Stacks

Question 1

Which structure allows you to reverse a string by pushing each character and then popping them sequentially?

A. Recursion
B. Array
C. Queue
D. Stack

Answer 1

D. Stack

Question 2

What happens when you push to a full stack?

A. Returns -999
B. Throws exception
C. Stack expands
D. Clears stack

Answer 2

B. Throws exception

Question 3

Which of the following is not a valid stack operation?

A. Peek
B. Push
C. Sort
D. Pop

Answer 3

C. Sort

Question 4

Which of the following is a postfix expression?

A. + A B
B. A B +
C. A * (B + C)
D. A + B

Answer 4

B. A B +

Question 5

Which method checks if the stack is empty?

A. peek
B. isFull
C. clear
D. isEmpty

Answer 5

D. isEmpty

Question 6

What is the result of popping all elements from a stack?

A. Empty stack
B. Overflow
C. Segmentation fault
D. Full stack

Answer 6

A. Empty stack

Question 7

Which operation removes the top item from the stack?

A. delete
B. peek
C. remove
D. pop

Answer 7

D. pop

Question 8

Which data structure is used to reverse a string using stack logic?

A. Tree
B. Graph
C. Queue
D. Stack

Answer 8

D. Stack

Question 9

What does the term LIFO stand for in stack operations?

A. Least Important First Out
B. Last Item First Out
C. Last In First Out
D. Last In Fast Out

Answer 9

C. Last In First Out

Question 10

What is the time complexity of push and pop operations in a stack?

A. O(n)
B. O(log n)
C. O(1)
D. O(n²)

Answer 10

C. O(1)

Question 11

What is the default top value when a new stack is created?

A. 0
B. null
C. -1
D. 1

Answer 11

C. -1

Question 12

Which application uses stacks?

A. Hashing
B. Breadth-first search
C. Priority queue
D. Undo feature

Answer 12

D. Undo feature

Question 13

Which of the following is true about postfix notation?

A. Operators come before operands
B. Operators come after operands
C. It’s ambiguous
D. Parentheses are required

Answer 13

B. Operators come after operands

Question 14

Which of the following is true about stack ADT?

A. It allows random access
B. It has fixed size
C. It follows FIFO
D. It allows access only to the top

Answer 14

D. It allows access only to the top

Question 15

What is the result of peek() on an empty stack?

A. null
B. -999
C. 0
D. top

Answer 15

A. null

Question 16

Which Java class is used for predefined stack operations?

A. java.util.Array
B. java.util.List
C. java.util.Stack
D. java.util.Queue

Answer 16

C. java.util.Stack

Question 17

What does the peek operation do in a stack?

A. Removes top
B. Views top
C. Clears stack
D. Adds top

Answer 17

B. Views top

Question 18

Which data structure is typically used to implement a stack?

A. Queue
B. Array
C. Tree
D. Graph

Answer 18

B. Array

Question 19

Which of the following is NOT a valid stack operation?

A. peek
B. push
C. delete
D. pop

Answer 19

C. delete

Question 20

Which operation adds an item to the top of the stack?

A. pop
B. peek
C. insert
D. push

Answer 20

D. push

Question 21

Which of the following is true about stack in system memory?

A. It stores static data
B. It stores heap
C. It stores global variables
D. It stores function calls

Answer 21

D. It stores function calls

Question 22

In which of the following scenarios would the use of multiple stacks be a valid and common approach?

A. Binary Search
B. Expression Conversion and Evaluation
C. Hashing
D. Bubble Sort

Answer 22

B. Expression Conversion and Evaluation

Question 23

What is the output of pushing 1, 2, 3 and popping once?

A. 3
B. 1
C. 0
D. 2

Answer 23

A. 3

Question 24

Which of the following is true about linked list-based stack?

A. Dynamic size
B. Fixed size
C. Slower than array
D. Requires sorting

Answer 24

A. Dynamic size

Question 25

Which condition causes stack overflow? A. Pushing into full stack B. Peeking top C. Reversing stack D. Popping from empty stack

Answer 25

A. Pushing into full stack

Question 26

What is the result of evaluating the prefix expression + 5 * 3 2? A. 10 B. 13 C. 16 D. 11

Answer 26

D. 11

Question 27

Which of the following is the correct order of operations in postfix evaluation? A. Right to left B. Left to right C. Top to bottom D. Bottom to top

Answer 27

B. Left to right

Question 28

Which of the following best describes stack ADT? A. Linear, restricted access B. Non-linear, random access C. Linear, dynamic access D. Circular, indexed access

Answer 28

A. Linear, restricted access

Question 29

What is the role of stack in recursion? A. Stores function calls B. Stores variables C. Stores loops D. Stores return values

Answer 29

A. Stores function calls

Question 30

What is the result of evaluating the postfix expression 5 3 + 2 *? A. 10 B. 11 C. 16 D. 13

Answer 30

C. 16

Question 31

Which expression evaluation uses stacks? A. Prefix B. Infix C. Postfix D. All of the above

Answer 31

D. All of the above

Question 32

What is the result of evaluating the postfix expression 6 2 / 3 -? A. 3 B. 2 C. 0 D. 1

Answer 32

C. 0

Question 33

Which of the following is not a valid postfix expression? A. AB+ B. A+BC+ C. ABC+* D. AB+C*

Answer 33

B. A+BC+

Question 34

What is the main drawback of array-based stack implementation? A. Complex syntax B. Fixed size C. Slow access D. Memory overflow

Answer 34

B. Fixed size

Question 35

Which of the following is true about stack ADT in Java? A. Stack is an interface B. Stack is abstract C. Stack is a class D. Stack is deprecated

Answer 35

C. Stack is a class