Question 1 (4 points)
A C program foo is invoked by the command line: foo Go 2008 Wisconsin Badgers
What is the value of argc? What is the type of argv[2]?

argc is 5.
The type of argv[2] is the type of *char.

Question 2 (4 points)
What is the purpose of the program counter? How does an instruction like sub d, e, f change value of the program counter?


The PC gives the address in memory of the next instruction to be executed.
This instruction will increment the PC by its length (e.g., 4 bytes).

Question 3 (8 points)
This question is about logical operations, but it is presented in C to be unambiguous.

#include <stdio.h>
#include <stdlib.h>
int main()
{
 unsigned int x = 0xddccbbaa, y = 0x000000ff;
 unsigned int r, s, t, u, v;
 r = x & y;             /* bitwise and */
 s = x | y;             /* bitwise or */
 t = x >> 8;            /* shift right */
 u = ((x && y) == 0);   /* do you remember? */

 ...
}

What are the final values, in hexadecimal, of r, s, t, and u?

 r = 0x000000aa

 s = 0xddccbbff

 t = 0x00ddccbb

 u = 0x0

Question 4 (9 points)
What will this program print? Partial credit will be given only if you draw the six memory locations and get close to the right answer.

#include <stdio.h>
#include <stdlib.h>
int main()
{
 int i, j, k;
 int *p, *q, *r;
 /* initialize */
 i = 4; j = 6; k = 8;
 p = &i; q = &j; r = &k;

 p = q;
 *p  += 2;
 if (*p==*r) *q = 0;

 printf("i=%d, j=%d, k=%d\n", i, j, k);
}

4 0 8

Question 5 (9 points)
Please complete the C code for the recursive function factorial with comments explaining why you do something.

/* F! = F*(F-1)! for F > 0     */
/* 0! = 1                      */
/* Example: 4! = 4*3*2*1 = 24  */

   int   factorial(  int   f)

{


if (  f==0      ) {
     return 1;

}

else {

     return (    f *    factorial(f-1)         );
 }
}

Question 6 (6 points)
Consider the following function that contains at least one error. Please explain the error(s).

/* The strcmp() function compares the two strings str1 and str2.                      */
/* It returns an integer less than, equal to, or greater than zero if str1 is found,  */
/*  respectively, to be less than, to match, or be greater than str2.                 */

int strcmp(char *str1, char *str2)
{
    int i;
    for (i = 0; str1[i] == str2[i]; i++){
        if (str1[i] == '\0')
            return 0;
    }
    return str2[i] - str1[i];
}

Less and greater than are reversed. The last line should be:
return str1[i] - str2[i];

Question 7 (10 points total) Consider 32-bit, two's complement integers A, B, Sum and Diff. Let sign(X) denote the most-significant (sign) bit of X. For example, if A=0x07ffffff then sign(A)==0. Recall that for two's complement integer ADDITION (Sum = A + B), OVERFLOW occurs when:

((sign(A)==0)&&(sign(B)==0)&&(sign(Sum)==1)) || ((sign(A)==1)&&(sign(B)==1)&&(sign(Sum)==0))

(a) (4 points) Assume that A=x7fffffff and B=0x00000001. Does Sum = A + B overflow? Does Diff = A - B overflow?

A = 2^31-1 (largest 32-bit two's complement integer)
B = +1
A + B = 2^31 = 0x80000000 ==> Overflow
A - B = 2^31 - 2 ==> No Overflow

(b) (6 points) If A and B can take any value, write an expression for OVERFLOW with two's complement SUBTRACTION (Diff = A - B):

((sign(A)==0)&&(sign(B)==1)&&(sign(Diff)==1)) || ((sign(A)==1)&&(sign(B)==0)&&(sign(Diff)==0))