Just put >> output.txt when executing file.
After compile you have an "simple.exe" file. If you want to get output to a file you can just type in simple.exe >> output.txt (>> appends to file and > creates a new)
namespace Simple{class Program{static void Main(string[] args){for (int i = 0; i < args.Count(); i++){Console.WriteLine(string.Format("arg[{0}]: {1} ",i,args[i]));}}}}
Easy. You can also use the same method to write any output to file ie. when compiling from command line.