C# Stack with Examples

In C# a Stack is a Collection that follows the Last-In-First-Out (LIFO) principle. It is used when we need last-in, first-out access to items. In C# there are both generic and non-generic types of Stacks. The generic stack is in the System.Collections.Generic namespace, while the non-generic stack is in System.Collections. The stack can dynamically store elements of the same or different types.

Example: This example demonstrates the basic working of Stack.

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Below is the diagramatic Representation of Working of Stack:

Hierarchy of Stack Class

The below diagram shows the Hierarchy of Stack class.

• The Stack class implements the IEnumerable, ICollection, and ICloneable interfaces.
• When we add an item to the list, it is called pushing the element.
• When we remove it, it is called popping the element.
• 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.
• In Stack, we are allowed to store duplicate elements.
• A Stack accepts null as a valid value for reference types.

Creating a Stack

Stack class has three constructors which are used to create a stack which is as follows:

• Stack(): This constructor is used to create an instance of the Stack class which is empty and having the default initial capacity.
• Stack(ICollection): This constructor is used to create an instance of the Stack class which contains elements copied from the specified collection, and has the same initial capacity as the number of elements copied.
• Stack(Int32): This constructor is used to create an instance of the Stack class which is empty and having specified initial capacity or the default initial capacity, whichever is greater

Let’s see how to create a stack using Stack() constructor:

Step 1: Include System.Collections namespace in your program with the help of using keyword

using System.Collections;

Step 2: Create a Stack using Stack class

Stack s = new Stack();

Performing Various Operations on Stack

1. Adding Elements: We use push() method to insert elements in a stack.

Example: This example demonstrates how to create non-generic stack, add various elements to it and access them in Last-In-FIrst-Out (LIFO) Order.

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2. Removing Elements:The Stack class provides two different methods to remove elements and the methods are listed below:

• Clear() Method: The clear() is used to remove all the objects from the stack.
• Pop Method(): The pop() is used to removes the beginning element of the stack.

Example: This example displays the contents of the stack before and after removal.

Initial stack: 
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Updated stack after Pop:
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3. Get the Topmost Element of the Stack: The Stack class provides two different methods to find the topmost element of the stack and the methods are listed below:

• Pop() Method: The Pop()method returns the object at the beginning of the stack with modification means this method removes the topmost element of the stack.
• Peek() Method: The Peek()method returns the object at the beginning of the stack without removing it.

Example: This example demonstrates how to peek at the topmost element of a Stack.

The topmost element in the stack is: 30

4. Checking the Availability of Elements in the Stack: Stack class provide Contains() method to check if the element is present in the Stack or not.

Example:

The element 20 is present in the stack: True
The element 100 is present in the stack: False

Generic Stack vs Non-Generic Stack