oop

namespace ConsoleApp7
{
    internal class Program
    {
        static void Main(string[] args)
        {
            string path = "file.txt";
            string text = "root startsart faaaasast";
            string smax; //slovo
            string s = "";
            int kmax;    //chetchik
            int km;
            int k = 0;
            char[] g = { 'a','e','i','o','u','y'};

            // полная перезапись файла
            using (StreamWriter writer = new StreamWriter(path, false))
            {
                 writer.WriteLine(text);
            }

            using (StreamReader reader = new StreamReader(path))
            {
                char a = (char)reader.Read();
                while (reader.Peek() != -1)
                {
                    if ( ! g.Contains(a))
                    {
                        s = s+a;
                        k = k++;
                        km =
                    }
                    kmax = k;

                }

                Console.WriteLine(text);
            }
        }
    }
}