Stack Concept and LIFO Principle in DSA C - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this stack push and pop sequence?

Consider a stack initially empty. We perform these operations in order:
push(5), push(10), pop(), push(15), pop(), pop().
What is the output of each pop operation?

DSA C

Stack operations:
push(5)
push(10)
pop() -> ?
push(15)
pop() -> ?
pop() -> ?

A [10, 15, 5]

B [5, 10, 15]

C [15, 10, 5]

D [5, 15, 10]

💡 Hint

Remember stack follows Last In First Out (LIFO). The last pushed item is popped first.

The first pop removes 10 (last pushed), second pop removes 15, third pop removes 5.

🧠 Conceptual

intermediate

Which statement correctly describes the LIFO principle in stacks?

Choose the statement that best explains how the LIFO principle works in a stack.

A The first element added is the first one to be removed.

B Elements are removed in the reverse order they were added.

C The last element added is the last one to be removed.

D Elements are removed randomly regardless of insertion order.

💡 Hint

Think about which element is on top of the stack.

LIFO means last in, first out, so the last element added is removed first.

🔧 Debug

advanced

What error occurs in this stack pop implementation?

Given this C code snippet for popping from a stack, what error will occur if the stack is empty?

int pop() {
  if (top == -1) {
    return stack[top];
  }
  return stack[top--];
}

DSA C

int pop() {
  if (top == -1) {
    return stack[top];
  }
  return stack[top--];
}

A No error, works fine

B Stack underflow error handled correctly

C Syntax error due to missing braces

D Returns garbage value from invalid index

💡 Hint

Check what happens when top is -1 and you access stack[top].

When top is -1, accessing stack[-1] is invalid and returns garbage or causes runtime error.

📝 Syntax

advanced

Which option correctly declares a stack array and top variable in C?

Choose the correct C code snippet to declare a stack of size 10 and initialize top to -1.

A int stack[10]; int top = -1;

B int stack; int top = 0;

C int stack[10]; int top = 0;

D int stack[] = 10; int top = -1;

💡 Hint

Stack is an array, top starts at -1 to indicate empty stack.

Option A correctly declares an integer array and initializes top to -1.

🚀 Application

expert

After these stack operations, what is the stack content?

Start with an empty stack. Perform:
push(1), push(2), push(3), pop(), push(4), pop(), push(5).
What is the final stack content from bottom to top?

A 1 -> 3 -> 5 -> null

B 1 -> 4 -> 5 -> null

C 1 -> 2 -> 5 -> null

D 2 -> 4 -> 5 -> null

💡 Hint

Track each push and pop carefully, remembering LIFO order.

Pop removes 3, then pop removes 4, so stack ends with 1, 2, 5.