C# | Index of first occurrence in StringCollection
Last Updated :
11 Jul, 2025
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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:
CSHARP
CSHARP
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"));
}
}
// 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:
Example 2:
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"));
}
}
// 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:
Reference:
-1