Queues MCQs – T4Tutorials.com

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1. What is a queue?
(A) A linear data structure that follows the Last In First Out (LIFO) principle
(B) A linear data structure that follows the First In First Out (FIFO) principle
(C) A non-linear data structure
(D) A type of stack

2. Which operation adds an element to the end of a queue?
(A) Enqueue
(B) Dequeue
(C) Push
(D) Pop

3. Which operation removes an element from the front of a queue?
(A) Enqueue
(B) Dequeue
(C) Push
(D) Pop

4. What is the time complexity for the enqueue operation in a queue?
(A) O(1)
(B) O(n)
(C) O(log n)
(D) O(n log n)

5. What is the time complexity for the dequeue operation in a queue?
(A) O(1)
(B) O(n)
(C) O(log n)
(D) O(n log n)

6. What is the main disadvantage of using an array to implement a queue?
(A) Fixed size
(B) Slow access
(C) Complexity in implementation
(D) None of the above

7. Which of the following is true about a queue?
(A) Elements can be accessed in any order
(B) The first element added is the first to be removed
(C) It supports random access
(D) It is a non-linear data structure

8. What happens when you try to dequeue from an empty queue?
(A) It returns NULL
(B) It causes an underflow error
(C) It returns zero
(D) It does nothing

9. What is the primary use of queues in programming?
(A) Implementing stacks
(B) Managing requests in order
(C) Sorting data
(D) Storing data in arrays

10. Which of the following operations is NOT supported by a queue?
(A) Enqueue
(B) Dequeue
(C) Peek
(D) Push

11. What does the front operation do in a queue?
(A) Adds an element to the queue
(B) Removes the front element from the queue
(C) Returns the front element without removing it
(D) Clears the queue

12. How is a queue typically represented in memory?
(A) Using arrays only
(B) Using linked lists only
(C) Using both arrays and linked lists
(D) Using trees

13. What happens to the front pointer when an element is enqueued?
(A) It moves up
(B) It moves down
(C) It remains unchanged
(D) It points to NULL

14. What is the maximum size of a queue implemented using an array?
(A) Dynamic, can grow indefinitely
(B) Limited by the memory available
(C) Fixed at the time of declaration
(D) Depends on the programming language

15. What is the primary characteristic of a circular queue?
(A) It can grow and shrink dynamically
(B) The last element points to the first element
(C) It requires more memory than a regular queue
(D) It cannot store more than one element

16. Which of the following scenarios can be solved using a queue?
(A) Managing print jobs
(B) Reversing a string
(C) Depth-first search in graphs
(D) All of the above

17. In which data structure do you use a queue for breadth-first search?
(A) Stack
(B) Array
(C) Linked List
(D) Graph

18. What is the output of the following code if the queue is empty? queue.dequeue();
(A) It removes the last element
(B) It returns NULL
(C) It throws an error
(D) It does nothing

19. What is a common application of queues?
(A) Undo functionality in applications
(B) Storing data in arrays
(C) Scheduling tasks
(D) Implementing a binary search

20. How do you implement a queue using two stacks?
(A) By using one stack for enqueue and the other for dequeue
(B) By using one stack for storing elements and the other for reversing the order
(C) By interleaving the two stacks
(D) It cannot be done

21. Which of the following describes a queue’s memory allocation?
(A) Queues use dynamic memory allocation only
(B) Queues can use both static and dynamic memory allocation
(C) Queues use fixed memory allocation only
(D) Queues do not require memory allocation

22. What is the difference between a queue and a stack?
(A) Stacks use FIFO while queues use LIFO
(B) Queues use FIFO while stacks use LIFO
(C) Both are the same
(D) Queues require more memory

23. Which of the following can cause a queue overflow?
(A) Using too much memory
(B) Enqueuing elements into a full queue
(C) Dequeuing elements from an empty queue
(D) Both B and C

24. What is the effect of using delete on a queue node in C++?
(A) It frees the memory allocated for that node
(B) It only removes the data
(C) It causes a memory leak
(D) It does nothing

25. What is the time complexity for finding the size of a queue?
(A) O(1)
(B) O(n)
(C) O(log n)
(D) O(n log n)

26. Which data structure can be used to implement a priority queue?
(A) Stack
(B) Queue
(C) Array
(D) All of the above

27. What is the main difference between a queue and a deque (double-ended queue)?
(A) A queue allows insertion and deletion at both ends
(B) A deque allows insertion and deletion at both ends
(C) A queue allows random access
(D) A deque is more complex

28. What is the time complexity for checking if a queue is empty?
(A) O(1)
(B) O(n)
(C) O(log n)
(D) O(n log n)

29. In a circular queue, what happens when the rear pointer reaches the end of the array?
(A) It points to NULL
(B) It wraps around to the front of the array
(C) It causes an overflow
(D) It becomes undefined

30. Which of the following is NOT a characteristic of queues?
(A) FIFO order
(B) Random access
(C) Linear structure
(D) Can be implemented using arrays or linked lists

31. What type of queue is used in breadth-first search?
(A) Circular queue
(B) Double-ended queue
(C) Regular queue
(D) Priority queue

32. What is the purpose of the rear pointer in a queue?
(A) To point to the front element
(B) To point to the last added element
(C) To keep track of the size
(D) To remove elements

33. How can you implement a circular queue?
(A) By using two pointers and wrapping them around
(B) By using a fixed-size array
(C) By using a linked list
(D) Both A and B

34. Which of the following operations can be performed in a priority queue?
(A) Insert with priority
(B) Remove the highest priority element
(C) Peek at the highest priority element
(D) All of the above

35. What is the output of the following code if the queue is full? queue.enqueue(5);
(A) It adds the element
(B) It throws an overflow error
(C) It ignores the element
(D) It returns NULL

36. What is a common use of a queue in operating systems?
(A) To manage memory
(B) To handle task scheduling
(C) To sort data
(D) To implement recursion

37. What is the primary characteristic of a double-ended queue (deque)?
(A) It allows insertion and deletion at both ends
(B) It allows random access
(C) It follows FIFO order
(D) It is more complex than a regular queue

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By: Prof. Dr. Fazal Rehman | Last updated: May 14, 2025

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