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Stack.Peek Method

Returns the object at the top of the Stack without removing it.

Namespace:  System.Collections
Assembly:  mscorlib (in mscorlib.dll)

public virtual Object Peek()

Return Value

Type: System.Object
The Object at the top of the Stack.

ExceptionCondition
InvalidOperationException

The Stack is empty.

This method is similar to the Pop method, but Peek does not modify the Stack.

null can be pushed onto the Stack as a placeholder, if needed. To distinguish between a null value and the end of the stack, check the Count property or catch the InvalidOperationException, which is thrown when the Stack is empty.

This method is an O(1) operation.

The following example shows how to add elements to the Stack, remove elements from the Stack, or view the element at the top of the Stack.

 using System;
 using System.Collections;
 public class SamplesStack  {

    public static void Main()  {

       // Creates and initializes a new Stack.
       Stack myStack = new Stack();
       myStack.Push( "The" );
       myStack.Push( "quick" );
       myStack.Push( "brown" );
       myStack.Push( "fox" );

       // Displays the Stack.
       Console.Write( "Stack values:" );
       PrintValues( myStack, '\t' );

       // Removes an element from the Stack.
       Console.WriteLine( "(Pop)\t\t{0}", myStack.Pop() );

       // Displays the Stack.
       Console.Write( "Stack values:" );
       PrintValues( myStack, '\t' );

       // Removes another element from the Stack.
       Console.WriteLine( "(Pop)\t\t{0}", myStack.Pop() );

       // Displays the Stack.
       Console.Write( "Stack values:" );
       PrintValues( myStack, '\t' );

       // Views the first element in the Stack but does not remove it.
       Console.WriteLine( "(Peek)\t\t{0}", myStack.Peek() );

       // Displays the Stack.
       Console.Write( "Stack values:" );
       PrintValues( myStack, '\t' );
    }


    public static void PrintValues( IEnumerable myCollection, char mySeparator )  {
       foreach ( Object obj in myCollection )
          Console.Write( "{0}{1}", mySeparator, obj );
       Console.WriteLine();
    }

 }


 /* 
 This code produces the following output.

 Stack values:    fox    brown    quick    The
 (Pop)        fox
 Stack values:    brown    quick    The
 (Pop)        brown
 Stack values:    quick    The
 (Peek)        quick
 Stack values:    quick    The
 */

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0
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