CS计算机代考程序代写 Name: ID#: X.500:

Name: ID#: X.500:

CS 2021: Practice Exam 1
Fall 2021

University of Minnesota

Exam period: 20 minutes
Points available: 50

Problem 1 (15 pts): Nearby is a small C pro-
gram which makes use of arrays, pointers, and func-
tion calls. Fill in the tables associated with the ap-
proximate memory layout of the running program at
each position indicated. Assume the stack grows to
lower memory addresses and that the sizes of C
variable types correspond to common 64-bit systems.

1 #include
2 void flub(double *ap, double *bp){
3 int c = 7;
4 if(*ap < c){ 5 *ap = bp[1]; 6 } 7 // POSITION B 8 return; 9 } 10 int main(){ 11 double x = 4.5; 12 double arr[2] = {3.5, 5.5}; 13 double *ptr = arr+1; 14 // POSITION A 15 flub(&x, arr); 16 printf("%.1f\n",x); 17 for(int i=0; i<2; i++){ 18 printf("%.1f\n",arr[i]); 19 } 20 return 0; 21 } POSITION A |--------+--------+---------+-------| | Frame | Symbol | Address | Value | |--------+--------+---------+-------| | main() | x | #3064 | | | | arr[1] | #3056 | | | | arr[0] | | | | | ptr | | | | | i | | ? | |--------+--------+---------+-------| POSITION B |--------+--------+---------+-------| | Frame | Symbol | Address | Value | |--------+--------+---------+-------| | main() | x | #3064 | | | | arr[1] | #3056 | | | | arr[0] | | | | | ptr | | | | | i | | ? | |--------+--------+---------+-------| | flub() | | | | | | | | | | | | | 7 | |--------+--------+---------+-------| Problem 2 (10 pts): Fill in the following ta- ble of equivalent ways to write these 8 bit quan- tities. There are a to- tal of 9 blanks to fill in and the first column indi- cates which blanks occur in which lines. Assume two’s complement encod- ing for the signed decimal column. |----------+-----------+------+-------+----------+---------| | | | | | Unsigned | Signed | | Blank #s | Binary | Hex | Octal | Decimal | Decimal | |----------+-----------+------+-------+----------+---------| | | | | | | | | #1 #2 #3 | 0001 1011 | | 0033 | | | | | | | | | | | #4 #5 #6 | | 0xA5 | 0245 | | | | | | | | | | | #7 #8 #9 | | 0xC7 | | | -57 | |----------+-----------+------+-------+----------+---------| 1/ 2 WRITE ON EVERY PAGE – Name: Backgound: Write a short C code fragment (1-5 lines) using a C I/O function call to accomplish the stated task. Assume in each case there is a variable FILE *fh which has been opened appropriately for the I/O operation. Also assume that any variables mentioned have already been declared. Problem 3 (5 pts): Read three text floating point values from fh formatted as standard decimal point values into double variables r,u,t. Check if the read fails due to reaching the end of file; if so print the message None left. Problem 4 (5 pts): Write 8 characters from the beginning of array str to fh in binary format. #include
#include

// Struct to count positive/negative
// numbers in arrays.
typedef struct {

int poss, negs;
} pn_t;

pn_t *get_pn(int *arr, int len);
// Allocates a pn_t and initializes
// its field to zero. Then scans array
// arr increment poss for every 0 or
// positive value and negs for every
// negative value. Returns the pn_t
// with poss/negs fields set. If arr
// is NULL or len is less than 0,
// returns NULL.

int main(){
int arr1[5] = {3, 0, -1, 7, -4};
pn_t *pn1 = get_pn(arr1, 5);
// pn1: {.poss=3, .negs=2}
free(pn1);

int arr2[3] = {-1, -2, -4};
pn_t *pn2 = get_pn(arr2, 3);
// pn2: {.poss=0, .negs=3}
free(pn2);

int *arr3 = NULL;
pn_t *pn3 = get_pn(arr3, -1);
// pn3: NULL

return 0;
}

Problem 5 (15 pts): Nearby is a main() function demon-
strating the use of the function get pn(). Implement this func-
tion according to the documentation given. My solution is about
12 lines plus some closing curly braces.

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