Midterm Exam 1 Solutions C Programming Dr. Beeson, Spring 2009

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1 Midterm Exam 1 Solutions C Programming Dr. Beeson, Spring 2009 March 10, 2009 Instructions: Please write your answers on the printed exam. Do not turn in any extra pages. No interactive electronic devices of any kind are allowed during the exam (no computer, no calculator). You can use your music player (if nobody else can hear it) if you put it on shuffle and don t punch any of its buttons during the exam. The exam is open notes, open book you can use any printed materials that you brought with you. Scoring: Five points per problem, total What is the ASCII code of upper-case A? 65 What is the ASCII code of the space character? Which of the following are legal ASCII codes? All those between 0 and 127 inclusive; thus (a) through (f). (a) 0 (b) 1 (c) 31 (d) 63 (e) 64 (f) 127 (g) 128 (h) 255 (i) What will be printed by the following code? { int i; for(i=0;i<5;i++) printf("%c", a +i); Answer: abcde 4. How many bytes are required to store the string "politics as usual"? One more than the number of characters visible. There are 17 characters visible (including the two spaces) so the answer is 18. 1

2 5. If you have to compute with integers that will go up to about a hundred million, what data type should you use? Answer: (a) int 6. If you have to compute with integers that will go up to about a hundred billion, what data type should you use? Answer: (c) long long. On most machines int and long go up to only about 2 billion. 7. Exhibit the pattern of 32 bits that is used to store the integer -1. Answer: Give a single printf command that will cause the following to be printed on TWO lines, with each line left-justified on the screen (without making any assumptions about what other printing commands might have just been executed). Number of giraffes: Number of elephants: Answer: printf("\n%s\n%s","number of giraffes:","number of elephants:"); 9. Suppose that price is an array of n doubles giving the price of silver for the years Exhibit two lines of code that will print a nice two-column table of these prices, with the years in the left-hand column and the prices in the right-hand column. (Do not worry about making a title, just print the data.) The first line should start with for and the second line with printf. Answer: for(i=0;i<n;i++) { printf("\n%d %10.2lf", i, prices[i]); 10. What will be printed by the following program? void f(int x) { x = x+1; { int x = 5; f(x); printf("\%d",x); Answer: 5 will be printed. One doesn t even have to read to definition of f to answer this question, one only has to read main to see that f cannot affect the value of x. 2

3 11. What will be printed by the following program? void f(int *x) { *x = *x+1; { int x = 5; f(&x); printf("\%d",x); Answer: 6 will be printed. Since the address of x is passed, the execution of f(&x) does affect the value of x. 12. Declare x to be an array of 1000 integers. int x[1000]; 13. Which of the following declarations would you use if you planned to read a string from the keyboard and put it in x? (a) char *x; (b) char x[128]; (c) char *x[80]; Answer: (b) 14. How many bytes will be allocated for an array of 100 longs? Answer: 400, assuming longs are 4 bytes each 15. What will be printed by the following code? { char x[80] = "You know the answer?" *(x+1) = a + 5; *(x+2) = x[15]; x[4] = 0; printf("\%s",x); Answer: Yfs. I had intended it to be Yes, but apparently, I can t count properly. 16. Suppose x is an array of integers, and we have just executed this code: for(i=0;i<10;i++) x[i] = i+1; Suppose that x[0] is stored at address What is the value of each of the following expressions? (a) x 4530 (b) &x[0] 4530 (c) *x 1 (d) x[1] 2 (e) &x[1] 4534; four bytes beyond x 3

4 (f) x ; this is the same as &x[2] (g) *(x+2) 3; the given expression simplifies to x[2]. (h) *(&x[2] +1) 4; the given expression simplifies to x[3]. 17. In the following code, identify the (a) local variables: sum, i,z,i (b) global variables: username (c) formal parameters: x, n (d) actual parameters: z, 10 Please write your answers above, not on the code below. { char *username = "Jack the Ripper"; double average( double *x, int n) { double sum=0.0; int i; for(i=0;i<n;i++) sum = sum + x[i]; return sum/n; { double z[10]; int i; for(i=0;i<10;i++) z[i] = i; printf("\%d",average(z,10)); 18. What function from the standard C library is this? int mysteryfunction(char *x) { char *marker; int count = 0; for(marker = x; *marker; ++marker) ++ count; return count; Answer: this is strlen. 19. Is the following code for strcpy correct? If not, correct it. void strcpy( char *destination, char *source) { char *marker, *t; for(marker = source, t = destination; *marker; marker++, t++) *t = *marker; Answer: This code fails to put a null terminator at the end of the copied string. To fix that problem add one more line of code at the end: *t = 0;, or equivalently, *t = \0 ; 4

5 20. If you use a computer program to solve the equation x = cos x, representing numbers as doubles, which of the following would be the answer you could expect to get? (a) (b) (c) (d) Answer: (c), since doubles have about 15 decimal digits of precision. 5