COS 126 MIDTERM 1, FALL

Transcription

1 COS 126 MIDTERM 1, FALL This test has 12 questions worth a total of 50 points. You have 120 minutes. The exam is closed book, except that you are allowed to use a one page cheatsheet. No calculators or other electronic devices are permitted. Give your answers and show your work in the space provided. Write out and sign the Honor Code pledge before turning in the test. I pledge my honor that I have not violated the Honor Code during this examination. Problem Score Problem Score Sub 1 Sub 2 Total Name: Login ID: Precept: 1 MF 10:00 Ben 2 MF 11:00 Kevin 3 MF 1:30 Lisa 4 MF 2:30 Kevin 5 M 7, F 2:30 Lisa 6 MF 10:00 Scott

2 2 PRINCETON UNIVERSITY 1. C basics. (5 points) What value gets printed by the following code fragment? Circle the correct answer. xx int cnt = 0; for (i = 0; i < 10; i++) for (j = 0; j < 10; j++) for (k = 0; k < 10; k++) if (2*i + j >= 3*k) cnt++; printf("%d\n", cnt); (a) 0 (b) 100 (c) 101 (d) 517 (e) C basics. (6 points) Complete the C program (in the space provided below) so that it prints out the following table. Do not define any other variables. xx 10,45 20,45 30,45 40,45 50,45 60,45 70,45 80,45 90,45 10,40 20,40 30,40 40,40 50,40 60,40 70,40 80,40 90,40 10,35 20,35 30,35 40,35 50,35 60,35 70,35 80,35 90,35 10,30 20,30 30,30 40,30 50,30 60,30 70,30 80,30 90,30 10,25 20,25 30,25 40,25 50,25 60,25 70,25 80,25 90,25 #include <stdio.h> int main(void) { int x, y; return 0;

3 COS 126 MIDTERM 1, FALL Unix. (5 points) xx #include <stdio.h> int main(void) { int x, y; scanf("%d", &x); while(scanf("%d", &y)!= EOF) { if (x < y) { printf("%d ", x); x = y; else printf("%d ", y); printf("%d\n", x); return 0; Suppose we compile the above program, and that the file input.txt contains: and that the following Unix commands are executed. % a.out < input.txt % a.out < input.txt a.out % a.out < input.txt a.out a.out % a.out < input.txt a.out a.out a.out % a.out < input.txt a.out a.out a.out a.out % a.out < input.txt a.out a.out a.out a.out a.out Which of the following is not printed as the output to one of the above commands. (a) (b) (c) (d) (e) (f)

4 4 PRINCETON UNIVERSITY 4. Arrays. (5 points) Suppose that b[] is an array of 100 elements, with all entries initialized to 0, and a[] is an array of N elements, each of which is an integer between 0 and 99. What is the effect of the following loop? for (j = 0; j < N; j++) b[a[j]]++; (a) Sets b[0] to 0, b[1] to 1, b[2] to 2, etc. (b) Sets b[0] to the number of 0 s in a[], b[1] to the number of 1 s in a[], etc. (c) Sets b[0] to a[0], b[1] to a[0] + a[1], b[2] to a[0] + a[1] + a[2], etc. (d) Sets all entries of b[] to 1. (e) Out-of-bounds array access. (f) None of the above. 5. Modular programming. (3 points) Which of the following best describes the file stdio.h? (a) client (b) function (c) implementation (d) interface (e) program 6. Programming abstractions. (3 points) Match each of the following terms with a phrase that describes it by putting the letter associated with the phrase to the left of the term. array data type function program struct (a) heterogeneous collection of values (b) homogeneous collection of values (c) sequence of statements (d) set of functions (e) set of values and collection of operations on those values

5 COS 126 MIDTERM 1, FALL Queues and ADT s. (4 points) Consider the following program that uses a FIFO queue. What does it print out? Recall QUEUEput() inserts an item onto the queue, and QUEUEget() deletes and returns an item. xx #include <stdio.h> #include "QUEUE.h" int main(void) { int i; QUEUEinit(); for (i = 0; i < 10; i++) QUEUEput(i); while (!QUEUEisempty()) { for (i = 0; i < 3; i++) QUEUEput(QUEUEget()); printf("%d ", QUEUEget()); printf("\n"); return 0; (a) (b) (c) (d) (e) (f) (g) (h) The program crashes due to an array out-of-bounds error. (i) The program crashes due to a queue underflow error. (j) None of the above.

6 6 PRINCETON UNIVERSITY 8. Recursion. (4 points) Consider the following Fibonacci function that was run in lecture. Suppose it takes 1 second to compute F(30). Approximately how long does it take to compute F(240), including time to print to the screen and ignoring any overflow. xx int F(int n) { if (n ==0 n == 1) return n; else return F(n-1) + F(n-2); (a) less than 210 nanoseconds (b) 1 second (c) 7 seconds (d) 8 seconds (e) 9 seconds (f) 210 seconds (g) 8 hours (h) 210 days (i) more than 8 millennia 9. Quicksort. (5 points) Suppose that the standard (in-place) recursive quicksort is used to sort an array containing the following keys: E A S Y Q U E S T I O N Which of the following does not represent the contents of the array at some point during the sort? (a) A E E I N O Q S S T U Y (b) A E E I N U Y S T S O Q (c) E A I E N O Q S S T U Y (d) E A I E N U Y S T S O Q (e) E A I Y Q U E S T S O N (f) E A S Y Q U E S T I O N

7 COS 126 MIDTERM 1, FALL Recursion. (4 point) Consider the following recursive function. What is f(0)? Write and circle your answer. Warning: high degree of difficulty. xx int f(int x) { if (x > 1000) return x - 4; else return f(f(x+5));

8 8 PRINCETON UNIVERSITY 11. TOY. (5 points) Consider the following TOY program. 10:B006 11:B101 12: : :0000 Suppose the above program is loaded, the program counter is set to 10, and the machine is started. What are the 16 bits stored in register R1 upon termination of the above program? (a) (b) (c) (d) (e) (f) (g) (h) (i) program does not terminate (j) none of the above 12. All done. (1 point) T T F F On the front of the exam, I have written my name and arizona login, circled my precept number, and written and signed the honor code.

9 COS 126 MIDTERM 1, FALL TOY Instructions INSTRUCTION FORMATS Format 1: opcode, r0, r1, and r2 (0, 1, 2, 3, 4, C, D) Format 2: opcode, r0, and 8-bit addr (5, 6, 7, 8, 9, A, B, E, F) Indexed addressing (for Format 2): if leading bit of r0 digit is 1, then addr = r1 + r2 TRANSFER between registers and memory 9: load r0 <- mem[addr] A: store mem[addr] <- r0 B: load constant r0 <- addr ARITHMETIC operations 1: add r0 <- r1 + r2 2: subtract r0 <- r1 - r2 3: multiply r0 <- r1 * r2 LOGICAL operations C: xor r0 <- r1 ^ r2 D: and r0 <- r1 & r2 E: shift right r0 <- r0 >> addr F: shift left r0 <- r0 << addr CONTROL 0: halt halt 4: system call print r0 on tty 5: jump pc <- addr 6: jump if positive if (r0 > 0) pc <- addr 7: jump and count r0-- if (r0!= 0) pc <- addr 8: jump and link r0 <- pc pc <- addr

10 10 PRINCETON UNIVERSITY This page is for scratchwork.

11 COS 126 MIDTERM 1, FALL This page is for scratchwork.

12 12 PRINCETON UNIVERSITY This page is for scratchwork.