Programming in c#

What is C#?
 Is a compute-programming language developed by
Microsoft Corporation, USA.
 Is fully object-oriented language.
 Is first Component-oriented language.
 Suitable for developing Web-based applications
 Designed for developing robust, reliable & durable
components to handle real-world applications.

Highlights of C#
 Derived from C/C++ family.
 It simplifies & modernizes C++.
 It is only component oriented language available today.
 It is a language designed for the .NET Framework.
 It is a concise, lean & modern language.
 It combines the best features of many commonly used
languages: the productivity of VB, the power of C++, & the
elegance of Java.
 It is intrinsically object-oriented & web-enabled.
 It has a lean & consistent syntax.
 Is simple, robust & productive.
 Major parts of .NET Framework are actually coded in C#.

Why C# ?????
 The primary motivation while developing any language is the concern that it able to
handle the increasing complexity of programs that are robust, durable &
maintainable.
 The history of major languages developed is as follows:
BPCL B
C
C++
ANSI C
Oak
Java
ANSI C++
C#
1967 1970
1972
1983
1987
1991
1995
1996
2000
Dennis Ritchie
Bjarne Stroustrup
ANSI Committee
James Gostling
Sun MicroSystems
ANSI Committe
Microsoft
Martin Richards Ken Thompson

Cont….
 C & C++ languages suffer from a
number of shortcomings in
meeting World Wide Web
requirements & standards.
 Some are as follows:
1. The high complexity of language
2. They are not truly object
oriented
3. They have poor type safety
4. They are not suitable for
working with new web
technologies.
5. They do not support versioning
6. Their low productivity
7. They are weak in consistency
8. Their poor compatibility with
the existing systems
 VB, a language promoted by
Microsoft for overcoming these
problems, is not truly object-
oriented and becomes
increasingly difficult to use when
systems become large.
 Java which is truly object-
oriented has not retained some
powerful C++ features such as
operator overloading.
 Java also lacks inter-operability
with code developed in other
languages.
 Microsoft therefore decided to
design a new language.
 The result is C#, a simple &
modern language that directly
addresses the needs of
component-based software
development.

Evolution of C#
 The Internet is the mainstream
for many business organization
today.
 There were a number of
limitations in using the WWW
over the Internet:
1. We could see only one site at a
time
2. The site had to be authored to our
hardware environment
3. The information was basically
read-only.
4. We could not dynamically
compare similar information
stored on different sites.
5. The internet is a collection of
many information islands that do
not co-operate with each other.
 Microsoft wanted to develop a
software platform which will
overcome these limitations &
make the Web both
programmable and intelligent.
 The outcome is a new generation
platform called .NET.
 Microsoft introduced C# as a de
facto language of the .NET
platform.
 C# has been particularly designed
to build software components
for .NET and it supports key
features of .NET natively.
 C# compiler is embedded into
.NET as shown below:
.NET Framework
.NET Platform
C#

Cont…
 C# is a descendant of C++ which in turn is a
descendant of C as illustrated below:
C
C++
Java C# VB
Concept
ProductivityElegance
Concept
Component
Orientation
Object
Orentation
Power

Characteristics of C# (5 marks)
 Simple
 C# simplifies C++ by eliminating irksome operators such as ->, ::, and pointers.
 C# treats integers & Boolean data types as entirely different types.
 Consistent
 C# supports an unified type system which eliminates the problem of varying ranges of
integer types.
 All types are treated as objects.
 Modern
 C# is called modern language bcoz it supports:
 Automatic garbage collection
 Rich intrinsic model for error handling
 Decimal data types for financial applications
 Modern approach to debugging
 Robust security model
 Object-Oriented
 C# is truly object-oriented. It supports:
 Encapsulation
 Inheritance
 Polymorphism

Cont….
 Type-Safe
 Type safety promotes robust programs.
 C# incorporates number of type-safe measures:
 All dynamically allocated objects & arrays are initialized to zero
 Use of any uninitialized variables produces an error message by the compiler
 Access to arrays are range-checked
 C# does not support unsafe casts
 C# supports automatic garbage collection
 Versionable
 Making new versions of software modules work with the existing applications is
known as versioning
 C# provides support for versioning with the help of new & override keywords.
 Compatible
 C# enforces the .NET common language specifications & therefore allows inter-
operation with other .NET languages
 Interoperable
 C# provides support for using COM objects, no matter what language was used to
author them.
 Fexible
 We may declare certain classes & methods as ‘unsafe’ and then use pointers to
manipulate them.

Applications of C#
 C# is a new language developed exclusively to
suit the features of .NET platform.
 It can be used for a variety of applications that
are supported by the .NET platform
 Console applications
 Windows applications
 Developing Windows Controls
 Developing ASP .NET Projects
 Creating Web Controls
 Providing Web Services
 Developing .NET component library

How Does C# differs from C++ ?
 Changes Introduced
1. C# compiles straight from source code to executable
code, with no object files
2. In C#, class definition does not use a semicolon at
end
3. The first character of Main() function is capitalized
4. C# does not support #include statement
5. C# does not support multiple code inheritance
6. Casting in C# is much more safer then C++
7. C# does not support default arguments
8. C# permits declaration of variables between goto &
label

How Does C# differs from C++ ?
 C++ Features Dropped
1. Macros
2. Multiple Inheritance
3. Templates
4. Pointers
5. Global Variables
6. Typedef statement
7. Default Arguments
8. Forward Declaration of Classes
 Enhancements to C++
1. Automatic Garbage Collection
2. Versioning Support
3. Strict Type-Safety
4. Properties to access data members
5. Delegates & Events
6. Boxing & Unboxing
7. Web Services

How Does C# differs from Java ?
1. C# has more primitive data types
2. Arrays are declared differently in C#
3. C# supports struct type & Java does not
4. Java does not provide for operator overloading
5. C# provides for better versioning support than Java
6. C# provides static constructors for initialization
7. Java does not directly support enumerations
8. C# uses is operator instead of instanceof operator in
Java
9. C# checks overflows uses checked statements
10. There is no labeled break statement in C#. The goto
statement is used to achieve this.
11. In Java, the switch statement can have only integer
expression, while C# supports either an integer or string
expressions

Chapter : 2
Understanding .NET: The C# Environment

The .NET STRATEGY
 .NET is a software framework that includes
everything required for developing software for
web services.
 It integrates presentation technologies,
component technologies & data technologies on a
single platform so as to enable users to develop
Internet applications.

