/*
Concepts:
. What are exceptions?
. Source of exceptions
	. Illegal user inputs (e.g. FormatException)
	. Programming errors (e.g. IndexOutOfBoundException)
	. System problems (e.g. OutOfMemoryException)
. What can we do with an exception?
	. Catch it (try, catch): we want to handle
		. Do not rethrow: the exception should not disrupt the normal execution
		. Rethrow: the program should be disrupted, but we want to do something before that
	. Let the caller handle it: we don't want to handle/ we don't know how to handle
	. Finally: always execute (e.g. to release resources)
. Can selectively handle some classes of exceptions
. Actively throw exceptions (did not have time to cover)
*/


using System;

public class ExceptionConcepts
{
	public static void Main()
	{
		//IllegalUserInputs();
		//ProgrammingErrors();
		//SystemProblems(1000000);
		//CatchWithoutRethrow();
		//CatchAndRethrow1(null);
		//CatchAndRethrow2(null);
		//ActiveThrow1(1, 0);
		//ActiveThrow2(1, 0);
	}

	static void IllegalUserInputs()
	{
		Console.Write("Please enter an integer: ");
		int i = int.Parse(Console.ReadLine());
	}

	static void ProgrammingErrors()
	{
		int[] a = new int[5];
		for (int i=0; i<=5; i++)
			a[i] = i;
	}

	static void SystemProblems(int i)
	{
		if (i > 0)
			SystemProblems(i-1);
	}

	static void CatchWithoutRethrow()
	{
		int i = 0;
		while (i <= 0)
		{
			try
			{
				Console.Write("Please enter a positive integer: ");
				i = int.Parse(Console.ReadLine());
				if (i <= 0)
					Console.WriteLine("Sorry, the number is non-positive.");
			}
			catch (FormatException e)
			{
				Console.WriteLine("Sorry, it is not a valid integer.");
			}
		}
	}

	static int CatchAndRethrow1(string s)
	{
		try
		{
			int i = s.Length;
			return i;
		}
		catch(NullReferenceException e)
		{
			Console.WriteLine("null parameter is not allowed.");
			throw e;
		}
	}

	static int CatchAndRethrow2(string s)
	{
		try
		{
			int i = s.Length;
			return i;
		}
		catch(NullReferenceException e)
		{
			throw new NullReferenceException("null parameter is not allowed.", e);
		}
	}

	static int ActiveThrow1(int numerator, int denominator)
	{
		return numerator / denominator;
	}

	static int ActiveThrow2(int numerator, int denominator)
	{
		if (denominator == 0)
			throw new DivideByZeroException("Denominator parameter of ActiveThrow2 should not be zero.");
		else
			return numerator / denominator;
	}
}