EE 312 Fall 2017 Midterm 1 October 12, 2017

Transcription

1 EE 312 Fall 2017 Midterm 1 October 12, 2017 Name: EID: Recitation time: Recitation TA (circle one): Colin Huy Give clear, legible answers. If you give more than one answer, we will randomly choose one to grade, so clearly mark out any answer you do not want us to grade. Write all code in C. The proctors will not answer questions about the course material or about the content of the exam. If you think a question is ambiguous or has an error, state your assumptions and answer based on those assumptions. For the questions on this test, you do not have to handle the possibility that the functions malloc and calloc might return NULL. Put away all electronics and earbuds. You are not allowed to use a calculator. You should only have out pencils. Silence your cellphone and put it away. Scratch paper is attached. Place your final answers on the test, not on scratch paper. Your answer must be legible to receive credit. When asked for Big-O, your answer must be the most restrictive correct Big-O function. For example, the function T(N) = 5N + 8 should be marked O(N), not O(N 2 ), even though it is correct under the formal definition of Big-O to say it s O(N 2 ). You should answer O(N) for this function, because that is the most restrictive correct answer. When you complete the test, show the proctor your UTID, give them the test and all the scratch paper, used or not, and leave the room quietly. GOOD LUCK Question Maximum Points Points Lost 1 (a-g, 2 pts ea) 14 2 (b and f: 6 pts ea, other parts, 4 pts ea) Total 100

2 1. Expression Values. In the space provided, write the value of each C expression. Assume the following declarations: char *s = SeriousCybernetics ; int A[2][3] = {4, 5, 6, 1, 2; char *t = Hello World ; char *v = Cyber ; int L[] = {3, 5, 2, 10; a) (char)(*v + 2) b) *(v+2) c) t[l[3] L[2]] d) L[(int)(s[1] t[10])] e) 105%20/2*4 f) s[strlen(s) 2] g) A[0][2]

3 2. Code Evaluation and Completion. Assume all necessary #includes are provided. If the code contains a syntax or compiler error, answer syntax error. If code results in an infinite loop, answer infinite loop. a) What is the output? char *s1 = gymnastics ; char arr[] = huffington ; for(int i = 0; i < 3; i++) { for(int j = i; j < 4+i; j++) { if(arr[j] < s1[j]) arr[j] = s1[j+1]; printf( %s, arr); b) What is the output? struct node { int key; struct node *next; ; typedef struct node *link; int main() { link x, y, t; x = malloc(sizeof(struct node)); y = malloc(sizeof(struct node)); xànext = y; xàkey = 1; yànext = x; yàkey = 1; for(t = x; tàkey < 25; t = tànext) { tàkey = xàkey + y à key; printf( %d\n, tàkey); c) What is the output? void func(int d[], int N) { d[0] += N; d[n-2] *= d[2]; int main() { int h[] = {3, 1, 5; func(h, 3); printf( %d\t%d\t%d, h[0], h[1], h[2]);

4 d) Fill in the blanks below so that the program prints the average length of the command line arguments (i.e., the arguments on the command line when the program is executed.) int main(int argc, char *argv[]) { Blank 1: int sum = 0; for(int i = 0; Blank 1 ; i++) { Blank 2: sum += Blank 2 ; Blank 3: printf( %le, (double) sum / Blank 3 ); e) Complete the code below so that scanf() is used to read as much as the string entered by the user as possible without causing a buffer overflow. The string that is read and stored in str should be nullterminated. char str[15]; printf( Please enter a string: ); Fill in the blank here: scanf( ); f) Assume function prototypes are provided in the file as needed. What is the output? int main() { Output in rectangle below: ghost(5); void ghost(int x) { int y = 0; for(int i = 1; i < x; i+= 2) { y = witch(y, skeleton(x, i)); printf( ghost: x = %d, y = %d\n, x, y); int witch(int x, int y) { x = 10 * x + y; printf( witch: x = %d, y = %d\n, x, y); return x; int skeleton(int x, int y) { return x / y % 2;

5 Programming. Assume all necessary #includes are provided in the file. 3. Write a function samerow() that takes a 2D array arr of ints, the number of rows and columns in arr, and two ints m and n. The function returns true if at least one row in arr contains both m and n, and false otherwise. If m and n are the same, return true if value m occurs at least once in some row, and false otherwise. For example, assume h is declared like this: int h[][3] = {{1, 2, 3, {2, 5, {8; Then samerow(3, 3, h, 1, 3) returns true, since 1 and 3 both occur in the 1 st row. And samerow(3, 3, h, 8, 8) returns true, since 8 occurs in the last row. bool samerow(int numrows,int numcols,int arr[numrows][numcols], int m, int n) { // add your code below

6 4. Write an improved version of strcat that takes two strings and returns a new string that contains the null-terminated concatenation of the two strings. Strings that are passed to your function should not be modified. You may not use any string.h functions unless you implement them yourself. For example: char *s1 = hello ; char *s2 = world ; char *ans = mystrcat(s1, s2); printf( %s\t%s\t%s, ans, s1, s2); The output will be: helloworld hello world char *mystrcat(char *first, char *sec) { // Put your code below

7 5. Write a function that takes a list pointer (i.e., the pointer NULL if the list is empty, and otherwise points to the first node in the list), an integer n to add to the list, and an integer pos indicating the position at which to add a new node containing n. Your function will return a pointer to the list. You do not need to handle the possibility that malloc will return NULL. So if pos is 1, add the new node at the beginning of the list, if pos is 2, add it so that it becomes the second node in the list, etc. If pos < 1, add n to the beginning of the list, and if pos is greater than the length of the list, add n to the end of the list. For example, if listptr points to the first node in this list (here each node is represented by the value of the num field in the node): 10 à 19 à 100 à 2 à NULL The call listptr = addatpos(listptr, 85, 2); will result in listptr pointing to: 10 à 85 à 19 à 100 à 2 à NULL This defines the type of the list nodes: struct node { int num; struct node *next; ; struct node *addatpos(struct node *list, int n, int pos) { // put your code below

8 Additional space for #5:

9 Big-O. 6. Consider the following function. The int N is the length of the array data. double function6(int data[], int N) { int r = 0; int limit = N/2; for(int i = 0; i < N; i++) { int s = data[i]; for(int j = 0; j < N; j++) { int t = data[j]; for(int k = limit - 2; k < limit; k++) { r += s * t * data[k]; return 1.0 * r / N; a) What is the function T(N) for function6? Recall that T(N) is a function that represents the actual number of executable statements for a function. N is the length of the data array. T(N) = b) What is the Big-O of function6? c) Assume that some function f is O(N 2 ). It takes 2 seconds for the function to run when N=2,000. What is the expected time in seconds for the function to run when N = 8,000?

10 Scratch Paper

11 Scratch Paper