String Reverse without predefined function in C#

class Program

    {

        static void Main(string[] args)

        {

            Console.WriteLine("Enter any String: ");

            string input = Console.ReadLine();

            string str = "";

            for (int i = input.Length - 1; i >= 0; i--)

            {

                if (input[i] == ' ')

                {

                    for (int j = str.Length - 1; j >= 0; j--)

                    {

                        Console.Write(str[j]);

                    }

                    if (i != 0)

                    {

                        Console.Write(" ");

                        str = "";

                    }

                }

                else

                {

                    str += input[i];

                    if (i == 0)

                        for (int j = str.Length - 1; j >= 0; j--)

                        {

                            Console.Write(str[j]);

                        }

                }

                }

            Console.ReadLine();

        }

    }

 
Output: