C# Stack<T> Class

Stack<T> is a generic collection class which is used to maintain a last-in, first-out(LIFO) collection of same type of objects i.e. the last element to enter the Stack<T> is the first one to be removed. In other words, Stack<T> can be thought of as a pile of dishes, a new dish is always added to the top of the pile and the first dish to be removed is from the top as well.

Note: Stack<T>. It implements the ICollection, IEnumerable, and IEnumerable<T> interfaces.

Important features of Stack<T>

New elements are always added at the end of the Stack<T>.
Elements are removed from the end of the Stack<T>
Duplicate elements are allowed to be stored in a Queue.
As a Stack<T> maintains a LIFO collection of objects, so you may use Stack<T> when you need to access the information in reverse order.
To iterate over the elements of Stack<T>, we could use the foreach loop.

Constructors of Stack<T>

Constructor	Description
Stack<T>()	This constructor creates an empty instance of the Stack<T> class by using the default initial capacity. The capacity of a Stack<T> is the number of elements it can hold, as the new elements are added to the Stack<T>, its capacity is automatically increased.
Stack<T>(int capacity)	This constructor initializes created a Stack<T> that is empty and has the specified initial capacity..
Stack<T>(IEnumerable<T>)	This constructor creates a Stack<T> initialized with the elements of an IEnumerable<T>.

Properties of Stack<T>:

Properties	Description
Count	This property gives total number of elements in a Stack<T>.
IsSynchronzied	This property determines whether an ICollection is thread-safe or not.
SyncRoot	Thie property gets an object that can be used to synchronize access to the ICollection

Some commonly used methods of Stack<T> class

Methods	Description
T Pop()	This method removes and returns the object at the top of the Stack<T>.
T Push(T ob)	This method inserts an object at the top of the Stack<T>.
T Peek()	This method returns the object at the top of the Stack<T> without removing it.
bool Contains(T object)	This method checks if Stack<T> contains a specific object.
void Clear()	This method removes all of the elements from the Stack<T>.
Stack<T>.Enumerator GetEnumerator()	This method returns an IEnumerator to enumerate the entire Stack<T>.
T[ ] ToArray()	This method returns an array of type T, containing all the elements of a Stack<T>.

An example of Stack<T>

In this program we have created a Stack<T> to hold int values, and because C# has a unified type system, so any primitive values like int, char, float, etc are implicitly boxed into an Object reference.

Next, we will add and remove objects from it using methods. Let's see the code now -:

//C# Example of a Stack<T>


using System;
using System.Collections.Generic;

class StackEx
{
public static void Main(String[] ar)
{
	//Creating a Stack<T> of int type i.e Stack<int>, to hold int values
	Stack<int> st= new Stack<int>();
	

	//Calling the Push() method to push elements into the Stack<int>
	//New element is always added to the top of the Stack<int>
	st.Push(10);
	st.Push(32);
	st.Push(12);
	st.Push(3);
	st.Push(27);

	//Printing the contents of Stack<int>
	Console.WriteLine("The contents of Stack<int>: ");
	foreach(int element in st)
		Console.WriteLine(element);


	//Calling the Pop() method to remove the top element of the Stack<int>
	Console.WriteLine("Popping out the top element = "+ st.Pop());
	Console.WriteLine("Popping out the next top element = "+ st.Pop());


	//Calling the Peek() method which only gets the top element of the Stack<int>, without removing it
	Console.WriteLine("Peeking at the current top element = "+ st.Peek());


	//Printing the updated contents of Stack<int>
	Console.WriteLine("The updated contents of Stack<int>: ");
	foreach(int element in st)
		Console.WriteLine(element);
}
}

Output is :

The contents of Stack:
27
3
12
32
10
Popping out the top element = 27
Popping out the next top element = 3
Peeking at the current top element = 12
The pdated contents of Stack:
12
32
10

Program Analysis

The method Push() is called to add the elements to the top of Stack<T> and its contents are printed using foreach loop.
The method Pop() is called, which returns and removes the first/top element from the Stack<T> i.e. 27.
The method Pop() is called again, which returns and removes the next first/top element from the Stack<T> i.e. 3.
The method Peek() is called, which returns(but doesn't remove) the element from the top of Stack<T> i.e. 12. The updated contents of Stack<T> are displayed.

Converting a Stack<T> to an array of type T

In the upcoming program, we will call the ToArray(), which returns an Object array containing all the elements of the invoked Stack<T>.

//C# Example of calling the ToArray() method of Stack<T>

using System;
using System.Collections.Generic;

class StackEx
{
public static void Main(String[] ar)
{
	//Creating a Stack<T> of char type, i.e Stack<char>, to hold characters
	Stack<char> st= new Stack<char>();
	

	//Calling the Push() method to push elements into the Stack<T>
	//New element is always added to the top of the Stack<T>
	st.Push('e');
	st.Push('a');
	st.Push('x');
	st.Push('E');
	st.Push('B');

	//Printing the contents of Stack<char>
	Console.WriteLine("The contents of Stack<char>: ");
	foreach(char element in st)
		Console.WriteLine(element);

	//Calling the ToArray() method of Stack<char>
	char[] chArr = st.ToArray();


	//Printing the contents of Object array
	Console.WriteLine("The contents of char array initialized from the elements of Stack<char>: ");
	foreach(char element in chArr)
		Console.WriteLine(element);
}
}

Output is :

The contents of Stack<char>:
B
E
x
a
e
The contents of char array initialized from the elements of Stack<char>:
B
E
x
a
e

Program Analysis

The method Push() is called to add the elements to the top of Stack<char> and its contents are printed using foreach loop.
The method ToArray() is called, which returns a char array containing all the elements of the invoked Stack<char>.
The characters within the char array are iterated and displayed using the foreach method.

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