The document discusses exception handling in C#. It describes how exceptions provide a way to transfer control when errors occur. It explains the try, catch, finally, and throw keywords used in exception handling and provides examples of handling different types of exceptions using these keywords. It also discusses user-defined exceptions and how to create custom exception classes by inheriting from the Exception class.

1. Hello friends
C# Tutorial
Part : 43
Exception Handling
www.siri-kt.blogspot.com

2. • Exception Handling in C# is a process to handle runtime
errors. We perform exception handling so the normal
flow of the application can be maintained even after
runtime errors.
• 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.
• In C#, exception is an event or object which is thrown
at runtime. All exceptions the derived
from System.Exception class.
• It is a runtime error which can be handled. If we don't
handle the exception, it prints exception message and
terminates the program.

3. • 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.

4. • Syntax
• Assuming a block raises an exception, a method catches an
exception using a combination of the try and catch keywords.
• A try/catch block is placed around the code that might generate an
exception. Code within a try/catch block is referred to as
protected code, and the syntax for using try/catch looks like the
following:
• try {
• // statements causing exception }
• catch( ExceptionName e1 ) { // error handling code }
• catch( ExceptionName e2 ) { // error handling code }
• catch( ExceptionName eN ) { // error handling code }
• finally { // statements to be executed }
• You can list down multiple catch statements to catch different type
of exceptions in case your try block raises more than one exception
in different situations.

5. • 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
theSystem.ApplicationException and System.SystemEx
ception classes.
• The System.ApplicationException class supports
exceptions generated by application programs. Hence
the exceptions defined by the programmers should
derive from this class.
• The System.SystemException class is the base class for
all predefined system exception.
• The following table provides some of the predefined

6. Exception Description
System.DivideByZeroExcep
tion
handles the error generated by dividing a number with
zero.
System.NullReferenceExcep
tion
handles the error generated by referencing the null
object.
System.InvalidCastExceptio
n
handles the error generated by invalid typecasting.
System.IO.IOException handles the Input Output errors.
System.FieldAccessExcepti
on
handles the error generated by invalid private or
protected field access.

7. • C# try/catch
• In C# programming, exception handling is performed by try/catch
statement. The try block in C# is used to place the code that may throw
exception. The catch block is used to handled the exception. The catch
block must be preceded by try block.
• C# example without try/catch
• using System;
• public class ExExample
• { public static void Main(string[] args)
• { int a = 10;
• int b = 0;
• int x = a/b;
• Console.WriteLine("Rest of the code");
• } }
• Output:
• Unhandled Exception: System.DivideByZeroException: Attempted to divide

8. • C# try/catch example
• using System;
• public class ExExample
• { public static void Main(string[] args)
• { try
• { int a = 10;
• int b = 0;
• int x = a / b; }
• catch (Exception e) { Console.WriteLine(e); }
• Console.WriteLine("Rest of the code");
• } }
• Output:
• System.DivideByZeroException: Attempted to divide by zero. Rest
of the code

9. • C# finally
• C# finally block is used to execute important code which is to be executed whether
exception is handled or not. It must be preceded by catch or try block.
• C# finally example if exception is handled
• using System;
• public class ExExample
• { public static void Main(string[] args)
• { try
• { int a = 10;
• int b = 0;
• int x = a / b; }
• catch (Exception e) { Console.WriteLine(e); }
• finally { Console.WriteLine("Finally block is executed"); }
• Console.WriteLine("Rest of the code");
• } }
• Output:
• System.DivideByZeroException: Attempted to divide by zero. Finally block is
executed Rest of the code

10. • C# finally example if exception is not handled
• using System;
• public class ExExample
• { public static void Main(string[] args)
• { try
• { int a = 10;
• int b = 0;
• int x = a / b; }
• catch (NullReferenceException e) { Console.WriteLine(e); }
• finally { Console.WriteLine("Finally block is executed"); }
• Console.WriteLine("Rest of the code");
• } }
• Output:
• Unhandled Exception: System.DivideBy

11. • C# User-Defined Exceptions
• C# allows us to create user-defined or custom exception. It is used
to make the meaningful exception. To do this, we need to inherit
Exception class.
• C# user-defined exception example
• using System;
• public class InvalidAgeException : Exception
• { public InvalidAgeException(String message)
• : base(message)
• { } }
• public class TestUserDefinedException
• {
• static void validate(int age)
• { if (age < 18)
• { throw new InvalidAgeException("Sorry, Age must be
greater than 18");

12. • public static void Main(string[] args)
• { try
• { validate(12); }
• catch (InvalidAgeException e) { Console.Write
Line(e); }
• Console.WriteLine("Rest of the code");
• } }
• Output:
• InvalidAgeException: Sorry, Age must be greater

13. For more visit our website www.siri-kt.blogspot.com
Thanks for
Watching
More Angular JS TutorialsMore C sharp (c#) tutorials