In Data Structures, Queue & Circular Queue are repeatedly asked topics in ECET exams. Questions test the understanding of operations, differences, and applications.
📘 Concept Notes
🌍 What is a Queue?
- A Queue is a linear data structure that follows the FIFO (First In First Out) principle.
- Example: People standing in a ticket queue – first person in is served first.
⚙️ Basic Queue Operations
- Enqueue (Insertion) – Insert an element at the rear end.
- Dequeue (Deletion) – Remove an element from the front end.
- Peek/Front – Retrieve the element at front without deleting.
- isEmpty() – Checks if the queue is empty.
- isFull() – Checks if the queue is full (array implementation).
🔄 Limitation of Linear Queue
- In a simple array queue, after several enqueues and dequeues, unused spaces cannot be reused.
- Example: If size = 5, after inserting 5 and deleting 3, we still cannot insert more (overflow occurs) because rear pointer has reached the end.
🌐 Circular Queue
- A Circular Queue overcomes the limitation of linear queues.
- Here, the last position is connected back to the first position.
- Elements can be inserted at rear and removed from front in a circular way.
Formulas (using array of size N):
- Enqueue Condition: Queue is full when
Dequeue Condition: Queue is empty when
After First Insertion:
Enqueue Operation:
Dequeue Operation:
📊 Example – Circular Queue of size 5
- Enqueue: 10 → 20 → 30 → 40 → 50
- Dequeue: Remove 10, 20
- Enqueue: 60, 70 → They occupy positions of freed spaces (circularly).
🔟 10 Expected MCQs – ECET 2026
Q1. A Queue works on which principle?
A) LIFO
B) FIFO
C) FILO
D) Random
Q2. In linear queue, insertion is done at:
A) Front
B) Rear
C) Middle
D) Both ends
Q3. In queue, deletion is performed from:
A) Rear
B) Front
C) Any position
D) None
Q4. Which problem occurs in a simple array queue?
A) Overflow
B) Underflow
C) Wasted space
D) All of the above
Q5. Which queue connects last position back to first position?
A) Simple Queue
B) Priority Queue
C) Circular Queue
D) Deque
Q6. In a circular queue of size N, the condition for full is:
A) rear = N – 1
B) (rear + 1) % N = front
C) rear = front
D) front = –1
Q7. In circular queue, after deletion if queue becomes empty:
A) front = 0, rear = 0
B) front = rear = –1
C) rear = N – 1
D) None
Q8. Which queue allows insertion at rear and deletion at front?
A) Deque
B) Simple Queue
C) Circular Queue
D) Both B & C
Q9. In enqueue operation of circular queue, rear is updated as:
A) rear = rear + 1
B) rear = (rear + 1) % N
C) rear = front + 1
D) None
Q10. Circular queue is useful to:
A) Utilize memory efficiently
B) Increase complexity
C) Avoid dynamic allocation
D) Reduce time complexity
✅ Answer Key
| Q.No | Answer |
|---|---|
| Q1 | B |
| Q2 | B |
| Q3 | B |
| Q4 | D |
| Q5 | C |
| Q6 | B |
| Q7 | B |
| Q8 | D |
| Q9 | B |
| Q10 | A |
🧠 Explanations
- Q1 → B: Queue works on FIFO principle.
- Q2 → B: Insertion at rear end.
- Q3 → B: Deletion from front end.
- Q4 → D: Overflow, underflow, and wasted space all occur in linear queues.
- Q5 → C: Circular Queue connects last → first.
- Q6 → B: Formula for full: (rear+1)%N = front.
- Q7 → B: When queue is empty, front & rear reset to –1.
- Q8 → D: Both Simple and Circular queues allow this.
- Q9 → B: Rear moves circularly.
- Q10 → A: Circular queues efficiently utilize memory.
🎯 Why Practice Matters
Queues & Circular Queues are frequently tested in ECET CSE/IT Data Structures section. Most MCQs are direct formula/definition based. Understanding operations and formulas ensures 2–3 marks guaranteed.
