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;
   switch(i){
   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')
   			break;
   		if (isdigit(c))
   			continue;
   		if (c == 'a')
   			goto add_num_a;
   get_next_char:
   		c = getchar();
   		goto end_loop;
   add_num_a:
   		num_a++;
   		goto get_next_char;
   end_loop:
   		;
   	}
   	printf("%d\n", num_a);
   	exit(0);
   }
   

5. What does the following segment of code print?

   char *c[] = {
   	"ENTER",
   	"NEW",
   	"POINT",
   	"FIRST"
   };
   
   char **cp[] = {  c+3, c+2, c+1, c };
   char ***cpp = cp;
   main()
   {
   	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);
   
   

int testandinc(int x)
{
	return(x++);
}
int p1testandinc(int *x)
{
	return(*x++);
}
int p2testandinc(int *x)
{
	return((*x)++);
}

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);