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Some versions of the LastIndexOf() method




Methods	Description
LastIndexOf(char ch)	It returns the last index of a char ch found in the String object.
LastIndexOf(char ch, int index)	It returns the last index of a char value(if found) in the String object. The search starts at a specified index position and proceeds backwards toward the beginning of the invoked String.
LastIndexOf(String str)	It returns the last index of a String str found in the String object.
LastIndexOf(String str, int index)	It returns the last index of a String value(if found) in the String object. The search starts at a specified index position and proceeds backwards toward the beginning of the invoked String.
LastIndexOf(String str, StringComparison)	It returns the last index of a String value(if found) in the String object. The search is performed on the basis of the specified field of type StringComparison.








Note :


LastIndexOf() method returns -1 if the searched char/string(passed to this method) is not found in the invoked String object.






Example of LastIndexOf(char) method


In the upcoming example, we are going to search for the last index of a particular char value in the invoked String object by using the LastIndexOf() method. If the searched char is found, its last index is returned, otherwise if the char is not found then -1 is returned.



// C# Example of LastIndexOf(char)

using System;

class StringIndex1
{
public static void Main()
{
	//Creating a String object
	String str1 = "Let us decode CSharp!";
	
	//Priting the String object		
	Console.WriteLine("String: " + str1);

	//Calling the LastIndexOf() method 
	int index = str1.LastIndexOf('e');
	Console.WriteLine("Last Index of 'e' in " + str1 +  " : "+ index);

	//Calling the LastIndexOf() method 
	index = str1.LastIndexOf('d');
	Console.WriteLine("Last Index of 'd' in " + str1 +  " : "+ index);

	//Calling the LastIndexOf() method 
	index = str1.LastIndexOf('z');
	Console.WriteLine("Last Index of 'z' in " + str1 +  " : "+ index);

	//Calling the LastIndexOf() method 
	index = str1.LastIndexOf('x');
	Console.WriteLine("Last Index of 'x' in " + str1 +  " : "+ index);
	
	//Calling the LastIndexOf() method 
	index = str1.LastIndexOf('!');
	Console.WriteLine("Last Index of '!' in " + str1 +  " : "+ index);	
}
}





Output is :




String: Let us decode CSharp!
Last Index of 'e' in Let us decode CSharp! : 12
Last Index of 'd' in Let us decode CSharp! : 11
Last Index of 'z' in Let us decode CSharp! : -1
Last Index of 'x' in Let us decode CSharp! : -1
Last Index of '!' in Let us decode CSharp! : 20





Program Analysis



String is initialized with value Let us decode CSharp!
• The Last occurrence of char value e in the String object is found at index 12.
• The Last occurrence of char value d in the String object is found at index 11.
• The last occurrence of char value z in the String is not found, hence -1 is returned.
• The Last occurrence of char value x in the String is not found, therefore, -1 is returned.
• The Last occurrence of char value ! in the String object is at index 20.







Example of LastIndexOf(char char, int startIndex) method


In the upcoming example, we are going to discuss a different overloaded version of lastIndexOf method i.e. LastIndexOf(char, int), which returns the last index of a char value(if found) in the String object. The search starts at a specified index position and proceeds backwards toward the beginning of the invoked String.



//C# Example of LastIndexOf(char, int)


using System;

class StringIndex1
{
public static void Main()
{
	//Creating a String object 
	String str = "Blue Sky Blue";

	//Printing the String object
	Console.WriteLine("String: "+ str);

	//Calling the LastIndexOf() method
	int index = str.LastIndexOf('u', 6);
	Console.WriteLine("Last Index of 'u' starting at index 6 in " + str +  " : "+ index);

	//Calling the LastIndexOf() method	
	index = str.LastIndexOf('u', 12);
	Console.WriteLine("Last Index of 'u' starting at index 12 in " + str +  " : "+ index);
	

	//Calling the LastIndexOf() method	
	index = str.LastIndexOf('B', 4);
	Console.WriteLine("Last Index of 'B' starting at index 4 in " + str +  " : "+ index);


	//Calling the LastIndexOf() method	
	index = str.LastIndexOf('B', 10);
	Console.WriteLine("Last Index of 'B' starting at index 10 in " + str +  " : "+ index);


	//Calling the LastIndexOf() method	
	index = str.LastIndexOf('S', 3);
	Console.WriteLine("Last Index of 'S' starting at index 3 in " + str +  " : "+ index);
}
}





Output is :




String: Blue Sky Blue
Last Index of 'u' starting at index 6 in Blue Sky Blue : 2
Last Index of 'u' starting at index 12 in Blue Sky Blue : 11
Last Index of 'B' starting at index 4 in Blue Sky Blue : 0
Last Index of 'B' starting at index 10 in Blue Sky Blue : 9
Last Index of 'S' starting at index 3 in Blue Sky Blue : -1








Example of LastIndexOf(String) method.


