A stack follows the Last In, First Out (LIFO) or First In, Last Out (FILO) order, which means that the last element added to the stack is the first one to be removed.
To manage a stack, a pointer to the top is maintained, allowing access only to the top element.
Basic operations include push, pop, peek, isempty, top, and size.
Two types of stacks exist: dynamic (adjusting size dynamically) and static (fixed size).
Stacks can be implemented using arrays or linked lists.
Implementing Stack using Arrays
Implementing Stack a Linked List
Implement a stack using singly linked list
using System; // Create Stack Using Linked list public class StackUsingLinkedlist { // A linked list node private class Node { // integer data public int data; // reference variable Node type public Node link; } // create global top reference variable Node top; // Constructor public StackUsingLinkedlist() { this.top = null; } // Utility function to add // an element x in the stack // insert at the beginning public void push(int x) { // create new node temp and allocate memory Node temp = new Node(); // check if stack (heap) is full. // Then inserting an element // would lead to stack overflow if (temp == null) { Console.Write("\nHeap Overflow"); return; } // initialize data into temp data field temp.data = x; // put top reference into temp link temp.link = top; // update top reference top = temp; } // Utility function to check if // the stack is empty or not public bool isEmpty() { return top == null; } // Utility function to return // top element in a stack public int peek() { // check for empty stack if (!isEmpty()) { return top.data; } else { Console.WriteLine("Stack is empty"); return -1; } } // Utility function to pop top element from the stack public void pop() // remove at the beginning { // check for stack underflow if (top == null) { Console.Write("\nStack Underflow"); return; } // update the top pointer to // point to the next node top = (top).link; } public void display() { // check for stack underflow if (top == null) { Console.Write("\nStack Underflow"); return; } else { Node temp = top; while (temp != null) { // print node data Console.Write(temp.data); // assign temp link to temp temp = temp.link; if(temp != null) Console.Write(" -> "); } } } } // Driver code public class GFG { public static void Main(String[] args) { // create Object of Implementing class StackUsingLinkedlist obj = new StackUsingLinkedlist(); // insert Stack value obj.push(11); obj.push(22); obj.push(33); obj.push(44); // print Stack elements obj.display(); // print Top element of Stack Console.Write("\nTop element is {0}\n", obj.peek()); // Delete top element of Stack obj.pop(); obj.pop(); // print Stack elements obj.display(); // print Top element of Stack Console.Write("\nTop element is {0}\n", obj.peek()); } } 
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