The Origins of .NET Technology
 The current technology of .NET has gone through three different phases of development:
 OLE technology
 COM technology
 .NET technology
 OLE (Object Linking & Embedding) technology
 Developed by Microsoft to enable easy inter-process communications.
 OLE provides support to achieve following:
 To embed documents from one application into another application
 To enable one application to manipulate objects located in another application
 COM Technology:
 Overcomes the problems of maintaining and testing of software.
 A program can be divided into number of independent components where each one offers a
particular service.
 Each component can be developed & tested independently and then integrated into the main
system.
 This technology is known as Component Object Model (COM) and the software built using COM is
referred to as componentware.
 Benefits:
 Reduces Complexity
 Enhances software maintainability
 Enables distributed development acrossmultiple organizations

The Origins of .NET Technology (cont…)
 .NET Technology
 Is third generation component model
 Provides a new level of inter-operability compared to COM technology
 Inter-module communication is achieved using Microsoft Intermedia
Language (MSIL) or simply IL
 IL allows for true cross language integration
 IL also provides metadata : describes characteristic of data including
datatypes & locations.
 .NET also includes host of other languages & tools that enable us to
develop & implement Web-based applications easily.
Fig : Three generations of component model
OLE Technology
COM Technology
.NET Technology
Interprocess Communication
Intermodule Communication
Intersite Communication
Phase I – Early 1990s
Phase II – 1995
Phase III – Late 1990s

The .NET Framework
.NET Framework
.NET Building .NET Device
Block Services Software
.NET Platform
.NET User
Experience
.NET Infrastructure
& Tools
Visual Studio .NET Experience
.NET Services
.NET Infrastructure & Tools
Windows .NET .NET Framework

The .NET Framework (cont…)
 The .NET framework is one of the tools provided by the .NET
infrastructure & tools component of the .NET platform.
 The .NET framework provides an environment for building, deploying &
running web services & other applications.
 It consists of three distinct technologies:
 Common Language Runtime
 Framework Base Classes
 User & program interfaces(ASP .NET)
Framework Base Classes
.NET Framework
ASP .NET
(Web Services)
Windows Forms
(User Interface)
Common Language Runtime

The Common Language Runtime (CLR)
 Is heat & soul of the .NET framework
 Is responsible for loading & running C#
programs.
 Supports cross-language interoperability.
 Services provided:
 Loading & execution of programs
 Verification of type-safety
 Providing metadata
 Memory management
 Enforcement of security
 Interoperability with other systems
 Managing exceptions & errors
 Debugging

Components of CLR (cont…)
Intermedia Language (IL)
Common Type System
Common Language Runtime
Execution Support Functions
Security
Garbage Collection
Class Loader
Memory Layout

Framework Base Classes
 Allows to implement applications quickly
 The functionality of the base framework classes resides in
the namespace called System
 Provides:
 Input/Output operations
 String handling
 Managing arrays, lists,maps,etc
 Accessing files & file systems
 Accessing the registry
 Security
 Windowing
 Database management
 Drawing
 Managing errors & exceptions
 Connecting to Internet

User & Program Interfaces
 The .NET framework provides the following tools
for managing user & application interfaces:
 Windows forms
 Web forms
 Console applications
 Web Services
 These tools enables users to develop user-friendly
desktop-based as well as web-based applications.

Benefits of the .NET Approach
 The .NET technology provides a number of benefits to
developers & users.
 Some of them are:
 Simpler & faster systems development
 Enhanced built-in functionality
 Many different ways to communicate with the outside
world
 Integration of different languages into one platform
 Easy execution
 Wide range of scalability
 Interoperability with existing applications
 Fewer bugs
 Potentially better performance

Introduction
 C# can be used to develop two categories of
programs:
 Executable application programs &
 Component libraries
 Executable programs are written to carryout
certain tasks & require Main method in one of
the classes.
 Component libraries do not require Main
declaration because they are not standalone
application programs.
 They are written for use by other applications.

A Simple C# Program
class SampleOne
{
public static void Main()
{
System.Console.WriteLine(“C# is sharper than C++”);
}
}
 Executing the program
 Save the above file with SampleOne.cs name
 Compile as : csc SampleOne.cs
 C# compiler compiles your code and create an executable
file by name
 SampleOne.exe
 For executing the program, simply type in the name of the
executable file at the command prompt.

NAMESPACES
System.Console.WriteLine();
 Here System is a namespace in which the Console class is
located.
 This class can be accessed using the dot operator.
 C# supports using directive that can be used to import the
namespace System into the program.
using System;
class SampleTwo
{
{
Console.WriteLine(“Hello World!!!”);
}
}

Adding Comments
 Enhances readability & understanding of the
code.
 Programs should have information such as
implementation details, change history and tasks
performed.
 Types of comments:
 Single-line comments (//)
 Multiline comments (/* ….. ….. */)

Main Returning a Value
 Main() can also return a value if it is declared as int instead of
void.
 When the return type is int, we must include a return statement
at the end of the method.
using System;
class SampleThree
{
public static int Main()
{
Console.WriteLine(“Hello World!!!”);
return 0;
}
}
 The value returned serves as the program’s termination status
code.
 It allows communication of success or failure to the execution
environment.

Using Aliases for NAMESPACE Classes
using A=System.Console;
class SampleFour
{
{
A.WriteLine(“Hello World!!!”);
}
}

Passing String Objects to WriteLine Method
using System;
class SampleFive
{
{
string name=“PentaSoft Technologies”;
Console.WriteLine(name);
}
}

Command Line Arguments
 Can be used to take an input from a user.
 Command line arguments are parameters supplied to the
Main method at the time of invoking it for execution
using System;
class SampleSix
{
public static void Main(string[] args)
{
string name=“Welcome to”;
Console.Write(name);
Console.Write(“ ”+args[0]);
Console.WriteLine(“ ”+args[1]);
}
}

MAIN with a Class
class Demo //class definition
{
public void display()
{
System.Console.WriteLine(“In Demo Class”);
}
}
class SampleSeven
{
{
Demo d=new Demo(); //creating d object
d.display(); //callinf display() function
}
}

Providing Interactive Input
using System;
class SampleEight
{
{
Console.Write(“Enter Your Name”);
string name=Console.ReadLine();
Console.WriteLine(“Hello ”+name);
}
}

