C# Stack Class (original) (raw)

Last Updated : 31 Jan, 2025

In C#, the Stack class represents a Last-in-First-out (LIFO) collection of objects. The stack is the part of the **System.Collections.Generic namespace. This class allows us to push elements onto the stack, pop elements from the stack, and peek at the top element without removing it.

• The capacity of a Stack is the number of elements the Stack can hold. As elements are added to a Stack, the capacity is automatically increased as required through reallocation.
• If the Count is less than the capacity of the stack, Push is an _O(1) operation. If the capacity needs to be increased to accommodate the new element, Push becomes an O(n) operation, where _n is Count. Pop is an O(1) operation.
• Stack accepts null as a valid value and allows duplicate elements.

**Example: This example demonstrates how to use Stack to push and pop elements in LIFO order.

C# `

// C# program Implementing Stack class using System; using System.Collections.Generic;

public class Geeks { public static void Main(string[] args) { // Create a new stack Stack s = new Stack();

    // Push elements onto the stack
    s.Push(1);
    s.Push(2);
    s.Push(3);
    s.Push(4);

    // Pop elements from the stack
    while (s.Count > 0) {
        Console.WriteLine(s.Pop());
    }
}

}

`

Declaration of Stack

In C#, a Stack is declared using the Stackclass, where T is the type of element the stack will hold.

Stack stackName = new Stack();

Constructors

The Stack class provides three constructor which are listed below in the table:

**Example: This example demonstrates the basic operations of Stack such as adding an element, checking the Stack size and viewing the top element without modify the stack.

C# `

// C# program to perform // different operations in stack using System; using System.Collections;

class Geeks { public static void Main() { // Creating a Stack Stack s = new Stack();

    // Pushing elements into the Stack
    s.Push(10);
    s.Push(20);
    s.Push(30);
    s.Push(40);
    s.Push(50);
    s.Push(60);

    // Displaying the count of elements in the Stack
    Console.Write("Total elements in Stack: ");
    Console.WriteLine(s.Count);

    // Displaying the top element of the Stack without
    // removing it
    Console.WriteLine("Top element is: " + s.Peek());

    // Displaying the top element of the Stack again
    Console.WriteLine("Top element again is: "
                      + s.Peek());

    // Displaying the updated count of elements
    Console.Write("Updated count of elements: ");
    Console.WriteLine(s.Count);
}

}

`

Output

Total elements in Stack: 6 Top element is: 60 Top element again is: 60 Updated count of elements: 6

Properties

The Stack class provides several properties to access its state.

**Example: This example demonstrates the total number of elements in the Stack.

C# `

// C# program to get the number of // elements contained in the stack using System; using System.Collections;

class Geeks { public static void Main() { // Creating a Stack Stack s = new Stack();

    // Inserting the elements into the Stack
    s.Push(10);
    s.Push(20);
    s.Push(30);
    s.Push(40);
    s.Push(50);
    s.Push(60);

    // Displaying the count of elements in the Stack
    Console.Write(
        "Total number of elements in the Stack are: ");
    Console.WriteLine(s.Count);
}

}

`

Output

Total number of elements in the Stack are: 6

Methods

**Example: This example demonstrates how to use clear() to clear all the elements from the stack.

C# `

// C# code to Remove all // objects from the Stack using System; using System.Collections;

class Geeks { public static void Main() { // Creating a Stack Stack s = new Stack();

    // Inserting elements into the Stack
    s.Push(10);
    s.Push(20);
    s.Push(30);
    s.Push(40);
    s.Push(50);
    s.Push(60);

    // Displaying the count of elements
    //  before clearing the Stack
    Console.Write(
        "Total elements in Stack before clear: ");
    Console.WriteLine(s.Count);

    // Removing all elements from the Stack
    s.Clear();

    // Displaying the count of elements 
    // after clearing the Stack
    Console.Write(
        "Total elements in Stack after clear: ");
    Console.WriteLine(s.Count);
}

}

`

Output

Total elements in Stack before clear: 6 Total elements in Stack after clear: 0

**Example: This example demonstrates how to check if a specific element is present in a stack using the Contains().

C# `

// C# Program to Check if a Stack // contains an element using System; using System.Collections;

class Geeks { public static void Main() {

    // Creating a Stack of strings
    Stack s = new Stack();

    // Inserting the elements into the Stack
    s.Push("Geek1");
    s.Push("Geek2");
    s.Push("Geek3");
    s.Push("Geek4");
    s.Push("Geek5");

    // Checking whether the element is
    // present in the Stack or not
    Console.WriteLine("The element Geek2 is present? :"
                      + s.Contains("Geek2"));
    Console.WriteLine("The element Geek10 is present? :"
                      + s.Contains("Geek10"));
}

}

`

Output

The element Geek2 is present? :True The element Geek10 is present? :False