Calculate elapsed time

How to calculate elapsed time between two moments in C#:

using System;
using System.IO;
using System.Diagnostics;

    //Main function
    public void Main() {

      //Variables
      int i;
      int Iterations;
      double Seconds;
      Stopwatch StWatch;

      //Start time count
      StWatch = new Stopwatch();
      StWatch.Start();

      //Loop
      Iterations=1000000;
      for(i=0;i<Iterations;i++){
        ...
      }

      //Print statistics
      StWatch.Stop();
      Seconds=((double)StWatch.ElapsedMilliseconds/(double)1000);
      Console.WriteLine("Iterations:"+Iterations.ToString("#,##0")+", ElapsedSeconds: "+Seconds.ToString("0.00"));

    }