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.

🎯 Goal: You will create a stack, prepare a new book to add, perform the push operation to add the book on top, and then display the stack.

📋 What You'll Learn

Create a stack of strings called bookStack.

Create a string variable called newBook with the value "Data Structures".

Use the Push method to add newBook to bookStack.

Print the contents of bookStack from top to bottom.

💡 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.

💼 Career

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

1

Create the stack

Create a stack of strings called bookStack.

DSA C#

// Your code here

Hint

Use Stack<string> to create the stack.

2

Create the new book variable

Create a string variable called newBook and set it to "Data Structures".

DSA C#

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        Stack bookStack = new Stack();
        // Your code here
    }
}

Hint

Use string newBook = "Data Structures"; to create the variable.

3

Push the new book onto the stack

Use the Push method to add newBook to bookStack.

DSA C#

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        Stack bookStack = new Stack();
        string newBook = "Data Structures";
        // Your code here
    }
}

Hint

Use bookStack.Push(newBook); to add the book on top.

4

Print the stack contents

Use a foreach loop with variable book to iterate over bookStack and print each book on a new line.

DSA C#

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        Stack bookStack = new Stack();
        string newBook = "Data Structures";
        bookStack.Push(newBook);
        // Your code here
    }
}

Hint

Use foreach (string book in bookStack) and Console.WriteLine(book); to print each book.

Practice

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

easy

A. Adds an element to the top of the stack

B. Removes the top element from the stack

C. Returns the bottom element of the stack

D. Checks if the stack is empty

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 stack, increasing its size by one.

3. Final Answer:

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

4. Quick Check:

   Push = Add top element [OK]

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

Common Mistakes:

• Confusing Push with Pop operation
• Thinking Push removes elements
• Assuming Push accesses bottom element

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

easy

A. stack.Insert(10);

B. stack.Add(10);

C. stack.Push(10);

D. stack.Push = 10;

Solution

1. Step 1: Recall Stack method for adding elements

   In C#, the Stack class uses the method Push() to add elements.

2. Step 2: Check syntax correctness

   The correct syntax is calling Push with the value inside parentheses: stack.Push(10);

3. Final Answer:

   stack.Push(10); -> Option C

4. Quick Check:

   Push method call syntax = stack.Push(value) [OK]

Hint: Use stack.Push(value) to add elements [OK]

Common Mistakes:

• Using Add or Insert which are not stack methods
• Assigning value directly to Push
• Missing parentheses in method call

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

Stack<int> stack = new Stack<int>();
stack.Push(5);
stack.Push(10);
stack.Push(15);
Console.WriteLine(string.Join(", ", stack));

medium

A. 5, 10, 15

B. 15, 10, 5

C. 10, 15, 5

D. 15, 5, 10

Solution

1. Step 1: Understand push order and stack iteration

   Elements pushed are 5, then 10, then 15. Stack stores last pushed on top.

2. Step 2: Determine iteration order when printing

   Stack enumerates from top to bottom, so output order is 15, 10, 5.

3. Final Answer:

   15, 10, 5 -> Option B

4. Quick Check:

   Stack top to bottom = 15, 10, 5 [OK]

Hint: Stack prints top element first [OK]

Common Mistakes:

• Assuming stack prints in push order
• Confusing stack with queue order
• Forgetting stack is LIFO

4. Identify the error in the following C# code that tries to push elements onto a stack:

Stack<string> stack = new Stack<string>();
stack.Push "hello";
stack.Push("world");

medium

A. Push method does not exist

B. Stack cannot hold strings

C. Missing semicolon after second Push

D. Missing parentheses in first Push call

Solution

1. Step 1: Check syntax of Push calls

   The first Push call is written as stack.Push "hello"; missing parentheses.

2. Step 2: Confirm correct method usage

   Push requires parentheses around argument: stack.Push("hello");

3. Final Answer:

   Missing parentheses in first Push call -> Option D

4. Quick Check:

   Method calls need parentheses [OK]

Hint: Always use parentheses with method calls [OK]

Common Mistakes:

• Ignoring parentheses syntax
• Thinking stack can't hold strings
• Assuming missing semicolon causes error here

5. Given a stack initially empty, what will be the content of the stack after executing the following code?

Stack<int> stack = new Stack<int>();
for (int i = 1; i <= 3; i++)
{
    stack.Push(i * 2);
}
stack.Push(10);
stack.Push(stack.Pop() + 5);

hard

A. 15, 6, 4, 2

B. 10, 8, 4, 2

C. 15, 10, 6, 4, 2

D. 10, 15, 6, 4, 2

Solution

1. Step 1: Trace the for loop pushing values

   Loop pushes 2, 4, 6 in order. Stack top is 6, bottom is 2.

2. Step 2: Push 10, then pop top and push pop+5

   Push 10: stack top to bottom 10, 6, 4, 2. Pop removes 10, 10 + 5 = 15, push 15: top to bottom 15, 6, 4, 2.

3. Final Answer:

   15, 6, 4, 2 -> Option A

4. Quick Check:

   Stack after operations = 15, 6, 4, 2 [OK]

Hint: Track push/pop stepwise to find final stack [OK]

Common Mistakes:

• Confusing pop value used for new push
• Forgetting pop removes top element
• Assuming push adds without removing