Pop Operation on Stack in DSA C# - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to remove the top element from the stack.

DSA C#

stack.[1]();

Drag options to blanks, or click blank then click option'

AClear

BPush

CPeek

DPop

Attempts:

3 left

💡 Hint

Common Mistakes

Using Push instead of Pop will add an element instead of removing.

Using Peek only looks at the top element without removing it.

The Pop method removes and returns the top element of the stack.

2fill in blank

medium

Complete the code to check if the stack is empty before popping.

DSA C#

if (stack.[1] > 0) { stack.Pop(); }

Drag options to blanks, or click blank then click option'

ACount

BCapacity

CSize

DLength

Attempts:

3 left

💡 Hint

Common Mistakes

Using Length or Size which are not properties of Stack in C#.

Using Capacity which is about internal storage, not current count.

The Count property gives the number of elements in the stack.

3fill in blank

hard

Fix the error in the code to correctly pop and store the top element.

DSA C#

int top = stack.[1]();

Drag options to blanks, or click blank then click option'

APop

BPeek

CPush

DRemove

Attempts:

3 left

💡 Hint

Common Mistakes

Using Peek which does not remove the element.

Using Push or Remove which are not valid methods for this purpose.

Pop removes and returns the top element, so it can be stored in a variable.

4fill in blank

hard

Fill both blanks to pop all elements from the stack until it is empty.

DSA C#

while (stack.[1] > 0) { var item = stack.[2](); }

Drag options to blanks, or click blank then click option'

ACount

BPop

CPeek

DLength

Attempts:

3 left

💡 Hint

Common Mistakes

Using Peek instead of Pop to remove items.

Using Length which is not a Stack property.

Use Count to check if stack has elements and Pop to remove them one by one.

5fill in blank

hard

Fill all three blanks to pop elements and print them until the stack is empty.

DSA C#

while (stack.[1] > 0) {
    int [2] = stack.[3]();
    Console.WriteLine([2]);
}

Drag options to blanks, or click blank then click option'

ACount

Btop

CPop

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect variable names.

Using Peek instead of Pop.

Use Count to check stack size, Pop to remove top element, and store it in variable top to print.

Practice

1. What does the Pop() operation do in a stack?

easy

A. Adds an element to the bottom of the stack

B. Clears all elements from the stack

C. Returns the bottom element without removing it

D. Removes and returns the top element of the stack

Solution

1. Step 1: Understand the stack behavior

   A stack follows Last In First Out (LIFO) principle, so the last added element is on top.

2. Step 2: Define the Pop operation

   Pop removes and returns the top element, which is the last inserted item.

3. Final Answer:

   Removes and returns the top element of the stack -> Option D

4. Quick Check:

   Pop = remove top element [OK]

Hint: Pop always removes the last added item [OK]

Common Mistakes:

• Thinking Pop adds elements
• Confusing Pop with Peek
• Assuming Pop removes bottom element

2. Which of the following is the correct syntax to pop an element from a stack named myStack in C#?

easy

A. myStack.Pop();

B. myStack.pop();

C. Pop(myStack);

D. myStack.PopElement();

Solution

1. Step 1: Recall C# method naming conventions

   In C#, method names are case-sensitive and usually PascalCase.

2. Step 2: Identify the correct method call

   The Stack class has a method named Pop() with uppercase P, called on the stack instance.

3. Final Answer:

   myStack.Pop(); -> Option A

4. Quick Check:

   Correct method name and syntax = myStack.Pop(); [OK]

Hint: C# methods are case-sensitive and PascalCase [OK]

Common Mistakes:

• Using lowercase 'pop()' instead of 'Pop()'
• Trying to call Pop as a standalone function
• Using incorrect method names like PopElement

3. What will be the output of the following C# code?

Stack<int> stack = new Stack<int>();
stack.Push(10);
stack.Push(20);
stack.Push(30);
int popped = stack.Pop();
Console.WriteLine(popped);
Console.WriteLine(string.Join(", ", stack));

medium

A. 10
20, 30

B. 30
20, 10

C. 20
10, 30

D. 30
10, 20

Solution

1. Step 1: Trace the Push operations

   Elements pushed in order: 10 (bottom), 20, 30 (top).

2. Step 2: Pop removes top element

   Pop removes 30, so popped = 30. Remaining stack: 20 (top), 10 (bottom).

3. Step 3: Print statements

   First line prints popped = 30. Second line prints stack elements from top to bottom: 20, 10.

4. Final Answer:

   30 20, 10 -> Option B

5. Quick Check:

   Pop returns top (30), stack now 20, 10 [OK]

Hint: Pop returns last pushed; stack order reverses on print [OK]

Common Mistakes:

• Confusing order of elements after pop
• Printing stack in wrong order
• Assuming Pop returns bottom element

4. Identify the error in the following C# code snippet that uses a stack:

Stack<string> stack = new Stack<string>();
stack.Push("apple");
stack.Push("banana");
string fruit = stack.Pop();
Console.WriteLine(fruit);
Console.WriteLine(stack.Pop());
Console.WriteLine(stack.Pop());

medium

A. Pop method is called incorrectly

B. No error, code runs fine

C. Third Pop causes InvalidOperationException (stack empty)

D. Stack should be initialized with capacity

Solution

1. Step 1: Count Push and Pop calls

   Two Push calls add "apple" and "banana". Three Pop calls remove elements.

2. Step 2: Analyze stack state after Pops

   First Pop removes "banana", second Pop removes "apple", third Pop tries to remove from empty stack causing error.

3. Final Answer:

   Third Pop causes InvalidOperationException (stack empty) -> Option C

4. Quick Check:

   Pop on empty stack throws exception [OK]

Hint: Pop more times than Push causes error [OK]

Common Mistakes:

• Ignoring stack empty error
• Assuming Pop returns null if empty
• Thinking stack needs capacity on init

5. Given a stack with elements [5, 10, 15, 20] (5 at bottom, 20 at top), what will be the stack content after performing two Pop() operations followed by one Push(25) operation?

hard

A. [5, 10, 25]

B. [5, 10, 15, 25]

C. [10, 15, 25]

D. [5, 15, 25]

Solution

1. Step 1: Understand initial stack order

   Stack bottom to top: 5, 10, 15, 20.

2. Step 2: Perform two Pop operations

   First Pop removes 20, second Pop removes 15. Remaining stack: 5, 10.

3. Step 3: Perform Push(25)

   Push adds 25 on top. Final stack: 5, 10, 25.

4. Final Answer:

   [5, 10, 25] -> Option A

5. Quick Check:

   Pop twice removes top two; Push adds new top [OK]

Hint: Pop removes top; Push adds new top [OK]

Common Mistakes:

• Removing wrong elements on Pop
• Adding Push element at bottom
• Confusing stack order after operations