In this next example, we are going to discuss another version of LastIndexOf method i.e. LastIndexOf(String), which searches for the last index of a particular String value in the invoked String object.



//C# Example of LastIndexOf(String)


using System;

class StringIndex1
{
public static void Main()
{
	//Creating a String object 
	String str = "Blue Sky Blue";


	//Printing the String object
	Console.WriteLine("String: "+ str);


	//Calling the LastIndexOf() method
	int index = str.LastIndexOf("Blue");
	Console.WriteLine("Last Index of Blue in " + str +  " : "+ index);


	//Calling the LastIndexOf() method	
	index = str.LastIndexOf("Sky");
	Console.WriteLine("Last Index of Sky in " + str +  " : "+ index);
	

	//Calling the LastIndexOf() method	
	index = str.LastIndexOf("Ting");
	Console.WriteLine("Last Index of Ting in " + str +  " : "+ index);
}
}





Output is :




String: Blue Sky Blue
Last Index of Blue in Blue Sky Blue : 9
Last Index of Sky in Blue Sky Blue : 5
Last Index of Ting in Blue Sky Blue : -1





Program Analysis



String is initialized with value Blue Sky Blue
• The last occurrence of the String Blue in the String object is found at the index 9.
• The last occurrence of the String Sky in the String object is found at the index 5.
• The last occurrence of the String Hi in the String object is not found, hence -1 is returned.





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Example of LastIndexOf(String str, int startIndex) method


In the upcoming example, we are going to discuss a different overloaded version of lastIndexOf method i.e. LastIndexOf(String, int), which returns the last index of a String value(if found) in the String object. The search starts at a specified index position and proceeds backwards toward the beginning of the invoked String.



//C# Example of LastIndexOf(String, int)


using System;

class StringIndex1
{
public static void Main()
{
	//Creating a String object 
	String str = "Live and let live!";

	//Printing the String object
	Console.WriteLine("String: "+ str);

	//Calling the LastIndexOf() method
	int index = str.LastIndexOf("Live", 6);
	Console.WriteLine("Last Index of 'Live' starting at index 6 in " + str +  " : "+ index);

	//Calling the LastIndexOf() method	
	index = str.LastIndexOf("live", 6);
	Console.WriteLine("Last Index of 'live' starting at index 6 in " + str +  " : "+ index);
	

	//Calling the LastIndexOf() method	
	index = str.LastIndexOf("live", 16);
	Console.WriteLine("Last Index of 'live' starting at index 16 in " + str +  " : "+ index);


	//Calling the LastIndexOf() method	
	index = str.LastIndexOf("and", 10);
	Console.WriteLine("Last Index of 'and' starting at index 10 in " + str +  " : "+ index);


	//Calling the LastIndexOf() method	
	index = str.LastIndexOf("t", 12);
	Console.WriteLine("Last Index of 't' starting at index 12 in " + str +  " : "+ index);
}
}





Output is :




String: Live and let live!
Last Index of 'Live' starting at index 6 in Live and let live! : 0
Last Index of 'live' starting at index 6 in Live and let live! : -1
Last Index of 'live' starting at index 16 in Live and let live! : 13
Last Index of 'and' starting at index 10 in Live and let live! : 5
Last Index of 't' starting at index 12 in Live and let live! : 11



You must remember that the LastIndexOf() method performs a case-sensitive search and therefore, the LastIndexOf() method has returned -1 when searching for the String live(with a lowercase 'l'), starting from the index 6 proceeding backwards to the beginning of the invoked String.






Example of LastIndexOf(String, StringComparison)


In the upcoming code, we are going to explain another overload of LastIndexOf method i.e. LastIndexOf(String, StringComparison), which determines the last index of a String value(if found) in the String object. The search is performed on the basis of the specified field of type StringComparison Enum.

The StringComparison is an Enum which specifies culture, sort, case rules to be used by whem the comparison is made between String objects. Its all important 6 fields are explained below.




Fields of StringComparison	Value	Description
CurrentCulture	0	Compares String objects using culture-sensitive sort rules and current culture.
CurrentCultureIgnoreCase	1	Compares String objects using culture-sensitive sort rules and current culture, while ignoring the case of the String objects being compared.
InvariantCulture	2	Compares String objects using culture-sensitive sort rules and invariant culture.
InvariantCultureIgnoreCase	3	Compares String objects using culture-sensitive sort rules and invariant culture, while ignoring the case of the String objects being compared.
Ordinal	4	Compares String objects using ordinal(binary) sort rules.
OrdinalIgnoreCase	5	Compares String objects using ordinal(binary) sort rules, while ignoring the case of the String objects being compared.



