How to use C#'s BinaryWriter class?

static void WriteMe() {
   using (BinaryWriter w = new BinaryWriter(File.Open("C:\abc.txt", FileMode.Create))) {
      w.Write(37.8);
      w.Write("test”);
   }
}

static void ReadMe() {
   using (BinaryReader r = new BinaryReader(File.Open("C:\abc.txt", FileMode.Open))) {
      Console.WriteLine("Value : " + r.ReadDouble());
      Console.WriteLine("Value : " + r.ReadString());
   }
}

static void WriteMe() {
   using (BinaryWriter w = new BinaryWriter(File.Open("C:\abc.txt", FileMode.Create))) {

      w.Write(37.8);
      w.Write("test");
   }
}