Using Mathematical Functions
using System;
class SampleNine
{
{
double x=5.0;
double y;
y=Math.Sqrt(x);
Console.WriteLine(“y = ”+y);
}
}

Multiple Main Methods
 In C# it is possible to have Main
method in different classes.
 In such situations there would be
multiple entry points in the
program.
 There should be only one.
 This problem can be resolved by
specifying which Main is to be
used to the compiler at the time
of compilation:
 csc filename.cs/main:classname
 Example :
 multimain.cs/main:Class
OR
 multimain.cs/main:Class B
//multimain.cs
using System;
class A
{
{
Console.Write(“Class A”);
}
}
class B
{
{
Console.Write(“Class B”);
}
}

Compile Time Errors
 A program is never totally error-free
 Types of errors:
 Syntax Errors
 Logic Errors
 Syntax errors will be caught by the
compiler
 Logical errors should be eliminated by
testing the program logic carefully.
 When the compiler cannot interpret
what we are attempting to convey
through our code the result is syntax
error.
 Example:
using Systom;
class SampleTen
{
public static void main()
{
Console.Write(“Hello”);
}
}
 Errors.cs(2.7): error cs0234: The type
or namespace name ‘Systom’ does not
exists in the class or namespace
 The error message contains:
1. Name of the file being
compiled(Errors.cs)
2. Line number & column position of the
error(2.7)
3. Error code as defined by the compiler
(cs0234)
4. Short description of error

Program Structure
 The documentation section
consists of a set of comments
giving the name of the
program, the author, date &
other details.
 The using directive section
includes all those namespaces
that contain classes required
by the application
 A interface is similar to a
class but contains only
abstract classes.Used in
multiple inheritance
 A C# program may contain
multiple class definitions.
 Every C# program requires a
Main method as its starting
point, the class containing the
Main is the essential part of
program.
Documentation Section
Using Directive Section
Interfaces Section
Classes Section
Main Method Section
Optional
Optional
Optional
Optional
Essential

Chapter : 4
Literals, Variables & Data Types

Literals
 Literals are the value constants assigned to
variables in a program.
 C# supports seven types of literals.
 Integral Literals : Decimal & Hexadecimal Integers
 Real Literals
 Boolean Literals :True / False
 Single Character Literals
 String Literals
 Backslash Character Literals : a, b, n, t, , ”

Variables
 Is an identifier that denotes a storage location used to store
data value.
 May take different values at different times during
program execution.
 Name should be meaningful.
 May consist of alphabets, digits & the underscore.
 Conditions:
 Not begin with a digit
 Uppercase & lowercase are distinct
 It should not be a keyword
 White space is not allowed
 Name can be of any length

Data Types
 Every variable in c# is associated with a data type
 Specifies the size and type of values that can be stored
 Types in C#
 Value types
 Reference types
 Pointers
 Values types are stored on stack
 When a value of a variable is assigned to another variable,
the value is actually typed.
 Reference types are stored on heap
 When a value of a variable is assigned to another reference
variable, only the reference is copied.

Taxonomy C# data types
C# Data Types
Value Types Pointers Reference Types
Predefined
Types
User-defined
Types
Predefined
Types
User-defined
Types
•Integers
•Real Numbers
•Booleans
•Characters
•Classes
•Arrays
•Delegates
•Interfaces
•Objects
•Strings
•Enumerations
•Structures

Declarations of Variables
 Variables are names of storage locations.
 Declaration does three things
1. Tells the compiler what the variable name is.
2. Specifies what type of data the variable will hold.
3. The place of declaration decides the scopeof variable.
 Syntax:
 type variable1, variable2,……. variableN

Default Values
 A variable is either explicitly assigned a value or automatically
assigned a default value.
 Following categories of variables are automatically initialized to
their default values.
 Static variables
 Instance variables
 Array elements
Type Default Value
All integer types 0
char type ‘x000’
float type 0.0f
double type 0.0d
decimal type 0.0m
bool type false
enum type 0
All reference type null

Constant Variables
 Variables whose values do not change during the
program execution are known as constants.
 Eg.
 const int Rows=10
 const int Cols=10
 Advantages
 Programs are easier to read & understand
 Programs are easier to modify
 Accidental errors are minimized

Scope of Variables
 It is region of code within which the variable can be accessed.
 Depends on type of the variable and its place of declaration.
 Consider following Eg…
class ABC
{
static int m;
int n;
void fun(int x, ref int y, out int z, int[] a)
{
int j=10;
……..
……..
}
}
 Static variables
 Declared at the class level
 Known as fields or field variables.
 The scope of these variables begins at the place of their declaration & ends when the
Main method terminates.
 The value parameter ‘x’ will exists till the end of fun() method
 The reference & output parameters (y & z) do not create a new storage locations.
 Their scope is same as the underlying variables that are passed as arguments.
 Array element a[0] come into existence when an array instance is created, & cease
to exist when there are no references to that array instance.
 Variables declared inside a method are called local variables.
 Their scope is until the end of block inside which they are declared.

Boxing & Unboxing
 In OOP, methods are invoked with the help of objects.
 Value types such as int & long are not objects, we cannot
use them to call methods.
 C# achieve this through a technique called as boxing.
 Boxing means the conversion of a value type on the stack to
a object type on the heap.
 The conversion from an object type back to a value type is
known as unboxing.

Boxing
 Any type, value or reference can be assigned to an object without an explicit
conversion.
 When a compiler finds a value type where it needs a reference type, it creates an
object ‘box’ into which it places the value of the value type.
 Example:
int m=100;
object om=m; //creates a box to hold m
 This code creates a temporary reference type ‘box’ for the object on heap.
 This can also be done with:
int m=100;
object om=(object)m; //C-style casting
 Here the variable m & om exist but the value of om resides on the heap. The values
are independent of each other.
int m=100;
object om=m;
m=20;
Console.WriteLine(m); //m=20
Console.WriteLine(om); //om=10

Unboxing
 It is the process of converting the object type back to the
value type.
 We can only unbox a variable that has previously been
boxed.
 Unboxing is an explicit operation using C-style casting.
int m=100;
object om=m; //box m
int n=(int)om; //unbox om back to an int
 When unboxing a value, we have to ensure that the value
type is large enough to hold the value of the object.

