Queue vs Stack When to Use Which in DSA C - Compare & Choose

Challenge - 5 Problems

🧠 Conceptual

intermediate

Choosing Between Queue and Stack for Task Scheduling

You have a list of tasks that must be processed in the exact order they arrive. Which data structure is best to use?

A Stack, because it processes the most recent task first.

B Queue, because it processes tasks in reverse order.

C Stack, because it allows random access to tasks.

D Queue, because it processes tasks in the order they arrive.

💡 Hint

Think about which data structure follows the 'first come, first served' rule.

A queue processes elements in the order they arrive (FIFO), which is perfect for task scheduling where order matters. A stack processes elements in reverse order (LIFO), which is not suitable here.

❓ Predict Output

intermediate

Output of Stack Operations

What is the printed output after executing the following stack operations?

DSA C

Stack s = create_stack();
push(s, 10);
push(s, 20);
push(s, 30);
int x = pop(s);
print(x);
int y = pop(s);
print(y);

A

30
20

B

10
20

C

20
30

D

10
30

💡 Hint

Remember that stack removes the last pushed item first.

Stack is LIFO. The last pushed item is 30, so pop returns 30 first, then 20.

❓ Predict Output

advanced

Queue Behavior with Enqueue and Dequeue

What is the state of the queue after these operations?

DSA C

Queue q = create_queue();
enqueue(q, 5);
enqueue(q, 10);
dequeue(q);
enqueue(q, 15);
print_queue(q);

A 5 -> 10 -> 15 -> null

B 10 -> 15 -> null

C 15 -> 10 -> null

D 5 -> 15 -> null

💡 Hint

Remember that dequeue removes from the front of the queue.

After enqueue 5 and 10, queue is 5 -> 10. Dequeue removes 5. Then enqueue 15 adds to the end. Final queue is 10 -> 15.

🔧 Debug

advanced

Identifying Error in Stack Usage

What error will this code produce?

DSA C

Stack s = create_stack();
push(s, 1);
pop(s);
pop(s);

A Underflow error because pop is called on empty stack.

B Overflow error because stack is full.

C No error, returns 1 then 0.

D Syntax error due to missing semicolon.

💡 Hint

Think about what happens when you pop more times than you push.

After popping once, the stack is empty. Popping again causes underflow error because there is nothing to pop.

🧠 Conceptual

expert

Choosing Data Structure for Undo Feature

You are designing an undo feature for a text editor. Which data structure is best suited and why?

A Queue, because it allows random access to previous actions.

B Queue, because it processes actions in the order they were done.

C Stack, because it allows reversing the most recent action first.

D Stack, because it processes actions in the order they were done.

💡 Hint

Undo means reversing the last action first.

An undo feature needs to reverse the most recent action first, which is exactly how a stack works (LIFO). A queue processes in the order actions were done, which is not suitable.