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C# | Index of first occurrence in StringCollection

C# | Index of first occurrence in StringCollection

Last Updated : 11 Jul, 2025

StringCollection class is a new addition to the .NET Framework class library that represents a collection of strings. StringCollection class is defined in the

System.Collections.Specialized

namespace.

StringCollection.IndexOf(String)

method is used to search the specified string which returns the zero-based index of the first occurrence within the StringCollection.

Syntax: 
public int IndexOf (string value);

Here,

value

is the string to locate. The value can be null.

Return Value:

The method returns zero-based index of the first occurrence of

value

in the StringCollection, if found otherwise it returns -1.

Note:

This method performs a

linear search

. Therefore, this method is an O(n) operation, where n is Count. Below programs illustrate the use of

StringCollection.IndexOf(String)

method:

Example 1: CSHARP 
// C# code to search string and returns
// the zero-based index of the first
// occurrence in StringCollection
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // creating a StringCollection named myCol
        StringCollection myCol = new StringCollection();

        // creating a string array named myArr
        String[] myArr = new String[] { "A", "B", "C", "C", "D" };

        // Copying the elements of a string
        // array to the end of the StringCollection.
        myCol.AddRange(myArr);

        // To search string "C" and return
        // the zero-based index of the first
        // occurrence in StringCollection
        // Here, "C" exists at index 2 and 3.
        // But, the method should return 2
        Console.WriteLine(myCol.IndexOf("C"));
    }
}
Example 2: CSHARP 
// C# code to search string and returns
// the zero-based index of the first
// occurrence in StringCollection
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // creating a StringCollection named myCol
        StringCollection myCol = new StringCollection();

        // creating a string array named myArr
        String[] myArr = new String[] { "2", "3", "4", "5", "6" };

        // Copying the elements of a string
        // array to the end of the StringCollection.
        myCol.AddRange(myArr);

        // To search string "9" and return
        // the zero-based index of the first
        // occurrence in StringCollection
        // Here, "9" does not exist in myCol
        // Hence, method returns -1
        Console.WriteLine(myCol.IndexOf("9"));
    }
}
Reference:

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