Sample Midterm #2

  1. Parenthesize each of the following expressions fully, to show how they are evaluated in C. Hint: You do not need to know what the operators do to answer this problem.
    a  =  b  *  c  ==  2  
    a  =  b  &&  a  >  z  ?  x  =  y  :  z 
    a  =  s  .  f  +  x  .  y 
    a  =  b  >>  2  +  4
    c  =  getchar()  ==  EOF
  2. The following fragment of code will produce a segmentation fault since it tries to access memory using a NULL pointer:
    int *p;
    p = NULL;
    if (*p == 13)
    	printf(" got it!\n");
    Will the following fragment of code also produce a segmentation fault? Why or why not?
    int *p;
    p = NULL;
    if (p != NULL && *p == 13)
    	printf("got it!\n");
  3. Use the following code fragment to answer the questions below:
    i = 2;
    case 1:	printf("moo\n");
    case 2:	printf("baa\n");
    case 3:	printf("meep\n");
    case 4:	printf("sproing\n");
    1. What is the output of the above switch statement?
    2. What is the output if i were set to 3 rather than 2 in the first statement?
    3. What is the output if i were set to 0 rather than 2 in the first statement?

  4. Rewrite the following program without using break, continue, or goto.
    /* Count the number of a's  */
    /* in a line given as input */
    #include <stdio.h>
    #include <ctype.h>
    void main(void)
    	int num_a = 0;
    	int c;
    	c = getchar();
    	while(1) {
    		if (c == '\n')
    		if (isdigit(c))
    		if (c == 'a')
    			goto add_num_a;
    		c = getchar();
    		goto end_loop;
    		goto get_next_char;
    	printf("%d\n", num_a);
  5. What does the following segment of code print?
    char *c[] = {
    char **cp[] = {  c+3, c+2, c+1, c };
    char ***cpp = cp;
    	printf("%s", **++cpp );
    	printf("%s ", *--*++cpp+3 );
    	printf("%s", *cpp[-2]+3 );
    	printf("%s\n", cpp[-1][-1]+1 );
    Hint: Draw a picture of the arrays and the pointers.

  6. Here is a macro for computing the minimum of two numbers:
    #define	min(a, b)	((a) > (b) ? (b) : (a))
    and here is a function:
    int min(int a, int b)
    	return(a > b ? b : a);
    In the following code fragment, give the values of a, b, c, d, and e at the end if min is the above macro, and then if min is a function call:
    a = 2;
    b = 3;
    c = 4;
    d = min(++a, b);
    e = min(c++, b);
  • Here are three functions:
    int testandinc(int x)
    int p1testandinc(int *x)
    int p2testandinc(int *x)
    Give the values of a, b, c, d, e, f, and the elements of the array at the end of this code fragment. (Remember that b and c are pointers, so express their values by using the variables they point to; for example, if b poointed to a, then write b's value as &a.)
    int a = 2;
    int arr[3] = { 3, 4, 5 };
    int *b = arr;
    int *c = &arr[1];
    d = testandinc(a);
    e = p1testandinc(b);
    f = p2testandinc(c);
  • Some UNIX questions.
    1. Rewrite the following so that it uses no intermediate files:
      sed 's/:.*//' /etc/passwd > /tmp/X1
      sort < /tmp/X1 > /tmp/X2
      uniq -u < /tmp/X2 > usernames
    2. Heidi is in her home directory, /usr/heidi. How would she create a subdirectory called heidi-hw1?
    3. How would she copy the files control.c and select_from_menu.c from her home directory to that subdirectory?
    4. How would she create a tar archive, in her home directory, of that directory and its contents?
    5. How would she encode that archive into a printable representation suitable for mailing to her friendly grader?
    6. David wants to list all the files in his home directory that have names ending in rc. He types the command
      ls *rc
      and gets the following output:
      He knows that he has two other files with names that end in rc, namely .cshrc and .exrc. He wonders why the command did not print them. Explain why. What command should he have given to list all files ending in rc, even those which begin with a "."?