Note: The LastIndexOf(String, StringComparison) method performs a case-sensitive search, unless you pass a specific field of StringComparison with IgnoreCase specified in it.



//C# Example of LastIndexOf(String, StringComparison) method of String.

using System;

class StringEx
{
public static void Main()
{
	String str1= "Live and let live!";
	Console.WriteLine("String is: "  + str1);


	//String comparison made using StringComparison.CurrentCulture
	Console.WriteLine("String comparison by StringComparison.CurrentCulture:");
	
	int index = str1.LastIndexOf("ive", StringComparison.CurrentCulture);
	Console.WriteLine("The last index of 'ive' in "+ str1 + " is at ? "+ index); 

	index = str1.LastIndexOf("Live", StringComparison.CurrentCulture);
	Console.WriteLine("The last index of 'Live' in "+ str1 + " is at ? "+ index);  



	//String comparison made using StringComparison.CurrentCultureIgnoreCase
	Console.WriteLine("String comparison by StringComparison.CurrentCultureIgnoreCase:");

	index = str1.LastIndexOf("LIVE", StringComparison.CurrentCultureIgnoreCase);
	Console.WriteLine("The last index of 'LIVE' in "+ str1 + " is at ? "+ index);

	index = str1.LastIndexOf("LET", StringComparison.CurrentCultureIgnoreCase);
	Console.WriteLine("The last index of 'LET' in "+ str1 + " is at ? "+ index); 

	

	//String comparison made using StringComparison.InvariantCulture
	Console.WriteLine("String comparison by StringComparison.InvariantCulture: ");

	index = str1.LastIndexOf("ive", StringComparison.InvariantCulture);
	Console.WriteLine("The last index of 'ive' in "+ str1 + " is at ? "+ index);  

	index = str1.LastIndexOf("Live", StringComparison.InvariantCulture);
	Console.WriteLine("The last index of 'Live' in "+ str1 + " is at ? "+ index); 



	//String comparison made using StringComparison.InvariantCultureIgnoreCase
	Console.WriteLine("String comparison by StringComparison.InvariantCultureIgnoreCase: ");

	index = str1.LastIndexOf("LIVE", StringComparison.InvariantCultureIgnoreCase);
	Console.WriteLine("The last index of 'LIVE' in "+ str1 + " is at ? "+ index);

	index = str1.LastIndexOf("LET", StringComparison.CurrentCultureIgnoreCase);
	Console.WriteLine("The last index of 'LET' in "+ str1 + " is at ? "+ index); 



	//String comparison made using StringComparison.Ordinal
	Console.WriteLine("String comparison by StringComparison.Ordinal: ");

	index = str1.LastIndexOf("ive", StringComparison.Ordinal);
	Console.WriteLine("The last index of 'ive' in "+ str1 + " is at ? "+ index);   

	index = str1.LastIndexOf("Live", StringComparison.Ordinal);
	Console.WriteLine("The last index of 'Live' in "+ str1 + " is at ? "+ index); 


	
	//String comparison made using StringComparison.OrdinalIgnoreCase
	Console.WriteLine("String comparison by StringComparison.OrdinalIgnoreCase: ");

	index = str1.LastIndexOf("LIVE", StringComparison.OrdinalIgnoreCase);
	Console.WriteLine("The last index of 'LIVE' in "+ str1 + " is at ? "+ index);

	index = str1.LastIndexOf("LET", StringComparison.CurrentCultureIgnoreCase);
	Console.WriteLine("The last index of 'LET' in "+ str1 + " is at ? "+ index); 
}
}





Output is :




String is: Live and let live!
String comparison by StringComparison.CurrentCulture:
The last index of 'ive' in Live and let live! is at ? 14
The last index of 'Live' in Live and let live! is at ? 0
String comparison by StringComparison.CurrentCultureIgnoreCase:
The last index of 'LIVE' in Live and let live! is at ? 13
The last index of 'LET' in Live and let live! is at ? 9
String comparison by StringComparison.InvariantCulture:
The last index of 'ive' in Live and let live! is at ? 14
The last index of 'Live' in Live and let live! is at ? 0
String comparison by StringComparison.InvariantCultureIgnoreCase:
The last index of 'LIVE' in Live and let live! is at ? 13
The last index of 'LET' in Live and let live! is at ? 9
String comparison by StringComparison.Ordinal:
The last index of 'ive' in Live and let live! is at ? 14
The last index of 'Live' in Live and let live! is at ? 0
String comparison by StringComparison.OrdinalIgnoreCase:
The last index of 'LIVE' in Live and let live! is at ? 13
The last index of 'LET' in Live and let live! is at ? 9







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