DSSSB TGT / PGT · Topic-wise previous year questions
Computer Science Previous Year Questions (page 35)
2444 Computer Science questions asked in DSSSB TGT / PGT previous year papers, each with the correct answer and explanation. Read them free on UTpaper, or attempt the full papers as timed online tests.
In FCFS scheduling, the average waiting time is affected most by:
Aprocess priority
Bpreemption
Cthe arrival order of processes
DCPU clock speed
Show answerHide answer
Correct answer: (C) the arrival order of processes
Explanation
FCFS runs processes strictly in arrival order, so if a long process arrives first, every later process waits behind it (the convoy effect). The order of arrival therefore decides the average waiting time.
Which of the following SQL statements will retrieve the lowest value from a column named
'Price' in a table named 'Products'?
ASELECT MIN(Price) FROM Products;
BSELECT LOWEST(Price) FROM Products;
CSELECT TOP 1 Price FROM Products ORDER BY Price ASC;
DSELECT Price FROM Products WHERE Price = MIN(Price);
Show answerHide answer
Correct answer: (A) SELECT MIN(Price) FROM Products;
Explanation
The aggregate function MIN() returns the smallest value in a column. LOWEST() does not exist, and an aggregate cannot be used directly in a WHERE clause.
Which of the following scenarios indicates successful connection establishment in TCP?
AOnly the SYN is sent and received
BData packets are transmitted without SYN packets
CSYN, SYN-ACK and ACK packets are exchanged
DOnly the SYN-ACK is sent
Show answerHide answer
Correct answer: (C) SYN, SYN-ACK and ACK packets are exchanged
Explanation
TCP sets up a connection with a three-way handshake: the client sends SYN, the server replies SYN-ACK and the client answers ACK. Only after this exchange is the connection established.
Select the correct SQL query that returns all students whose results are greater than the
average result of their respective departments.
ASELECT stu_id
FROM student
WHERE result > (SELECT AVG(result) FROM student GROUP BY dept_id);
BSELECT stu_id
FROM student
WHERE result > AVG(result) GROUP BY dept_id;
CSELECT stu_id
FROM student s
WHERE result > (SELECT AVG(s.result) FROM student);
DSELECT stu_id
FROM student s
WHERE result > (SELECT AVG(result) FROM student WHERE dept_id = s.dept_id);
Show answerHide answer
Correct answer: (D) SELECT stu_id
FROM student s
WHERE result > (SELECT AVG(result) FROM student WHERE dept_id = s.dept_id);
Explanation
To compare each student with their own department's average, the subquery must be correlated: WHERE dept_id = s.dept_id links it to the outer row. Option A's subquery returns several averages, and B uses an aggregate in WHERE, which is not allowed.
Which of the following is true about the page table?
AThe page table contains the data of each process.
BThe page table maps virtual addresses to physical addresses.
CThe page table is used only in non-paging systems.
DThe page table stores the instructions for memory management.
Show answerHide answer
Correct answer: (B) The page table maps virtual addresses to physical addresses.
Explanation
A page table holds, for each page of a process, the frame number in physical memory, so it translates virtual (logical) addresses into physical addresses. It holds no process data or instructions.
Which firewall type acts as an intermediary for requests between a client and a server?
AProxy firewall
BStateful
CPacket-filtering
DCircuit-level gateway
Show answerHide answer
Correct answer: (A) Proxy firewall
Explanation
A proxy firewall (application-level gateway) sits between client and server: it receives the client's request and makes its own request to the server, so the two never connect directly.
What is the role of the 'resource-allocation graph' in deadlock avoidance?
AScheduling I/O operations
BDetecting existing deadlocks
CRepresenting the state of system resources and processes
DTracking CPU usage
Show answerHide answer
Correct answer: (C) Representing the state of system resources and processes
Explanation
A resource-allocation graph shows processes, resources, and request and assignment edges. Using it (with claim edges), the system can check whether granting a request could create a cycle, and so avoid deadlock.
Which of the following protocols supports multiplexing in transport layer?
AHTTP
BFTP
CUDP
DSMTP
Show answerHide answer
Correct answer: (C) UDP
Explanation
Transport-layer protocols such as UDP and TCP multiplex several application streams over one network connection using port numbers. HTTP, FTP and SMTP are application-layer protocols.
How does TCP ensure a clean termination of both sides during a normal connection release?
ABy resending SYN packets
BBy encrypting all termination packets
CBy entering the LISTEN state after termination
DBy sending FIN and ACK packets sequentially
Show answerHide answer
Correct answer: (D) By sending FIN and ACK packets sequentially
Explanation
In a normal TCP release, each side sends a FIN and the other side acknowledges it with an ACK (usually four segments). This closes both directions of the connection cleanly.
