C#: Writing binary file

using System;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;

namespace FileIOText
{
class WriteBinaryFile
{
const String filename = "binfile.dat";
public WriteBinaryFile()
{
if(File.Exists(filename)){
Console.WriteLine("{0} already exists!", filename);
return;
}
FileStream fs = new FileStream(filename, FileMode.CreateNew);
/*
//create writer
BinaryWriter bw = new BinaryWriter(fs);

//create test data to write to file
int i = 299;
double d = 2.5999;
bool b = false;
String s = "Haha";
char c = 'A';

bw.Write(i);
bw.Write(d);
bw.Write(b);
bw.Write(s);
bw.Write(c);
*/

Dog d = new Dog("Rocky", 16);
Dog e = new Dog("Waggie", 10);
BinaryFormatter formatter = new BinaryFormatter();
formatter.Serialize(fs, d);
formatter.Serialize(fs, e);
//bw.Close();
fs.Close();
}
}
}