Unit2_2.pptx Chapter 2 Introduction to C#

M. SC. (Computer Science)
Course Code : 23CsCmpP121
Course Name : DOT NET
PresentedBy : Priyanka Jadhav
Modern College of Arts,Science and Commerce ,Pune-5

Notes
Chapter 2
Introduction to C#

i.
Chapter 2
Introduction to C#
2.1.3 Functions, Delegates
Delegates
What is delegate?
In C#, delegate is a reference to the method. It works
like function pointer in C and C++. But it is objected-
oriented, secured and type-safe than function pointer.
For static method, delegate encapsulates method only.
But for instance method, it encapsulates method and
instance both.
The best use of delegate is to use as event.
Internally a delegate declaration defines a class which is the
derived class of System.Delegate.

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Chapter 2
Introduction to C#
Delegates
A delegate is similar to a class .you can create an
instance of it, and when you do so, you pass in the
function name as a parameter to the delegate
constructor, and it is to this function the delegate will
point to .
Tip to remember delegate syntax -:
delegate syntax look very much similar to a
method with a delegate keyword.

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Chapter 2
Introduction to C#
Delegates
Declaring Delegates
 Delegates in c# are declared using the delegate
keyword followed by the return type and
parameter of the referenced method.
 Declaring a delegate is quite similar to declaring
a method except that there is no implementation.
Thus , the declaration statement must end with a
semicolon.
public delegate int Calculation(int num1,int num2);

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Chapter 2
Introduction to C#
Delegates
Note:-if the delegate is declared outside the class, you
cannot declare another delegate with the same name in
that namespace.
Delegates are called as type safe function
pointer.

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Chapter 2
Introduction to C#
Delegates
Types of Delegate:-
1. Single delegate
2. Multicast delegate
3. Generic delegate

i.
Chapter 2
Introduction to C#
Delegates
1. Single delegate:-
 Single cast delegate can be used to
invoke a single method.
 Single cast delegate point to single
method at a time.
 In this the delegate is assigned to a
single method at a time.

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Chapter 2
Introduction to C#
Delegates
2. MultiCast Delegate:-
 A Multicast delegate is a delegate
that has references to more than one
function.
 When you invoke a multicast
delegate, all the functions the
delegate is pointing to, are invoked.

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Chapter 2
Introduction to C#
There are 2 approaches to create a multicast delegate,
depending on the approach you use :-
 + or += to register a method with the delegate (adding
new method on existing delegate instance)
 -or -= to un-register a method with the delegate .
( can be used to remove a method from a delegate
instance. )
Note-A multicast delegate, invokes the methods in the
invocation list, in the same order in which they are
added.
Delegates

to be cont…
Chapter 2
Introduction to C#
2.1.4 Debugging and error handling, exception
handling( System Defined and User Defined)
Error Handling
Error handling is the process of responding to and
recovering from error conditions in your program.
The errors your program will encounter can be classified in
two categories:-
1. Syntax Errors
2. Logic Errors

to be cont…
Chapter 2
Introduction to C#
Error Handling
Syntax Errors
Syntax Errors occur in program due to poor understanding
of language syntax or mistake while typing.
Few examples of syntax errors in program are missing
semicolon at the end of statement, using reserved
errors as user defined identifiers ,using variable
without declaration etc.

Chapter 2
Introduction to C#
Error Handling
Logic Errors
Logic Errors occur due to improper implementation
of program logic. Compiler does not show any logic
error. If there is any logic error in the program then
program gives wrong results. Logic errors are difficult
to spot.

Chapter 2
Introduction to C#
Debugging
Debugging is the routine process of locating and
removing computer program bugs, errors or
abnormalities, which is methodically handled by
software programmers via debugging tools.
The Debugging is the program you used to debug
your code . The code or application that your are
debugging is called debugger.

Chapter 2
Introduction to C#
Exception Handling
Exception Handling is abnormal events that prevent a certain
task from being completed successfully.
Or in other word - It is process of responding to unwanted or
unexpected events when a computer program runs.
Exceptions are run-time errors that may cause a program to be
immediately terminated. Exception handling is a process of
handling these run-time errors. Handling an exception refers to
the action to be taken when an error occurs in order to save the
program from being prematurely terminated.

Chapter 2
Introduction to C#
Exception Handling
For example:-consider a c# application that is
currently being executed. Assume that at some point
of time, the common language run-time(CLR)
discovers they it does not have the read permission to
read a particular file, the CLR immediately stops
further processing of the program and terminates its
execution abruptly. To avoid this from happening, you
can use the exception handling features of c#.

Chapter 2
Introduction to C#
Exception Handling
C# can handle different types of exceptions using
exception handling statements. It allows you to handle
basically two kinds of exceptions.
These are:
System Defined Exceptions
User Defined Exceptions

Chapter 2
Introduction to C#
Exception Handling
The System.Exception class is the base class that allows you to
handle all exception c#. This means that all exception in c# inherit
the System.Exception class either directly or indirectly.
The system.Exception class contains public and protected method
that can be inherited by other exception class. In addition, the
System.
Exception class contains properties that are common to all
exceptions. The table shown alongside describe these properties.

