Can any one see what's the issue?

        static void Main(string[] args)
        {
            string input = Console.In.ReadToEnd();

            var valid = new char[] { '1', '2', '3', '4', '5', '6', '7', '8', '9', '0' };
            var sb = new StringBuilder();
            var numbers = new Stack<string>();
            for (int i = 0; i < input.Length; i++ )
            {
                if(valid.Contains(input[i]))
                {
                    sb.Append(input[i]);
                }
                else if(sb.Length > 0)
                {
                    numbers.Push(sb.ToString());
                    sb.Clear();
                }
            }

            NumberFormatInfo nfi = NumberFormatInfo.InvariantInfo;
            foreach(var n in numbers)
            {
                double sqrt = Math.Sqrt(double.Parse(n, nfi));
                Console.WriteLine(string.Format(nfi, "{0:F4}", sqrt));
            }

        }

.

Edited by author 16.01.2015 20:50

If the input stream ends with a digit, your code will lose it. For debugging - replace Console.In.ReadToEnd with Console.ReadLine and try to read string with one symbol "1"