C# | Index of first occurrence in StringCollection - GeeksforGeeks

01 Feb, 2019
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 StringCollectionusing 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"));    }}
2

Example 2:
// C# code to search string and returns// the zero-based index of the first// occurrence in StringCollectionusing 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"));    }}
-1

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