Get last index position of character

The function is used to find the last index position of the character in the given string

Create FUNCTION [dbo].[CharLastIndex](@SeekChars nvarchar(max),@String nvarchar(max))
RETURNS int
AS 
BEGIN   
    Declare @Index int,@startPosition int
    SET  @startPosition=0
    Select @Index= charindex(@SeekChars,@String,@startPosition)
    SET @startPosition = @Index
    While(@startPosition!=0)
    BEGIN
        SET @Index =@startPosition
        Select @startPosition = charIndex(@SeekChars,@String,@startPosition+1)
    END

RETURN @Index
END