Chapter : 5
Operators & Expressions

Type of Operators
Arithmetic operators
Relational operators
Logical operators
Assignment operators
Increment & decrement operators
Conditional operators
Bitwise operators
Special operators

Arithmetic Operators
Operator Symbol Action Example
Addition + Adds two
operands
x + y
Subtraction - Subtracts the 2nd
operand with 1st
operand
x – y
Multiplication * Multiplies two
operands
x * y
Division / Divides two
operand
x / y
Modulus % Gives the
remainder when
the operands are
divided.
x % y

Exercise
 Write a program to demonstrate use of all
Arithmetic operators.

Relational Operators.
 Relational operators are used to compare
expressions.
 An expression containing a relational operator
evaluate to either true(1) or false (0).

Relational Operators.
Syntax: (ae-1 relational operator ae-2)
Operator Symbol
Equal ==
Greater than >
Less Than <
Greater than or equal to >=
Less than or equal to <=
Not Equal to !=

Exercise
 Write a program to demonstrate use of relational
operators.

Logical operators
 Logical operators helps a user to combine two or more relational
expressions into a single expression.
Operator Symbol
AND &&
OR ||
NOT !
Bitwise logical AND &
Bitwise logical Or |
Bitwise logical exclusive Or ^

The Assignment Operator:-
 Used to assign the value of an expression to a variable.
 The assignment operator is the equal sign (=).
Syntax : variable = expression;
For e.g. a=b;
 C# also has a set of short assignment operator.
 Syntax: v op=exp
 Here ‘v’ is a variable, ‘exp’ is an expression & ‘op’ is an C# binary operator.
 The operator op= is known as shorthand assignment operator.
 Example:
 x+ = y+1; is same as x=x+(y+1);
 Advantages of shorthand assignment operators:
 Easier to read.
 The statement is more concise
 Results in more efficient code

C# Unary mathematical operators:-
Operator Symbol Action Examples
Increment ++ Increments the
operand by one
++x, x++
Decrement -- Decrements the
operand by one
--x, x--

Prefix and Postfix modes
 When used in prefix mode, the increment and
decrement operators modify their operand before
it’s used.
 When used in postfix mode, the increment and
decrement operators modify their operand after
it’s used.

Exercise:-
 Write a program to demonstrate prefix and
postfix modes.

Conditional Operator
 Is C#’s only ternary operator.
 Takes three operators.
 Syntax : exp1 ? exp2 :exp3;
Here if exp1 evaluates to true, then value of exp2
is assigned else of exp3.
 Eg.
a=10;
b=15;
x = (a > b) ? a :b;

Operator Precedence and Parentheses
 Some rules are needed about the order in which operations are
performed.
 This order, called operator precedence, is strictly spelled out in
‘C# ‘
Operators Relative Precedence
* / % 1
+ - 2

Type Conversion
 Used to convert data of one type to another type.
 Example:
byte b1=10;
byte b2=20;
byte b3=b1+b2;
 Results in an error message because, when we add two
byte values, the compiler automatically converts them into
int types and the result is an integer.
 Hence code should be:
int b3=b1+b2; //no error
 Ways of Type Conversion
 Implicit Conversions
 Explicit Conversions
Type Conversions
Implicit
Conversions
Explicit
Conversions
Arithmetic
Operations
Casting
Operations

Mathematical Functions
 Present in Math class of System Namespace.
 Static Members: E and PI
 Mathematical Methods in Math class:
Method Description
Sin() Sine of an angle in
radians
Cos() Cosine of an angle in
radians
Tan() Tanget of an angle in
radians
Asin() Inverse of Sine
Acos() Inverse of Cosine
Atan() Inverse of Tangent
Sinh() Hyperbolic sine
Cosh() Hyperbolic cosine
Tanh() Hyperbolic tangent
Sqrt() Square Root
Pow() Number raised to a
given power
Exp() Exponential
Log() Natural logarithm
Abs() Absolute value
Min() Lower of two numbers
Max() Higher of two numbers

Exercise:-
 Write a program to find square root of number 25
 Write a program to find minimum between two
numbers 25 & 35 using Math class.

Chapter : 6
Decision Making & Branching

The if Statement
 Is a powerful decision making statement
 Used to control the flow of execution of
statements
 General form:
if (boolean-expression)
{
statement-block;
}
statement-x;

Flowchart of simple if control
boolean
expression
?
Statement
block
Statement-X
Next statement
False
True
Entry
Jumping

Exercise
 Write a program that stores weight & height of
10 person in array & count number of person
with height greater than 170 & weight more than
55.

The IF….. ELSE Statement
 Is an extension of if statement.
 General form:
if (boolean-expression)
{
true-block statement (s);
}
else
{
false-block statement (s);
}
statement-x;

Flowchart of if…else control
boolean
expression
?
True-Block
Statement
Statement-X
Next statement
FalseTrue
Entry
False-Block
Statement

Exercise
 Write a program that counts total of even & odd
numbers stored in an array ‘number’.

Nesting of If….Else Statements
 Used when a series of decisions are involved.
 General form:
if (test condition1)
{
if (test condition2)
{
statement-1;
}
else
{
statement-2;
}
}
else
{
statement-3;
}
statement-x;

Flowchart of nested if….else statements
Test
condition1
?
Statement-3
Statement-X
Next statement
True
False
Entry
Statement-1
Test
condition2
?
Statement-2
TrueFalse

Exercise
 Write a program that finds largest among 3
numbers using nested if..else statement.

The Else If Ladder
 Used when multipath decisions are involved.
 It is an chain of ifs in which the statement associated with each else is an
if.
 General form:
if (condition 1)
statement-1;
else if (condition 2)
statement-2;
else if (condition 3)
statement-3;
else if (condition n)
statement-n;
else
default-statement;
statement-x;

Exercise
 Write a program that finds the grade of a student
using else if ladder.

The Switch Statement
 If statements increases complexity of a
program dramatically as the
alternatives increases.
 The program becomes difficult to read
& follow.
 C# offers an alternative with the help of
switch statement
 General Form:
switch(expression)
{
case value-1:
block-1
break;
case value-2:
block-2
break;
--------------------
--------------------
--------------------
default:
default-block
break;
}
statement-x;
 Here, the expression must be an integer
type or char or string type
 Value-1, value-2 … are constants or
constant expressions & are known as
case labels.
 Block-1, block-2…… are statement lists
and may be zero or more statements.

