Sample code for substring with out using string functions in c#.

private static string CustomSubstring(int startIndex)

        {

            string input = "Hello! how r u?";

            return input.ToCharArray().Skip(startIndex).Aggregate("", (a, b) => a + b);

        }



        private static string CustomSubstring(int startIndex, int length)

        {

            string input = "Hello! how r u?";

            return input.ToCharArray().Skip(startIndex).Take(length).Aggregate("", (a, b) => a + b);           

        }

Best Regards,
Niladri Biswas

private static string CustomSubstring(int startIndex)

        {

            string input = "Hello! how r u?";

            int len = input.Length;

            string result = string.Empty;



            for (int i = 0; i < len; i++)

            {

                if(i >=startIndex)

                    result += input[i];

            }

            return result;

        }



        private static string CustomSubstring(int startIndex, int length)

        {

            string input = "Hello! how r u?";

            int len = input.Length;

            string result = string.Empty;



            for (int i = 0; i < len; i++)

            {

                if (i >= startIndex && i <= startIndex + length)

                    result += input[i];

            }

            return result;

        }

Best Regards,
Niladri Biswas