Push Operation on Stack in DSA C++ - Build from Scratch

Push Operation on Stack

📖 Scenario: Imagine you are managing a stack of books. You want to add new books on top of the stack one by one. This project will help you understand how to add (push) items to a stack using C++.

🎯 Goal: You will create a stack using a list, set a maximum size for the stack, write the push operation to add items to the stack, and finally print the stack's content.

📋 What You'll Learn

Create a stack as a list of integers with initial values

Create a variable for the maximum size of the stack

Write a push function to add an integer to the stack if there is space

Print the stack content after pushing a new item

💡 Why This Matters

🌍 Real World

Stacks are used in many real-world applications like undo features in text editors, browser history, and managing function calls in programming.

💼 Career

Understanding stack operations is essential for software developers, especially when working with algorithms, memory management, and system design.

1

Create the initial stack

Create a list called stack with these exact integers: 10, 20, 30

DSA C++

# Create a list called stack with 10, 20, 30
# Your code here

Hint

Use std::vector<int> to create the stack list with the given numbers.

2

Set the maximum stack size

Create an integer variable called max_size and set it to 5

DSA C++

std::vector stack = {10, 20, 30};
// Create max_size variable and set it to 5
# Your code here

Hint

Use int max_size = 5; to set the maximum stack size.

3

Write the push operation

Write a function called push that takes an integer value and adds it to stack only if stack.size() is less than max_size

DSA C++

std::vector stack = {10, 20, 30};
int max_size = 5;

// Write push function below
# Your code here

Hint

Check if stack.size() is less than max_size before adding value to stack.

4

Push a new value and print the stack

Call push(40) to add 40 to the stack, then print the stack elements separated by spaces on one line

DSA C++

std::vector stack = {10, 20, 30};
int max_size = 5;

void push(int value) {
    if (stack.size() < max_size) {
        stack.push_back(value);
    }
}

// Call push(40) and print stack
# Your code here

Hint

Use a for loop to print each element of stack separated by spaces after calling push(40).

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