C# | Index of first occurrence in StringCollection

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:

// 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"));
    }
}

Output:

2

Example 2:

// 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"));
    }
}

Output:

-1

Reference:

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