Chapter 2
Introduction to C#
Exception Handling
Properties of Exception Class
Properties Descriptions
Message Display a message which indicates the
reason for the execution.
Source Provides the name of the application or the
object that caused the exception.
StackTrace Provides exception details on the stack at
the time the exception was thrown.

Chapter 2
Introduction to C#
Exception Handling
Exceptions Description
System.ArithmeticException This expt. Is thrown for problems that occur
due to arithmetic or casting and conversion
operations.
System.ArgumentException This expt. Is thorn when one of the arguments
does not match the parameter specifications
of the invoked method.
System.ArrayTypeMismatchException This exception is thrown when an attempt is
made to store data in an array whose type is
incompatible with the type of the array.

Chapter 2
Introduction to C#
Exception Handling
System.DvideByZeroException
System.IndexOutOfRangeException
System.InvalidCastException
System.ArgumentNullExcption
This exception is thrown when an attempt is
made to divide a numeric value by zero.
This exception is thrown when an attempt is
made to store data in an array using an
index that is less than zero or outside the
upper bound of the array.
This exception is thrown when an explicit
conversion from the base type or interface
type to another type fails.
This exception is thrown when a null
reference is passed to an argument of
method that does not accept null values.
System.NullReferenceException The exception is thrown when you try to
assign a value to a null object.
System.OutOfMemoryException This exception is thrown when there is not
enough memory to allocate to an object.
System.OverflowException This exception. Is thrown when the result of
an ariththmetic,casting or conversion
operation is too large to be stored in the
destination object or variable.

Chapter 2
Introduction to C#
Exception Handling
System.StackOverflowException This exception is thrown when the stack
runs out of space due to having too many
pending method calls.
System.data.DataException This exception Is thrown when errors are
generated while using the ADO.NET
components.
System.FormatException This exception is thrown when the format of
an argument does not match the format of
the parameter data type of the invoked
method.
System.OverflowException This exception. Is thrown when the result of
an ariththmetic,casting or conversion
operation is too large to be stored in the
destination object or variable.
Syste.IO.IOEXception This exception is thrown when any I/O error
occurs while accessing information using
streams , files and directories.

Chapter 2
Introduction to C#
Exception Handling
Catching Exceptions:-
Consider a group of boys playing throw ball wherein one boy throws
a ball and the other boys catch the ball. If any of the boys fail to
catch the ball, the game will be terminated. Thus the game does on
till the boys are successful in catching the ball in time.
Similarly, in c# exception that occur while working on particular
program need to be caught by exception handlers. If the program
does not contain the appropriate exception handler , then the
program might be terminated.

Chapter 2
Introduction to C#
Exception Handling
Catching Exceptions:-
Exception handling is implemented using try-catch construct in c#. This
construct consist of two blocks, the try block and the catch block.. The try
block encloses statements that might generate exceptions. When these
exceptions are thrown, the required actions are perform using the catch
block. Thus the catch block consist of the appropriate error-handlers that
handle exception.
The catch block follows the try block and may or may not contain
parameters. If the catch block does not contain any parameter, it can catch
any type of exception, if the catch block contains a parameter , it catches
the type of exception specified by the parameter.

Chapter 2
Introduction to C#
Exception Handling
The following syntax is used for handling errors using the try and
catch blocks.
try
{
//statements that might raise exception or program code
}
catch(Exceptionclass objException)
{
//statements for handling the exception
}
Note:-the catch block is only executed if the try block throws an
exception.

Chapter 2
Introduction to C#
Exception Handling
The “throw” Statement:-
The throw statement in c# allows you to programmatically throw
exceptions using the throw keyword.
The throw statement takes an instance of the particular exception
class as a parameter. However , if the instance does not refer to the
valid exception class, the c# compiler generates an error.
When you an exception using the throw keyword, the exception is
handled by the catch block.

Chapter 2
Introduction to C#
Exception Handling
The “finally” Statement:-
In general, if any of the statements in the try block raises an
exception, the catch block is executed and the rest of the statement
in the try block are ignored. But , sometimes it becomes mandatory
to execute some statements irrespective of whether an exception is
raised or not. In such cases, a finally block is used.
Examples of action that can be placed in a finally block are: closing a
file, assigning object to null, closing a database connection and so
forth.
The finally block is an optional block appears after the catch block.
It enclose statements that are executed regardless of whether an
exception occurs.

Chapter 2
Introduction to C#
Exception Handling
Nested “try” blocks
The nested try block consists of multiple try-catch constructs. A
nested try block starts with a try block, which is called the outer try
block. This outer try block contains multiple try blocks within it,
which are called inner try blocks. If an exception is thrown by a
nested try block, the control passes to its corresponding nested
catch block.
consider an outer try block containing a nested try-catch –finally
construct. If the inner try block throws an exception, control is
passed to the inner catch block, however, if the inner catch block
does not contain the appropriate error handler, the control is passed
to the out catch block.

Chapter 2
Introduction to C#
Exception Handling
Nested “try” blocks
The following syntax is used to create nested try-catch blocks.
try
{
//outer try block
try
{
//inner try block
}
catch
{
//inner catch block
}
//this is optional
finally
{
//inner finally block
}
}
catch
{
//outer catch block
}
}

Unit2_2.pptx Chapter 2 Introduction to C#

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