Stack.Peek Method in C#

This method(comes under System.Collections namespace) is used to return the object at the top of the Stack without removing it. This method is similar to the Pop method, but Peek does not modify the Stack.

Syntax:

public virtual object Peek ();

Return Value: It returns the Object at the top of the Stack.

Exception: Calling Peek() method on empty stack will throw InvalidOperationException. So always check for elements in the stack before retrieving elements using the Peek() method.

Below given are some examples to understand the implementation in a better way.

Example 1:

// C# code to illustrate the
// Stack.Peek Method
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a Stack
        Stack myStack = new Stack();

        // Inserting the elements into the Stack
        myStack.Push("1st Element");
        myStack.Push("2nd Element");
        myStack.Push("3rd Element");
        myStack.Push("4th Element");
        myStack.Push("5th Element");
        myStack.Push("6th Element");

        // Displaying the count of elements
        // contained in the Stack
        Console.Write("Total number of elements"+
                         " in the Stack are : ");

        Console.WriteLine(myStack.Count);

        // Displaying the top element of Stack
        // without removing it from the Stack
        Console.WriteLine("Element at the top is : "
                                  + myStack.Peek());

        // Displaying the top element of Stack
        // without removing it from the Stack
        Console.WriteLine("Element at the top is : "
                                + myStack.Peek());

        // Displaying the count of elements
        // contained in the Stack
        Console.Write("Total number of elements "+
                           "in the Stack are : ");

        Console.WriteLine(myStack.Count);
    }
}

Output:

Total number of elements in the Stack are : 6
Element at the top is : 6th Element
Element at the top is : 6th Element
Total number of elements in the Stack are : 6

Example 2:

// C# code to illustrate the
// Stack.Peek Method
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a Stack
        Stack myStack = new Stack();

        // Displaying the top element of Stack
        // without removing it from the Stack
        // Calling Peek() method on empty stack
        // will throw InvalidOperationException.
        Console.WriteLine("Element at the top is : "
                               + myStack.Peek());
    }
}

Runtime Error:

Unhandled Exception:
System.InvalidOperationException: Stack empty.

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.stack.peek?view=netframework-4.7.2