Example
using System;
class CityGuide
{
public static void main()
{
Console.WriteLine(“Select your choice”);
Console.WriteLine(“London”);
Console.WriteLine(“Bombay”);
Console.WriteLine(“Paris”);
Console.WriteLine(“Type your choice”);
String name = Console.ReadLine ( );
switch (name)
{
case “Bombay”:
Console.WriteLine(“Bombay : Guide 5”) ;
beak;
case “London”:
Console.WriteLine(“london : Guide 10”) ;
beak;
case “Paris”:
Console.WriteLine(“Paris : Guide 15”) ;
beak;
default:
Console.WriteLine(“Invalid choise”) ;
break;
}
}
}

Fallthrough in Switch Statement
 In the absence of the break
statement in a case block, if the
control moves to the next block
without any problem, it is known
as ‘fallthrough’.
 Fallthrough is permitted in C, C+
+ & Java.
 C# does not permit automatic
fallthrough, if the case block
contains some code.
 However, it is allowed if the case
block is empty.
 If we want two consecutive case
blocks to be executed
continuously, we have to force the
process using the goto statement.
 Example
switch(m)
{
case 1:
x=y;
goto case2;
case 2:
x=y+m;
goto default;
default:
x=y-m;
break;
}

Chapter : 7
Decision Making & Looping

The While Statement
 The process of repeatedly
executing a block of statements is
known as looping.
 Is an entry-controlled loop
statement.
 The test condition is evaluated
and if the condition is true, then
the body of the loop is executed.
 Syntax:
initialization;
while(test condition)
{
Body of the Loop…
}
 Entry based loop
Body of the
loop
Test
cond
True
False

Example
class DowhileTest
{
public static void Main ( )
{
int two,count,y;
two = 2;
count=1;
System.Console.WriteLine("Multiplication Table n");
while(count<=10)
{
y = two * count ;
System.Console.WriteLine("2 * " + count + " = " + y) ;
count = count + 1;
}
}
}

The Do Statement
 On some occasions it might be
necessary to execute the body of
the loop before test is performed
 This can be handled using do
statement.
 Is an exit-controlled loop
statement.
 The body of the loop is executed
at least once.
 Syntax:
initialization;
do
{
Body of the Loop…
}while(test condition);
Body of the
loop
Test
cond
• Exit based loop
False
True

Example
class DowhileTest
{
{
int two,count,y;
two = 2;
count=1;
System.Console.WriteLine("Multiplication Table n");
do
{
y = two * count ;
System.Console.WriteLine("2 * " + count + " = " + y) ;
count = count + 1;
}while ( count <= 10 ) ;
}
}

Exercise
 Program using do..while to print all the odd
numbers till 20

The For Statement
 Is an entry-controlled loop
 Syntax:
for(initialization;testcondition;increment)
{
Body of the loop…..
}
 All the three actions, namely initialization,
testing & incrementing, are placed in the for
statement itself.

Exercise
 Program using for loop to print multiplication
table from 2 to 5

The FOREACH Statement
 Enables to iterate elements in an array.
 General form:
foreach(type variable in expression)
{
Body of the loop
}
 The type & variable declares the iteration variable.
 During execution, iteration variable represents the array
element for which iteration is currently being performed.
 in is a keyword.

Example
using System;
class ForeachTest
{
{
int[] arryInt={11,22,33,44};
foreach(int m in arryInt)
{
Console.Write(" " + m);
}
Console.WriteLine();
}
}

Jumps in Loops
 C# permits a jump from one statement to the end or
beginning of a loop as well as jump out of a loop.
 Jumping Out of a loop
 An early exit from a loop can be accomplished by using the
break & goto statements.
 Using break statement the loop is immediately exited and
the program continues with the statement immediately
following the loop.
 Skipping a Part of a Loop
 The continue statement causes the loop to continue with
the next iteration after skipping any statements in the
between.

while(……….)
{
………………….
……………………
if (condition)
break;
……………..
……………..
}
……………..
for (……….)
{
………………
if (error)
break;
……………..
……………..
}
………………..
Exit from
loop
do
{
……………
………..
if (condition)
break;
…………..
…………..
}while (…………….)
……….
for (……………….)
{
…………
for (………..)
{
…………..
if (condition)
break;
……………
}
……………
}
Exit from
loop
Exit from
loop Exit from
loop
Exiting a loop with break statement

while (test condition)
{
…………
if (………..)
continue;
………….
………….
}
for (initialization; test condition; increment)
{
…………
if (………….)
continue;
…………
…………
}
do
{
………..
if (………..)
continue;
………….
…………..
} while (test condition);
Bypassing & Continuing in Loops

Labelled Jumps
 Used to jump a set of nested loops or to continue a loop
that is outside a current one.
 Example
Public static void Main(String a[])
{
if(a.Length==0)
goto end;
Console.WriteLine(a.Lenght);
end; //Label name
Console.WriteLine(“end”);
}

Declaring Methods
 Methods are declared inside the body of a class
 General form:
modifiers type methodname(formal-parameter-list)
{
method---body
}
 Method declaration has five parts:
 Name of the method
 Type of value the method returns
 List of parameters
 Body of the method
 Method modifiers
 Example:
int Product(int x,int y)
{
int m=x*y;
return(m);
}

Modifier Description
new The method hides an inherited method with the same signature.
public The method can be access from anywhere, including outside the class.
protected The method can be access from within the class to which it belongs, or a type
derived from that class.
internal The method can be accessed from within the same program.
private The method can only be accessed inside the class to which it belongs.
static The method does not operate on a specific instance of the class
virtual The method can be overridden by a derived class.
abstract A virtual method which defines the signature of the method, but doesn’t
provide an implementation.
override The method overrides an inherited virtual or abstract method.
sealed The method overrides an inherited virtual method, but cannot be overridden
by any class which inherit from this class. Must be used in conjunction with
override.
extern The method is implemented externally, in a different language.
List of Method Modifiers

Invoking Methods
 Once method is defined, they must be activated
for operations.
 Process of activating a method is known as
invoking or calling
 General form:
objectname.methodname(actual-parameter-list);

Example
using System;
class Method // class containing the method
{
// Define the Cube method
public int Cube(int x)
{
return(x*x*x);
}
}
// Client class to invoke the cube method
class MethodTest
{
public static void Main( )
{
// Creat object for invoking cube
Method M = new Method( );
// invoke the cube method
int y = M.Cube(5); //Method call
// Write the result
Console.WriteLine(y);
}
}

