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StringCollection.IndexOf Method

Searches for the specified string and returns the zero-based index of the first occurrence within the StringCollection.

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

public int IndexOf(
	string value


Type: System.String

The string to locate. The value can be null.

Return Value

Type: System.Int32
The zero-based index of the first occurrence of value in the StringCollection, if found; otherwise, -1.

This method determines equality by calling Object.Equals. String comparisons are case-sensitive.

This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.

Starting with the .NET Framework 2.0, this method uses the collection’s objects’ Equals and CompareTo methods on item to determine whether item exists. In the earlier versions of the .NET Framework, this determination was made by using the Equals and CompareTo methods of the item parameter on the objects in the collection.

The following code example searches the StringCollection for an element.

using System;
using System.Collections;
using System.Collections.Specialized;

public class SamplesStringCollection  {

   public static void Main()  {

      // Creates and initializes a new StringCollection.
      StringCollection myCol = new StringCollection();
      String[] myArr = new String[] { "RED", "orange", "yellow", "RED", "green", "blue", "RED", "indigo", "violet", "RED" };
      myCol.AddRange( myArr );

      Console.WriteLine( "Initial contents of the StringCollection:" );
      PrintValues( myCol );

      // Checks whether the collection contains "orange" and, if so, displays its index.
      if ( myCol.Contains( "orange" ) )
         Console.WriteLine( "The collection contains \"orange\" at index {0}.", myCol.IndexOf( "orange" ) );
         Console.WriteLine( "The collection does not contain \"orange\"." );


   public static void PrintValues( IEnumerable myCol )  {
      foreach ( Object obj in myCol )
         Console.WriteLine( "   {0}", obj );


This code produces the following output.

Initial contents of the StringCollection:

The collection contains "orange" at index 1.


Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0