C# String LastIndexOf()

using System;  
namespace CsharpString {  
  class Test {
    public static void Main(string [] args) {
     
      string str = "Icecream";

      // returns last index of 'c'
      int index = str.LastIndexOf('c');

      Console.WriteLine(index);

      Console.ReadLine();    
    }
  }
}

// Output: 3

LastIndexOf() Syntax

The syntax of the string LastIndexOf() method is:

LastIndexOf(String value, int startIndex, int count, StringComparison comparisonType)

Here, LastIndexOf() is a method of class String.

LastIndexOf() Parameters

The LastIndexOf() method takes the following parameters:

• value - substring to seek
• startIndex - starting position of the search. The search proceeds from startIndex toward the beginning of the given string.
• count - number of character positions to examine.
• comparisonType - enumeration values that specifies the rules for the search

LastIndexOf() Return Value

• returns the index of the last occurrence of the specified character/string
• returns -1 if the specified character/string is not found.

Example 1: C# String LastIndexOf() With startIndex

using System;  
namespace CsharpString {  
  class Test {
    public static void Main(string [] args) {
     
      string str = "Icecream";

      // returns last index of 'c' 
      int index = str.LastIndexOf('c', 2);

      Console.WriteLine(index);

      Console.ReadLine();    
    }
  } 
}

Output

1

Notice the line,

int index = str.LastIndexOf('c', 2);

Here,

• c - char to seek
• 2 - starting index of search (search starts from index 2 towards the beginning of str)

Example 2: C# String LastIndexOf() With startIndex and count

using System;  
namespace CsharpString {  
  class Test {
    public static void Main(string [] args) {
     
      string str = "Icecream";

      int startIndex = 5;
      int count = 2;

      // returns -1  as 'c' is not found
      int index = str.LastIndexOf('c', startIndex, count);

      Console.WriteLine(index);

      Console.ReadLine();    
    }
  } 
}

Output

-1

Here,

int index = str.LastIndexOf('c', startIndex, count);

searches 2 characters ('e' and 'r') from index 5 towards the beginning of the str string.

Example 3: C# String LastIndexOf() With StringComparison

using System;  
namespace CsharpString {  
  class Test {
    public static void Main(string [] args) {
     
      string str = "icecream";

      int startIndex = 2;
      int count = 3;

      StringComparison comparisonType1 = StringComparison.CurrentCultureIgnoreCase;
      StringComparison comparisonType2 = StringComparison.CurrentCulture;

      // ignores letter case
      int index1 = str.LastIndexOf("CE", startIndex, count, comparisonType1);
      Console.WriteLine(index1);

       // considers letter case
      int index2 = str.LastIndexOf("CE", startIndex, count, comparisonType2);
      Console.WriteLine(index2);

      Console.ReadLine();    
    }
  }
}

Output

1
-1

Here,

• comparisonType1 - ignores letter case
• comparisonType2 - considers letter case