Program for calling a static method
using System;
class StaticMethod
{
{
double y = Square (2.5F); //Method Call
Console.WriteLine( y );
}
static double Square ( float x )
{
return ( x * x );
}
}

Nesting of Methods
 Methods can be invoked without
using an object & dot operator.
 A method can be called using only
its name by another method of
the same class.
 This is known as nesting of
methods.
using System;
class Nesting
{
public void Largest ( int m, int n )
{
int large = Max ( m , n );
Console.WriteLine( large );
}
int Max ( int a, int b )
{
int x= ( a > b ) ? a : b ;
return ( x );
}
}
class NestTesting
{
{
Nesting next = new Nesting ( ) ;
next.Largest ( 100, 200 ) ;
}
}

Method Parameters
 For managing the process of passing values &
getting back the results, C# employs four kinds of
parameters.
 Value Parameters
 Reference Parameters
 Output Parameters
 Parameter Arrays

Pass By Value
 By default, method
parameters are passed by
value.
 When a method is invoked,
the value of actual
parameters are assigned to
the corresponding formal
parameters.
 Any changes to formal
parameters does not affect
the actual parameters.
 There are 2 copies of
variables when passed by
value.
using System;
class PassByValue
{
static void change (int m)
{
m = m+10;
}
{
int x = 100;
change (x);
Console.WriteLine("x =" +
x);
}
}

Pass By Reference
 We can force the value parameters to
be passed by reference.
 Use ref keyword.
 This does not create a new storage
location.
 It represents the same storage
location as the actual parameter.
 When a formal parameter is declared
as ref, the corresponding actual
argument in the method invocation
must be declared as ref.
 Used when we want to change the
values of variables in the calling
method.
using System;
class PassByRef
{
static void Swap ( ref int x, ref int y )
{
int temp = x;
x = y;
y = temp;
}
{
int m = 100;
int n = 200;
Console.WriteLine("Before Swapping;");
Console.WriteLine("m = " + m);
Console.WriteLine("n = " + n);
Swap (ref m , ref n );
Console.WriteLine("After Swapping;");
Console.WriteLine("n = " + n);
}
}

The Output Parameters
 Used to pass results back to the calling method.
 Declare the parameters with an out keyword.
 It does not create a new storage location.
 When a formal parameter is declared as out, the corresponding actual argument in the method
invocation must also be declared as out.
using System;
class Output
{
static void Square ( int x, out int y )
{
y = x * x;
}
{
int m; //need not be initialized
Square ( 10, out m );
}
}

Variable Argument Lists
 We can define methods that can
handle variable number of
arguments using parameter
arrays.
 Parameter arrays are declared
using the keyword params
 The parameter arrays should be a
one-dimensional arrays.
using System;
class Params
{
static void Parray (params int [ ]
arr)
{
Console.Write("array elements
are:");
foreach ( int i in arr)
Console.Write(" " + i);
Console.WriteLine( );
}
{
int [ ] x = { 11, 22, 33 };
Parray ( x) ; //call 1
Parray ( ) ; //call 2
Parray ( 100, 200 ) ;//call 3
}
}

Method Overloading
 Enables us to create more than one
method with the same name, but with
the different parameter lists &
different definitions.
 Required when methods are required
to perform similar tasks but using
different input parameters.
 Example
using System;
class Overloading
{
{
Console.WriteLine(add(2,3));
Console.WriteLine(add(2.6F,3.1F));
Console.WriteLine(add(312L,22L,21));
}
static int add(int a,int b)
{
return(a+b);
}
static float add(float a,float b)
{
return(a+b);
}
static long add(long a,long b,int c)
{
return(a+b+c);
}
}

Introduction
 Array is a group of contiguous or related data
items that share a common name.
 A particular value is indicated by writing a
number called index number or subscript in
brackets after the array name.
 Example : marks[10]
 The complete set of values is referred to as an
array.
 The individual values are called elements.

One-Dimensional Arrays
 A list of items can be given one variable name using only one subscript &
such a variable is called a one-dimensional array.
 Declaration of Arrays:
 Syntax: type[] arrayname;
 Example: int[] counter;
float[] marks;
int[] x,y;
 Creation of Arrays:
 Syntax: arrayname = new type[size];
 Example: counter=new int[5];
marks=new float[4];
 Combination:
int[] counter=new int[5];
 Initialization of Arrays:
 Syntax: arrayname[subscript]=value;
 Example: marks[0]=60;
marks[1]=70;
int[] counter={10,20,30,40,50};
int len=c.Length; //Returns Length of Array

Exercise
 Write a program to sort an array of 5 number
taking from user as input.

Two-Dimensional Arrays
 Allows to store table of values.
 Example: v[4,5];
 Each dimension of the array is indexed from zero to its
maximum size minus one.
 First index specifies the row & second index specifies the
column within that row.
 Declaration: int[,] myArray;
 Creation: myArray=new int[3,4];
 Combination: int[,] myArray=new int[3,4];
 Initialization: int[,] n={{0,0,0},
{1,1,1}};

Example
using System;
class MulTable
{
static int ROWS = 5;
static int COLUMNS = 10;
{
int[,] product =new int[ROWS,COLUMNS];
int i,j;
for (i=1; i<ROWS; i++)
{
for (j=1; j<COLUMNS; j++)
{
product[i, j] = i*j;
Console.Write(" " +product[i , j]);
}
Console.WriteLine(" ");
}
}
}

Variable-Size Arrays
 C# treats multidimensional arrays as ‘arrays of arrays’.
 It is possible to declare two-dimensional array as follows:
 int[][] x=new int[3][]; //three rows array
 x[0]=new int[2]; //first row has two elements
 x[1]=new int[4]; //second row has four elements
 x[2]=new int[3]; //third row has three elements
 These statements create a two-dimensional array having
different length for each row.
 Also called as jagged arrays.
 Initializing: x[1][1]=10;

System.Array Class
 In C# every array we create is automatically derived from
the System.Array class.
 Methods/properties present in this class:
Method/Property Purpose
Clear() Sets a range of array elements to empty values
CopyTo() Copies elements from source array to destination
array
GetLength() Gives the number of elements in a given
dimension of the array
GetValue() Gets the value for a given index in the array
Length Gets the lengths of an array
SetValue() Sets the value for a given index in the array
Reverse() Reverses the contents of a one-dimensional array
Sort() Sorts the elements in a one-dimensional array.

