best for to generate id for user

 private static int getID()
 {
	    //read new id from file and return it 
            // 100 is Base id
            int id;
            if (File.Exists("id.txt"))
            {
                TextReader tr = new StreamReader("id.txt");
                id = Int32.Parse(tr.ReadLine());
                id++;
                tr.Close();
                File.WriteAllText(@"id.txt", string.Empty);
                TextWriter tw = new StreamWriter("id.txt");
                tw.WriteLine(id);
                tw.Close();
            }
            else
            {
                id = 100;
                TextWriter tw = new StreamWriter("id.txt");
                tw.WriteLine(id);
                tw.Close();
            }
            return id;
}