In order to grant a user named 'Deepak' the ability to read data from a table called
'Customers', which SQL statement should be used?
AGRANT SELECT ON Customers TO Deepak;
BGRANT READ ON Customers TO Deepak;
CGRANT ACCESS ON Customers TO Deepak;
DGIVE SELECT ON Customers TO Deepak;
Show answerHide answer
Correct answer: (A) GRANT SELECT ON Customers TO Deepak;
Explanation
SELECT is the privilege that allows reading rows from a table, so GRANT SELECT ON Customers TO Deepak; is correct. READ and ACCESS are not SQL privileges, and GIVE is not an SQL command.
int a = 4, b = 8, c = 6;
if (a > b) {
if (a > c) {
System.out.println("a is the largest");
} else if (b > c) {
System.out.println("b is the largest");
} else {
System.out.println("c is the largest");
}
} else {
if (b > c) {
System.out.println("b is the largest");
} else {
System.out.println("c is the largest");
}
}
What is the output of the above code snippet( Assume that it is written inside main() function
)?
Ac is the largest
Bb is the largest
Ca is the largest
DCompilation error
Show answerHide answer
Correct answer: (B) b is the largest
Explanation
a > b (4 > 8) is false, so the outer else block runs. There b > c (8 > 6) is true, so "b is the largest" is printed.
Which method binding is associated with method overriding in Java?
AStatic binding
BDynamic binding
CEarly binding
DCompile-time binding
Show answerHide answer
Correct answer: (B) Dynamic binding
Explanation
Method overriding is resolved at run time from the actual object type. This is dynamic (late) binding, the basis of runtime polymorphism. Static or early binding is used for overloading, private, static and final methods.
A 2D array B[4][5] is stored in row-major order. The base address of the array is 5000, and
each element occupies 2 bytes. What is the address of B[2][3]?
class Person {
private String name;
public Person(String name) {
this.name = name;
}
private void displayName() {
System.out.println("Name: " + name);
}
}
public class Test {
public static void main(String[] args) {
Person p = new Person("John");
p.displayName();
}
}
What will happen when the above code is compiled and executed?
ACompilation Error: The method displayName is not visible in Test.
BRuntime Error: The method displayName cannot be called.
CThe code will compile and display Name: John.
DCompilation Error: The field name is not visible in Test.
Show answerHide answer
Correct answer: (A) Compilation Error: The method displayName is not visible in Test.
Explanation
displayName() is private in Person, so it cannot be called from class Test. The compiler reports that displayName() has private access in Person.
What will be the output of the following code?
#include<stdio.h>
int main() {
int x=5,y;
y=x++ + ++x;
printf("%d",y);
return 0;
}
A11
Bcompile time error
C12
D10
Show answerHide answer
Correct answer: (C) 12
Explanation
x++ gives 5 (x becomes 6), then ++x makes x 7, so y = 5 + 7 = 12 on common compilers. Strictly, modifying x twice in one expression is undefined behaviour in C.
What will be the output of the following Java code? public class DoWhileExample {
public static void main(String[] args) {
int x = 10;
do {
System.out.println("x = " + x);
x++;
} while (x < 13);
}
}
Ax = 10
x = 11
x = 12
Bx = 10
Cx = 10
x = 11
DNo output
Show answerHide answer
Correct answer: (A) x = 10
x = 11
x = 12
Explanation
A do-while body runs before the test: it prints x = 10, 11 and 12, and stops when x becomes 13 because 13 < 13 is false.
What will be the output of the following code when the input is HelloWorld?
#include <stdio.h>
int main() {
char str[5]; // Buffer for input
int result = scanf("%4s", str);
if (result == 1) {
printf("Input: %s\n", str);
} else {
printf("Input error or no input.\n");
}
return 0;
}
AInput: Hell
BInput: Hello
CInput error or no input
DInput: HelloWorld
Show answerHide answer
Correct answer: (A) Input: Hell
Explanation
The width %4s makes scanf read at most 4 characters, so str gets "Hell" plus '\0' (fits in 5 bytes). scanf returns 1, so "Input: Hell" is printed.
If a, b are the inputs and y is the output of a two input AND logic gate, then which of the
following is the correct expression for the output of the AND logic gate?
Ay = a'.b'
By = a.b'
Cy = a'.b
Dy = a.b
Show answerHide answer
Correct answer: (D) y = a.b
Explanation
An AND gate gives 1 only when both inputs are 1, so y = a·b. The options with complemented inputs describe other functions.