Example
using System;
class Sort
{
{
int[] x ={10,5,2,11,7};
Console.WriteLine("Before Sort");
foreach(int i in x)
Console.WriteLine(" " + i);
Array.Sort(x);
Console.WriteLine("After Sort");
foreach(int i in x)
Console.WriteLine(" " + i);
}
}

ArrayList Class
 Present in System.Collections namespace.
 Can store a dynamically sized array of objects.
 Has an ability to grow dynamically.
 Example:
 ArrayList city=new ArrayList(30);
 Creates city with a capacity to store 30 objects.
 Default is 16.
 Adding Elements: city.Add(“Delhi”);
city.Add(“Mumbai”);
 Removing Elements: city.RemoveAt(1);
 Modifying Capacity: city.Capacity=20;

Example
using System;
using System.Collections;
class Sort
{
{
ArrayList city=new ArrayList();
city.Add("Delhi");
city.Add("Mumbai");
city.Add("Madras");
city.Add("Kerela");
Console.WriteLine("Capacity=" + city.Capacity);
for(int i=0;i<city.Count;i++)
Console.WriteLine(" " + city[i]);
city.Sort();
Console.WriteLine("After Sort");
for(int i=0;i<city.Count;i++)
Console.WriteLine(" " + city[i]);
}
}

ArrayList Property & Methods
Method/Property Purpose
Add() Adds an object to a list
Clear() Removes all the elements from the list
Contains() Determines if an element is in the list
CopyTo() Copies a list to another
Insert() Inserts an elements into the list
Remove() Removes the first occurrence of an element
RemoveAt() Removes the element at the specified place
RemoveRange() Removes a range of elements
Sort() Sorts the elements
Capacity Gets or sets the number of elements in the list
Count Gets the number of elements currently in the
list.

Chapter : 10
Manipulating Strings

Introduction
 Represents a sequence of characters
 Example : string s1=“abc”’;
 Copying String:
string s2=s1;
string s2=String.Copy(s1);
 Concatenating String:
string s3=s1+s2;
string s3=string.Concat(s1,s2);
 Reading from keyboard:
string s=Console.ReadLine();
 Conversion:
int num=111;
string s=num.ToString();
 Verbatim Strings: Starts with @ symbol. Tells the compiler
to use string as verbatim string even if it includes escapes
characters.
String s1=@”EGBCSharpString.cs”;tim

String Methods
 String objects are immutable.
 Thus we cannot modify the characters contained
in them.
 However we can produce a modified version of a
string using built in operations.
 Methods:
Compare(), Concat(), Copy(), Equals(), Insert(),
Join(), Replace(), Split(), ToLower(), ToUpper(),
Trim(), TrimStart(), TrimEnd().

Example
using System;
class demo
{
{
string s1="Lean";
string s2=s1.Insert(3,"r");
string s3=s2.Insert(5,"er");
string s4="Learner";
string s5=s4.Substring(4);
Console.WriteLine(s2);
Console.WriteLine(s3);
if(s3.Equals(s4))
Console.WriteLine("Two Strings are Equal");
Console.WriteLine("Substring="+s5);
}
}

Mutable Strings
 They cab be modified using StringBuilder class.
 Can grow dynamically.
 Also known as dynamic strings.
 Example:
StringBuilder s=new StringBuilder(“abc”);
 Methods:
Append(), Insert(), Remove(), Replace()
 Property:
Capacity, Length, [ ]

Example
using System;
using System.Text;
class StringBuild
{
{
StringBuilder s=new StringBuilder("Object ");
Console.WriteLine("Original="+s);
Console.WriteLine("Length="+s.Length);
s.Append("Language");
Console.WriteLine("Append="+s);
s.Insert(6," Oriented ");
Console.WriteLine("Inserted="+s);
}
}

Regular Expressions
 Provides a powerful tool for searching & manipulating a
large text.
 Used to:
 Locate substrings & return them
 Modify one or more substrings & return them
 Identify substrings that begin with or end with a pattern of
characters
 Find all words that begin with a group of characters and
end with some other characters
 A regular expression (also known as pattern string) is a
string containing two types of characters,
 Literals
 Metacharacters
 Literals are characters that we wish to search & match in
the text
 Metacharacters are special types of characters that give
commands to the regular expression parser.

Cont….
 Examples of Regular Expression:
Expression Meaning
“bm” Any Word Beginning with m
“erb” Any word Ending with er
“bmS*erb” Any word beginning with m and ending with er
“|,” Any word separated by spaces or comma
System.Text.RegularExpressions supports a number of
classes that can be used for searching, matching &
modifying a text document.

Example
using System;
using System.Text;//for StringBuilder class
using System.Text.RegularExpressions; //for Regex class
class RegexTest
{
{
string str;
str = "Amar, Akbar, Antony are friends!";
Regex reg = new Regex (" |, ");
StringBuilder sb = new StringBuilder( );
int count = 1;
foreach(string sub in reg.Split(str))
{
sb.AppendFormat("{0}: {1}n", count++, sub);
}
Console.WriteLine(sb);
}
}

Chapter : 11
Structures & Enumerations

Structures
 We can create our own value types using structures.
 Used to pack data of different types.
 Syntax: Define Structure
struct struct-name
{
datamember1;
datamember2;
…….
}
 The variables inside struct are called as members or fields or elements.
 Creating variables of new type:
struct-name variablename;
or
struct-name variablename = new struct-name();
 Assigning values to Members:
variablename.datamember1=value;
 Struct data members are private by default & hence declare them as
public.

