Push Operation on Stack in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push an element onto the stack.

DSA C++

stack.push([1]);

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

Avalue

Bpop()

Cempty()

Dtop()

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() instead of the value to push.

Calling top() which only returns the top element.

Using empty() which checks if the stack is empty.

The push operation adds the given value to the top of the stack.

2fill in blank

medium

Complete the code to declare a stack of integers.

DSA C++

std::stack<[1]> stack;

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

Astring

Bfloat

Cint

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Using float or string instead of int.

Confusing bool with int.

The stack is declared to hold integers using std::stack.

3fill in blank

hard

Fix the error in the push operation code.

DSA C++

stack.[1](10);

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

Apush

Bpop

Ctop

Dempty

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() which removes elements.

Using top() which only accesses the top element.

Using empty() which checks if stack is empty.

The correct method to add an element is push, not pop or top.

4fill in blank

hard

Fill both blanks to create a stack and push a value 5.

DSA C++

std::stack<[1]> stack;
stack.[2](5);

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

Aint

Bpush

Cpop

Dfloat

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of push.

Using float instead of int.

Declare stack of int and use push to add 5.

5fill in blank

hard

Fill all three blanks to push the top element's value plus 1 onto the stack.

DSA C++

int topValue = stack.[1]();
stack.[2](topValue [3] 1);

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

Atop

Bpush

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() instead of top().

Using - instead of +.

Using pop() instead of push() to add.

Use top() to get the top element, push() to add, and + to add 1.

Practice

1. What does the push operation do in a stack?

easy

A. Checks if the stack is empty

B. Removes the top element from the stack

C. Returns the bottom element of the stack

D. Adds an element to the top of the stack

Solution

1. Step 1: Understand stack behavior

   A stack follows Last In First Out (LIFO) principle, where elements are added or removed from the top.

2. Step 2: Define push operation

   The push operation adds a new element on top of the existing stack elements.

3. Final Answer:

   Adds an element to the top of the stack -> Option D

4. Quick Check:

   Push = Add top element [OK]

Hint: Push means add element on top of stack [OK]

Common Mistakes:

• Confusing push with pop operation
• Thinking push removes elements
• Assuming push checks stack emptiness

2. Which of the following is the correct syntax to push an integer 10 onto a stack named stk in C++ STL?

easy

A. stk.push(10);

B. stk.add(10);

C. stk.insert(10);

D. stk.append(10);

Solution

1. Step 1: Recall C++ STL stack methods

   The standard method to add an element to a stack is push().

2. Step 2: Match correct syntax

   Using stk.push(10); correctly pushes 10 onto the stack.

3. Final Answer:

   stk.push(10); -> Option A

4. Quick Check:

   push() is the correct method [OK]

Hint: Use push() to add elements in C++ stack [OK]

Common Mistakes:

• Using add(), insert(), or append() which are not stack methods
• Forgetting parentheses after push
• Confusing vector methods with stack

3. What will be the output after executing the following C++ code?

std::stack<int> stk;
stk.push(5);
stk.push(10);
stk.push(15);
int topElement = stk.top();

What is the value of topElement?

medium

A. 15

B. 10

C. 0

D. 5

Solution

1. Step 1: Trace push operations

   Elements pushed in order: 5, then 10, then 15. Stack top is last pushed element.

2. Step 2: Identify top element

   The top element after pushes is 15, as it was pushed last.

3. Final Answer:

   15 -> Option A

4. Quick Check:

   Last pushed = top element = 15 [OK]

Hint: Top element is last pushed value [OK]

Common Mistakes:

• Choosing first pushed element as top
• Confusing top() with pop()
• Assuming stack is empty initially

4. Identify the error in the following code snippet that tries to push an element onto a stack:

std::stack<int> stk;
stk.push 20;

medium

A. Using wrong data type for stack

B. Stack not declared properly

C. Missing parentheses in push call

D. No error in the code

Solution

1. Step 1: Check push syntax

   The push method requires parentheses around the argument, like push(20).

2. Step 2: Identify syntax error

   Code uses stk.push 20; missing parentheses, causing a syntax error.

3. Final Answer:

   Missing parentheses in push call -> Option C

4. Quick Check:

   push() needs parentheses [OK]

Hint: Always use parentheses with push() [OK]

Common Mistakes:

• Omitting parentheses after push
• Confusing push with pop syntax
• Assuming stack declaration is wrong

5. Given an empty stack, what will be the state of the stack after executing the following code?

std::stack<int> stk;
stk.push(1);
stk.push(2);
stk.push(3);
stk.pop();
stk.push(4);

Choose the correct sequence of elements from top to bottom.

hard

A. 3 -> 2 -> 1 -> null

B. 4 -> 2 -> 1 -> null

C. 1 -> 2 -> 4 -> null

D. 2 -> 4 -> 1 -> null

Solution

1. Step 1: Trace push and pop operations

   Push 1, stack: 1
   Push 2, stack: 2 -> 1
   Push 3, stack: 3 -> 2 -> 1
   Pop removes top (3), stack: 2 -> 1
   Push 4, stack: 4 -> 2 -> 1

2. Step 2: Write final stack state

   Top to bottom: 4 -> 2 -> 1 -> null

3. Final Answer:

   4 -> 2 -> 1 -> null -> Option B

4. Quick Check:

   Push/pop order = 4,2,1 [OK]

Hint: Pop removes top; next push adds new top [OK]

Common Mistakes:

• Ignoring pop effect on stack
• Assuming push adds at bottom
• Mixing order of elements after pop