Consider the below Code snippet:
class Calculator {
void calculate(int a, int b) {
class Multiply {
int product() {
return a * b;
}
}
Multiply multiply = new Multiply();
System.out.println("Product: " + multiply.product());
}
}
public class Main {
public static void main(String[] args) {
Calculator calculator = new Calculator();
calculator.calculate(5, 3);
}
}
What will be the output?
AProduct: 15
BProduct: 0
CRuntime Error.
DCompilation Error: Multiply cannot be defined inside calculate.
Show answerHide answer
Correct answer: (A) Product: 15
Explanation
Java allows a local class inside a method, and it can use the method's effectively final parameters a and b. product() returns 5 × 3 = 15, so "Product: 15" is printed.
What will be the output of the following code?
#include <stdio.h>
int main() {
if (5 > 10)
printf("5 is greater than 10");
else
printf("5 is not greater than 10");
return 0;
}
ANo output
BSyntax error
C5 is greater than 10
D5 is not greater than 10
Show answerHide answer
Correct answer: (D) 5 is not greater than 10
Explanation
5 > 10 is false, so the else branch runs and prints "5 is not greater than 10".
#include <stdio.h>
int main() {
FILE *file = fopen("input.txt", "r");
int value;
fscanf(file, "%d", &value);
fseek(file, 0, SEEK_SET);
fscanf(file, "%d", &value);
fclose(file);
printf("%d\n", value);
return 0;
}
What will be the output of the code if input.txt contains 42?
AUndefined behavior
B42
CEOF
DIt depends on the system
Show answerHide answer
Correct answer: (B) 42
Explanation
The first fscanf reads 42. fseek(file, 0, SEEK_SET) moves back to the start, so the second fscanf reads 42 again, and 42 is printed.
What is the output of the following code?
#include <stdio.h>
int main() {
for (int i = 1; i <= 3; i++) {
for (int j = 1; j <= i; j++) {
printf("*");
}
printf("\n");
}
return 0;
}
A*
**
***
B***
**
*
C***
***
***
DCompilation Error
Show answerHide answer
Correct answer: (A) *
**
***
Explanation
The outer loop runs i = 1 to 3, and the inner loop prints i stars each time, so the rows are *, ** and ***.
What is the output of the following code?
#include <stdio.h>
void func(void);
int main() {
func(10);
return 0;
}
void func(void)
{
printf("Function called\n");
}
ACompilation error
BCompiles successfully but no output displayed
CPrints 'Function called'
DPrints 'Function not called'
Show answerHide answer
Correct answer: (A) Compilation error
Explanation
func is declared as void func(void), so it takes no arguments. Calling func(10) passes an argument, which the compiler rejects as too many arguments.
What will be the output of the following Java code? public class IfExample {
public static void main(String[] args) {
int number = 10;
if (number > 5) {
System.out.println("Number is greater than 5");
}
}
}
ANumber is less than 5
BCompilation error
CNumber is greater than 5
DNo output
Show answerHide answer
Correct answer: (C) Number is greater than 5
Explanation
number = 10, so number > 5 is true and the if block prints "Number is greater than 5".
In C, which of the following file opening modes allow both reading and appending data in a
file?
A"w+"
B"a"
C"r"
D"a+"
Show answerHide answer
Correct answer: (D) "a+"
Explanation
Mode "a+" opens a file for reading and appending: you can read anywhere, and every write goes to the end. "a" only appends, and "w+" truncates the file first.
Consider the following pseudo code.
exponentiate(int x, int n)
{
int m=n; power= 1; z= x;
while(m>0)
{
while(m%2 ==0)
{ m= m/2; z= z*z ;
}
m=m-1; power = power*z;
}
return power;
}
What will the time complexity of function exponentiate() be?
AΘ(n²)
BΘ(log n)
CΘ(n log n)
DΘ(n)
Show answerHide answer
Correct answer: (B) Θ(log n)
Explanation
This is exponentiation by squaring: each inner step halves m, and each outer step subtracts 1 from an odd m, making it even. So m reaches 0 in about 2 log₂ n steps, giving Θ(log n).
Which of the following statements about the DOM (Document Object Model) in JavaScript is
true regarding its interaction with HTML and JavaScript?
AThe DOM only allows reading the HTML document but does not permit any changes or
updates.
BThe DOM allows JavaScript to directly modify the structure of the HTML document by
manipulating its elements, attributes and content.
CThe DOM is a static representation of the page and does not update dynamically when
changes occur in the document.
DThe DOM can only interact with text-based HTML documents and cannot modify styles
or events.
Show answerHide answer
Correct answer: (B) The DOM allows JavaScript to directly modify the structure of the HTML document by
manipulating its elements, attributes and content.
Explanation
The DOM is a live tree of the page. JavaScript can use it to add, remove or change elements, attributes, content, styles and events, and the page updates immediately.
