c# append to file

 using (FileStream fs = new FileStream(fileName,FileMode.Append, FileAccess.Write))
 using (StreamWriter sw = new StreamWriter(fs))
 {
    sw.WriteLine(something);
 }

File.AppendAllText(@"c:\path\file.txt", "text content" + Environment.NewLine);

using(StreamWriter writer = new StreamWriter("C:\\log.txt", true)) 
{ 
	writer.WriteLine("Line"); 
}