C# EXCEPTION HANDLING

An exception is a problem that arises during the execution of a program. A C# exception is a response to an exceptional circumstance that arises while a program is running, such as an attempt to divide by zero.

Exceptions provide a way to transfer control from one part of a program to another. C# exception handling is built upon four keywords: try, catch, finally, and throw.

• try: A try block identifies a block of code for which particular exceptions is activated. It is followed by one or more catch blocks.
• catch: A program catches an exception with an exception handler at the place in a program where you want to handle the problem. The catch keyword indicates the catching of an exception.
• finally: The finally block is used to execute a given set of statements, whether an exception is thrown or not thrown. For example, if you open a file, it must be closed whether an exception is raised or not.
• throw: A program throws an exception when a problem shows up. This is done using a throw keyword.

Exception Classes in C#

C# exceptions are represented by classes. The exception classes in C# are mainly directly or indirectly derived from the System.Exception class. Some of the exception classes derived from the System.Exception class are the System.ApplicationException and System.SystemException classes.

The following table provides some of the predefined exception classes derived from the Sytem.SystemException class:

Handling Exceptions

C# provides a structured solution to the exception handling in the form of try and catch blocks. Using these blocks the core program statements are separated from the error-handling statements.

using System;
namespace ErrorHandlingApplication
{
    class DivNumbers
    {
        int result;
        DivNumbers()
        {
            result = 0;
        }
        public void division(int num1, int num2)
        {
            try
            {
                result = num1 / num2;
            }
            catch (DivideByZeroException e)
            {
                Console.WriteLine("Exception caught: {0}", e);
            }
            finally
            {
                Console.WriteLine("Result: {0}", result);
            }
        }
        static void Main(string[] args)
        {
            DivNumbers d = new DivNumbers();
            d.division(25, 0);
            Console.ReadKey();

            //Exception caught: System.DivideByZeroException: Attempted to divide by zero.
            //at...
            //Result: 0
        }
    }
}

Creating User-Defined Exceptions

You can also define your own exception. User-defined exception classes are derived from the ApplicationException class. The following example demonstrates this:

using System;
namespace UserDefinedException
{
    class TestTemperature
    {
        static void Main(string[] args)
        {
            Temperature temp = new Temperature();
            try
            {
                temp.showTemp();
            }
            catch (TempIsZeroException e)
            {
                Console.WriteLine("TempIsZeroException: {0}", e.Message);
            }
            Console.ReadKey();
        }
    }
}
public class TempIsZeroException : SystemException
{
    public TempIsZeroException(string message) : base(message)
    {
    }
}
public class Temperature
{
    int temperature = 0;
    public void showTemp()
    {
        if (temperature == 0)
        {
            throw (new TempIsZeroException("Zero Temperature found"));
        }
        else
        {
            Console.WriteLine("Temperature: {0}", temperature);
        }
    }
}