TextManip

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

namespace ConsoleApplication8
{
    class Program
    {
        static void Main(string[] args)
        {
            string Filename = "text.txt";
            int lastStr = 0;
            try
            {
                if (File.Exists(Filename))
                {
                    StreamReader sr = new StreamReader(Filename);
                    string line;
                    int lastLine = 0;
                    // string resultStr = "";
                    while ((line = sr.ReadLine()) != null)
                    {
                        if (line == "")
                            continue;
                        line = line.Replace(" ", "");
                        if (Char.IsDigit(line[0]))
                        {

                            if (line[1] == '.')
                        lastLine = line[0] - '0';
                            else if (Char.IsDigit(line[1]))
                            {
                                if (line[2] == '.')
                                {
                                    lastLine = Convert.ToInt16(string.Concat(line[0],line[1]));
                                }
                            }

                        }

                    }
                    lastStr = lastLine;
                    sr.Close();
                }
            }
            catch (Exception e)
            {
                Console.WriteLine("Exception type is {0} \n", e.GetType());
            }

            try
            {
                StreamWriter sw = new StreamWriter(Filename, true);
                int j = 1;
                for (int i = lastStr + 1; i < lastStr + 1+10; i++, j++)
                {
                    sw.WriteLine(i.ToString() + ". " + "Some text " + j);
                }

                sw.Close();
            }
            catch (Exception e)
            {
                Console.WriteLine("Exception type is {0} /n", e.GetType());
            }
        }
    }
}