GATE CS 2018

Consider the following C program:

#include <stdio.h>
void fun1(char *s1, char *s2) {
  char *temp;
  temp = s1;
  s1 = s2;
  s2 = temp;
}
void fun2(char **s1, char **s2) {
  char *temp;
  temp = *s1;
  *s1 = *s2;
  *s2 = temp;
}
int main() {
  char *str1 = "Hi", *str2 = "Bye";
  fun1(str1, str2);
  printf("%s %s", str1, str2);
  fun2(&str1, &str2);
  printf("%s %s", str1, str2);
  return 0;
}

The output of the program above is

Consider the following C program.

#include <stdio.h>
struct Ournode {
  char x, y, z;
};

int main() {
  struct Ournode p = {'1', '0', 'a' + 2};
  struct Ournode *q = &p;
  printf("%c, %c", *((char *)q + 1), *((char *)q + 2));
  return 0;
}

The output of this program is:

Consider the following C code. Assume that

unsigned long int

type length is 64 bits.

unsigned long int fun(unsigned long int n) {
        unsigned long int i, j = 0, sum = 0;
        for( i = n; i > 1; i = i/2) j++;
        for( ; j > 1; j = j/2) sum++;
        return sum;
}

The value returned when we call

fun with the input 2⁴⁰ is

The following are some events that occur after a device controller issues an interrupt while process L is under execution. (P) The processor pushes the process status of L onto the control stack. (Q) The processor finishes the execution of the current instruction. (R) The processor executes the interrupt service routine. (S) The processor pops the process status of L from the control stack. (T) The processor loads the new PC value based on the interrupt. Which of the following is the correct order in the which the events above occur?

Consider a simple communication system where multiple nodes are connected by a shared broadcast medium (like Ethernet or wireless). The nodes in the system use the following carrier-sense the medium access protocol. A node that receives a packet to transmit will carrier-sense the medium for 5 units of time. If the node does not detect any other transmission in this duration, it starts transmitting its packet in the next time unit. If the node detects another transmission, it waits until this other transmission finishes, and then begins to carrier-sense for 5 time units again. Once they start to transmit, nodes do not perform any collision detection and continue transmission even if a collision occurs. All transmissions last for 20 units of time. Assume that the transmission signal travels at the speed of 10 meters per unit time in the medium.

Assume that the system has two nodes P and Q, located at a distance d meters from each other. P starts transmitting a packet at time t = 0 after successfully completing its carrier-sense phase. Node Q has a packet to transmit at time t = 0 and begins to carrier-sense the medium.

The maximum distance d (in meters, rounded to the closest integer) that allows Q to successfully avoid a collision between its proposed transmission and P’s on going transmission is _______ .

Note -This was Numerical Type question.

Consider the weights and values of items listed below. Note that there is only one unit of each item.

The task is to pick a subset of these items such that their total weight is no more than 11 Kgs and their total value is maximized. Moreover, no item may be split. The total value of items picked by an optimal algorithm is denoted by V_opt. A greedy algorithm sorts the items by their value-to-weight ratios in descending order and packs them greedily, starting from the first item in the ordered list. The total value of items picked by the greedy algorithm is denoted by V_greedy. The value of V_opt − V_greedy is ______ . 

Consider a process executing on an operating system that uses demand paging. The average time for a memory access in the system is M units if the corresponding memory page is available in memory, and D units if the memory access causes a page fault. It has been experimental measured that the average time taken for a memory access in the process is X units. Which one of the following is the correct expression for the page fault rate experienced by the process?

Consider the following program written in pseudo-code. Assume that x and y are integers.

Count (x, y) {
    if (y !=1 ) {
        if (x !=1) {
            print("*");
            Count (x/2, y);
        }
        else {
            y=y-1;
            Count (1024, y);
        }
    }
}

The number of times that the

print

statement is executed by the call

Count(1024, 1024)

is _______ .

Note -

This was Numerical Type question.

Consider a storage disk with 4 platters (numbered as 0, 1, 2 and 3), 200 cylinders (numbered as 0, 1, … , 199), and 256 sectors per track (numbered as 0, 1, … 255). The following 6 disk requests of the form [sector number, cylinder number, platter number] are received by the disk controller at the same time:

[120, 72, 2], [180, 134, 1], [60, 20, 0], [212, 86, 3], [56, 116, 2], [118, 16, 1]

Currently head is positioned at sector number 100 of cylinder 80, and is moving towards higher cylinder numbers. The average power dissipation in moving the head over 100 cylinders is 20 milliwatts and for reversing the direction of the head movement once is 15 milliwatts. Power dissipation associated with rotational latency and switching of head between different platters is negligible.

The total power consumption in milliwatts to satisfy all of the above disk requests using the Shortest Seek Time First disk scheduling algorithm is ______ .

Note -This was Numerical Type question.

Let G be a simple undirected graph. Let T_D be a depth first search tree of G. Let T_B be a breadth first search tree of G. Consider the following statements. (I) No edge of G is a cross edge with respect to T_D. (A cross edge in G is between two nodes neither of which is an ancestor of the other in T_D). (II) For every edge (u, v) of G, if u is at depth i and v is at depth j in T_B, then ∣i − j∣ = 1. Which of the statements above must necessarily be true?