Create a Stack from a collection in C#

To create a Stack from a collection in C#, you can use the Stack<T> constructor that accepts an IEnumerable<T> parameter. This allows you to initialize a stack with elements from arrays, lists, or other collections.

Syntax

Following is the syntax for creating a Stack from a collection −

Stack<T> stack = new Stack<T>(IEnumerable<T> collection);

The elements are pushed in the reverse order of the collection enumeration.

Creating Stack from Array

The following example shows how to create a Stack from an existing array −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      int[] numbers = {100, 200, 300, 400, 500};
      
      Console.WriteLine("Original Array:");
      foreach(int val in numbers) {
         Console.WriteLine(val);
      }
      
      Stack<int> stack = new Stack<int>(numbers);
      
      Console.WriteLine("\nStack elements (LIFO order):");
      foreach(int val in stack) {
         Console.WriteLine(val);
      }
   }
}

The output of the above code is −

Original Array:
100
200
300
400
500

Stack elements (LIFO order):
500
400
300
200
100

Creating Stack from Another Stack

You can also create a Stack from another Stack using the ToArray() method −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Stack<string> originalStack = new Stack<string>();
      originalStack.Push("First");
      originalStack.Push("Second");
      originalStack.Push("Third");
      originalStack.Push("Fourth");
      
      Console.WriteLine("Original Stack:");
      foreach(string val in originalStack) {
         Console.WriteLine(val);
      }
      
      Stack<string> newStack = new Stack<string>(originalStack.ToArray());
      
      Console.WriteLine("\nNew Stack from ToArray():");
      foreach(string val in newStack) {
         Console.WriteLine(val);
      }
   }
}

The output of the above code is −

Original Stack:
Fourth
Third
Second
First

New Stack from ToArray():
First
Second
Third
Fourth

Creating Stack from List

Here's how to create a Stack from a List collection −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      List<int> numbers = new List<int> {10, 20, 30, 40, 50};
      
      Console.WriteLine("List elements:");
      foreach(int val in numbers) {
         Console.WriteLine(val);
      }
      
      Stack<int> stack = new Stack<int>(numbers);
      
      Console.WriteLine("\nStack from List:");
      foreach(int val in stack) {
         Console.WriteLine(val);
      }
      
      Console.WriteLine("\nPopping elements:");
      while(stack.Count > 0) {
         Console.WriteLine("Popped: " + stack.Pop());
      }
   }
}

The output of the above code is −

List elements:
10
20
30
40
50

Stack from List:
50
40
30
20
10

Popping elements:
Popped: 50
Popped: 40
Popped: 30
Popped: 20
Popped: 10

How It Works

When creating a Stack from a collection, the constructor iterates through the collection and pushes each element onto the stack. This results in the last element of the collection becoming the top of the stack (LIFO - Last In, First Out principle).

Conclusion

Creating a Stack from a collection in C# is straightforward using the Stack<T>(IEnumerable<T>) constructor. The key point to remember is that the collection elements are pushed in reverse order, making the last collection element the top of the stack, maintaining the LIFO behavior.