Writing Text to files( C#.net )

private void button1_Click(object sender, EventArgs e)
{
 try
 {
  FileStream fileStrm = File.Open("c:\\testfile.txt", FileMode.OpenOrCreate);
  StreamWriter writer = new StreamWriter(fileStrm);
  writer.WriteLine("First Line");
  for (int i = 2; i < 100; i++)
  {
   writer.WriteLine("This is line {0}", i);