int width; //width of image matrix int height; //height of image matrix 8

9 a) (10 points) What will this code printout: const int HEIGHT = 10; const int WIDTH = 10; Picture pic1(width,height); for (int i=0; i<width; i++) pic1.setpixelcolor(i,0,0,0,0); for (int i=0; i<width; i++) pic1.setpixelcolor(i,height-1,0,0,0); for (int j=0; j<height; j++) pic1.setpixelcolor(0,j,0,0,0); for (int j=0; j<height; j++) pic1.setpixelcolor(width-1,j,0,0,0); pic1.show(); Fill in the matrix below to show what the statement pic1.show()will print out for each pixel of the picture. For R=0x0, G=0x0, B=0x0 the pixel color is black. HEIGHT WIDTH x y 9

10 b) (10 points) Write a function that takes a pointer to a picture object as an input parameter, as well as the width and height. The function then changes the pixel color of picture object for the pixels shown below in the case of width = 10 and height = 10. The function should draw a red X on the picture with the first diagonal starting at 0,0 and with the second diagonal starting at 0, width- 1. The red pixel color is R=0xFF, G=0x9, B=0x0. Note: this function should work for all values of width and height. WIDTH x HEIGHT y void cross(picture *pic, int width, int height) if (width >0) && (height >0) //first diagonal for (int i=0; i<width; i++) if (i < height) pic->setpixelcolor(i,i,255,9,0); //second diagonal for (int i=width-1; i>=0; i--) if ((width-1-i) < height) pic->setpixelcolor(i,width-1-i,255,9,0); 10

Problem 1. Multiple Choice (choose only one answer)

Problem 1. Multiple Choice (choose only one answer) Practice problems for the Final (Tuesday, May 14 4:30-6:30pm MHP 101). The Final Exam will cover all course material. You will be expected to know the material from the assigned readings in the book, the