try/catch/finally, throw new बनाम rethrow

using System;

public class Program
{
  public static void Main(string[] args)
  {
    Console.WriteLine("Start");
    try
    {
      int x = 10;
      int y = 0; // will cause DivideByZeroException
      Console.WriteLine(x / y);
    }
    catch (DivideByZeroException ex)
    {
      Console.WriteLine("Cannot divide by zero: " + ex.GetType().Name);
    }
    Console.WriteLine("Continue");
  }
}

using System;

public class Program
{
  static int ParseAndDivide(string text, int divisor)
  {
    // Throws FormatException or DivideByZeroException
    int value = int.Parse(text);
    return value / divisor;
  }

  public static void Main(string[] args)
  {
    try
    {
      Console.WriteLine(ParseAndDivide("not-a-number", 2));
    }
    catch (FormatException)
    {
      Console.WriteLine("Bad number format");
    }
    catch (Exception ex)
    {
      // Fallback last
      Console.WriteLine("Other error: " + ex.GetType().Name);
    }
  }
}

using System;

public class Program
{
  static bool opened = false;

  static void UseFakeResource()
  {
    try
    {
      opened = true;
      Console.WriteLine("Open");
      throw new InvalidOperationException("boom");
    }
    catch (InvalidOperationException)
    {
      Console.WriteLine("Handled");
    }
    finally
    {
      opened = false; // cleanup path
      Console.WriteLine("Close");
    }
  }

  public static void Main(string[] args)
  {
    UseFakeResource();
    Console.WriteLine("Opened? " + opened);
  }
}

using System;

public class Program
{
  static void BadRethrow()
  {
    try
    {
      Fail();
    }
    catch (Exception ex)
    {
      // Resets stack trace:
      throw ex; // BAD rethrow
    }
  }

  static void GoodRethrow()
  {
    try
    {
      Fail();
    }
    catch
    {
      // Preserves original stack trace:
      throw; // GOOD rethrow
    }
  }

  static void Fail()
  {
    throw new InvalidOperationException("fail");
  }

  public static void Main(string[] args)
  {
    try { BadRethrow(); }
    catch (Exception ex)
    {
      Console.WriteLine("Bad: " + (ex.StackTrace == null ? "no stack" : "stack reset likely"));
    }

    try { GoodRethrow(); }
    catch (Exception ex)
    {
      Console.WriteLine("Good: preserves original stack");
    }
  }
}