InnerExceptions.cs

using System;
using System.IO;


/* Inner Exception Notes
 * 
 * The InnerException property returns the Exception instance that caused the current exception
 * 
 * To retain the original exception, pass it as a parameter to the constructor of the current exception
 * 
 * Always check if the inner exception is not null before accessing any property of the inner exception object -- else, you may get a Null Reference Exception
 * 
 * To get the type of InnerException, use the GetType() method
 * 
 * If you want to intentioanlly throw an exception, you use the 'throw' keyword
 * 
 * 
 * !@!@ Interview Questions !@!@
 * Q. What is an inner exception?
 * A. The InnerException property returns the Exception instance that caused the current exception. 
 *    The InnerException will actually give you the original exception which caused the current exception.
 *    For this to happen, you need to pass the original exception as a parameter to the constructor of the current exception object
 */

class Program
{
    public static void Main()
    {
        try
        {
            try
            {
                Console.WriteLine("Enter the first number: ");
                int firstNumber = Convert.ToInt32(Console.ReadLine());
                //read the user input string, convert to an int, and store it in a variable, firstNumber

                Console.WriteLine("Enter the second number: ");
                int secondNumber = Convert.ToInt32(Console.ReadLine());
                //read the user input string, convert to an int, and store it in a variable, secondNumber

                int result = firstNumber/secondNumber;

                Console.WriteLine("Result = {0}", result);
            }
            catch (Exception exception) //the first caught exception
            {
                string filePath = @"C:\SampleFiles\Log.txt";

                if (File.Exists(filePath))
                {
                    StreamWriter sw = new StreamWriter(filePath);
                    sw.Write(exception.GetType().Name + " - " + exception.Message); //write exception type and message to Log.txt
                    sw.Close();
                    Console.WriteLine("There was a problem. Check the Log.txt file.");
                }
                else
                {
                    throw new FileNotFoundException(string.Format("{0} does not exist.", filePath), exception);
                    //this will retain the information from the original exception by passing in the 'exception' object as a parameter to the FileNotFoundException object
                    //in other words, the original exception is sent to the constructor of the current exception
                }
            }
        }
        catch (Exception exception) //the current caught exception
        {
            Console.WriteLine("Current Exception: {0} ", exception.GetType().Name);
            
            if (exception.InnerException != null) //if the inner exception is null, don't print
            {
                Console.WriteLine("Inner Exception: : {0}", exception.InnerException.GetType().Name);
            }
        }

        Console.ReadKey();
    }
}