Consider the given memory representation of the singly linked list where start points to the address of first node of the linked list, which is memory location 0.
Memory representation of the singly linked list
Memory location | Item value | Pointer to next element
0 | A | 4
1 | E | 2
2 | B | NULL
3 | |
4 | C | 1
If a new node whose data value is X is inserted after the node whose data value is E in any free location available in the memory, then what will the memory representation be after inserting the new node?
AMemory representation of the linked list after inserting node X
Memory location | Item value | Pointer to next element
0 | A | 4
1 | E | 2
2 | B | NULL
3 | X | 1
4 | C | 3
BMemory representation of the linked list after inserting node X
Memory location | Item value | Pointer to next element
0 | A | 4
1 | E | 3
2 | B | NULL
3 | X | 2
4 | C | 1
CMemory representation of the linked list after inserting node X
Memory location | Item value | Pointer to next element
0 | A | 3
1 | E | 2
2 | B | NULL
3 | X | 4
4 | C | 1
DMemory representation of the linked list after inserting node X
Memory location | Item value | Pointer to next element
0 | A | 4
1 | E | 2
2 | B | 3
3 | X | NULL
4 | C | 1
Show answerHide answer
Correct answer: (B) Memory representation of the linked list after inserting node X
Memory location | Item value | Pointer to next element
0 | A | 4
1 | E | 3
2 | B | NULL
3 | X | 2
4 | C | 1
Explanation
The list is A(0) → C(4) → E(1) → B(2). X goes into free location 3. E's pointer changes to 3, and X points to B at 2, giving A → C → E → X → B as in option B.
What device is primarily used to capture video in multimedia applications?
AMouse
BWebcam
CJoystick
DKeyboard
Show answerHide answer
Correct answer: (B) Webcam
Explanation
A webcam is a video camera connected to a computer and is used to capture live video. A mouse, joystick and keyboard are input devices for control or text.
In the switch control statement of the C program, the control falls through all the cases
unless the _______ statement is given or the end of the switch block is reached.
Acontinue
Bbreak
Cfor
Dreturn
Show answerHide answer
Correct answer: (B) break
Explanation
Without break, control falls through into the following cases until a break or the end of the switch. continue applies only to loops.
What will be the output of the following JavaScript code?
const email = "example@domain";
const regex = /^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}$/;
console.log(regex.test(email));
AError: Invalid regex
Bundefined
CFALSE
DTRUE
Show answerHide answer
Correct answer: (C) FALSE
Explanation
The regex needs a dot and a 2-4 letter top-level domain after the @ part. "example@domain" has no ".com"-style ending, so test() returns false.
Which of the following is the correct way to define a function in Java?
Apublic void myFunction() {}
Bfunction myFunction() {}
Cdef myFunction() {}
DPublic myFunction() {}
Show answerHide answer
Correct answer: (A) public void myFunction() {}
Explanation
In Java a method needs a return type, as in public void myFunction() {}. "function" is JavaScript syntax, "def" is Python, and "Public" (capital P) with no return type is invalid.
What will be the output of the following C program?
#include <stdio.h>
int main()
{
int i = 1;
do
{
printf("%d ", i);
i++;
} while (i <= 5);
return 0;
}
AInfinite Loop
B1 2 3 4 5 6
C1 2 3 4 5
D2 3 4 5 6
Show answerHide answer
Correct answer: (C) 1 2 3 4 5
Explanation
The do-while prints i and then increments it while i <= 5, so it prints 1 2 3 4 5 and stops when i becomes 6.
Which of the following options is INCORRECT about randomised algorithms?
ARandomised algorithms that always produce the same(correct)output for the same
input is known as Las Vegas Algorithms.
BRandomised algorithms whose output differs from run to run for the same inputs is
known as Monte Carlo Algorithms.
CThe execution time of Las Vegas Algorithm does not depend on the output of the
randomiser.
DA randomised algorithm is an algorithm in which some of the decisions made in the
algorithm depend on the output of the randomiser.
Show answerHide answer
Correct answer: (C) The execution time of Las Vegas Algorithm does not depend on the output of the
randomiser.
Explanation
Statement C is incorrect: a Las Vegas algorithm always gives the correct answer, but its running time depends on the random choices. A Monte Carlo algorithm has bounded time, but its output may vary or be wrong.
How to use these DSSSB TGT / PGT Computer Science questions
Every question here was asked in a real DSSSB TGT / PGT paper; the paper and shift are shown on the card, and the number opens the question on its own page. Try each one before tapping Show answer, then attempt the full DSSSB TGT / PGT papers as timed tests to check your speed under exam conditions.