Example
using System;
struct Item
{
public string name;
public int code;
public double price;
}
class StructTest
{
{
Item fan;
fan.name = "Bajaj";
fan.code = 123;
fan.price = 1576.50;
Console.WriteLine("Fan name: " + fan.name);
Console.WriteLine("Fan code: " + fan.code);
Console.WriteLine("Fan cost: " + fan.price);
}
}

Structs with Methods
 We can also assign values to data members using constructors.
 A constructor is a method which is used to set values of data
members at the time of declaration.
struct Number
{
int number;
public Number (int value)
{
number=value;
}
}
 The constructor is invoked as follows:
Number num=new Number(190);

Example
using System;
struct Rectangle
{
int a, b;
public Rectangle ( int x, int y ) //constructor
{
a = x;
b = y;
}
public int Area( ) //a method
{
return ( a * b );
}
public void Display ( ) //another method
{
Console .WriteLine("Area = " + Area( ) );
}
}
class TestRectangle
{
{
Rectangle rect = new Rectangle ( 10, 20 );
rect.Display ( ); //invoking Display ( ) method
}
}

Difference between Classes & Structs (5 Marks)
Category Classes Structs
Data Type Reference type & stored on
heap
Value Type & stored on
stock
Inheritance Support Inheritance Do Not Support
Inheritance
Default Values Default value of a class
type is null
Default value is the value
produced by ‘zeroing out’
the fields of struct
Field
Initialization
Permit initialization of
instance fields
Do Not
Constructors Permit declaration of
parameterless constructors
Do Not
Destructors Supported Not Supported
Assignment Copies the referennce Copies the value

Enumerations
 Is a user defined integer type.
 Provides ways for attaching names to numbers.
 Enum keyword automatically enumerates list of words by
assigning them values 0,1,2 & so on.
 General Form:
enum Shape
{
Circle,
Square,
Triangle
}
Here Circle has value 0, Square has value 1 & Triangle has
value 2.

Example
using System;
class Area
{
public enum Shape {Circle,Square}
public void AreaShape ( int x, Shape shape)
{
double area;
switch (shape)
{
case Shape.Circle:
area = Math.PI * x * x;
Console.WriteLine("Circle Area = "+area);
break;
case Shape.Square:
area = x * x ;
Console.WriteLine("Square Area = " +area);
break;
default:
Console.WriteLine("Invalid Input");
break;
}
}
}
class EnumTest
{
{
Area area = new Area ( );
area.AreaShape ( 15, Area.Shape.Circle);
area.AreaShape ( 15, Area.Shape.Square);
area.AreaShape ( 15, (Area.Shape) 1 );
area.AreaShape ( 15, (Area.Shape) 10 );
}
}

Chapter : 12
Classes & Objects

Introduction
 C# is a true object oriented language.
 We create objects of a have class that have state
& behavior.
 Object oriented language employ 3 core
principles:
 Encapsulation
 Inheritance
 Polymorphism.

Member Access Modifiers
 OOP provides data hiding
 A class may be designed to hide its members from outside
accessibility.
 This is achieved using access specifiers.
 In C# all members have private access by default.
Modifier Accessibility Control
private Member is accessible only from the class containing the
member.
public Member is accessible from anywhere outside the class as
well. Also accessible in derived class
protected Member is accessible only to its own class & in derived
class.
internal Member is available within the assembly or component
that is being created but not to the clients of that
component.
protected
internal
Available in the containing program & in the derived
class

Objects
 An object in C# is a block of memory that contains space to
store all the instance variable.
 Creating an Object:
Rectangle rect; //declare
rect=new Rectangle(); //instantiate
Or
Rectangle rect=new Rectangle();
 We can create ‘n’ number of objects of a class each having a
different memory storage area.
 Accessing Class Members:
objectname.variablename;
objectname.methodname(parameter-list);

Example
using System;
class Rectangle
{
public int length, width;
public void GetData(int x, int y)
{
length = x;
width = y;
}
public int RectArea( )
{
int area = length * width;
return (area);
}
}
class Rect
{
{
int area1;
Rectangle rect1=new Rectangle();
rect1.GetData(12,10);
area1=rect1.RectArea();
Console.WriteLine("Area="+area1);
}
}

Constructors
 Used to initialize an object when it is
created.
 Have the same name as that of the
class.
 They do not have a return type.
using System;
class Rectangle
{
public Rectangle(int x, int y)
{
length = x;
width = y;
}
public int RectArea( )
{
return (area);
}
}
class Rect
{
{
int area1;
Rectangle rect1=new Rectangle(12,10);
area1=rect1.RectArea();
}
}

Overloaded Constructors
• Constructors with same name as of class butConstructors with same name as of class but
different no. & name of arguments.different no. & name of arguments.
• Also known as polymorphism.Also known as polymorphism.
using System;
class Room
{
public Room(int x, int y)
{
length = x;
width = y;
}
public Room(int x)
{
length = width=x;
}
public int RArea( )
{
return (area);
}
}
class Area
{
{
int area1;
Room r1=new Room(12,10);
Room r2=new Room(12);
area1=r1.RArea();
area1=r2.RArea();
}
}

Static Members
 They are common to all
the objects.
 Are accessed without using
a particular object.
 Also referred as class
variables & class methods.
 A static variable is
common to all instances of
a class.
 Even methods can be
declared as static.
 Restrictions on Static
Methods:
 Can only call other static
methods.
 Can only access static
data.
 Cannot refer to this or
base in any way

Example
using System;
class Mathopt
{
public static float mul(float x, float y)
{
return(x*y);
}
public static float divide(float x, float y)
{
return(x/y);
}
}
class MathApp
{
{
float a=Mathopt.mul(10,20);
float b=Mathopt.divide(20,4);
Console.WriteLine("Multiplication="+a);
Console.WriteLine("Division="+b);
}
}

Static Constructors
 Is called before any object of a class is created.
 Useful to do any housekeeping work that needs to be done once.
 Used to assign initial values to static data members.
 Static constructor do not have any parameters.
 Example:
class Abc
{
static Abc()
{
………
}
}
 A class can have only one static constructor

Copy Constructors
 A copy constructor creates an object by copying
variables from another object.
 Example:
public Item(Item item)
{
code=item.code;
price=item.price;
}
…………
Item item2=new Item(item1);
 Here item2 is an copy of item1.

Destructors
 It is opposite to constructor.
 It is a method called when an
object is no longer required.
 The name of destructor is
same as that of class name &
is preceded by a tilde(~).
 They do not have a return
type.
 They do not take arguments.
 Example:
class Fun
{
…….
~Fun()
{
…..
}
}
 C# manages memory
dynamically & uses a
garbage collector, to execute
all destructors on exit.
 This process is called
finalization.

The This Reference
 This refers to the object that called the method.
 Used to distinguish between local & instance variables that have the same
name.
 Example:
class Integers
{
int x;
int y;
public void SetXY(int x, int y)
{
this.x=x;
this.y=y;
}
…..
…..
}

Constant Members (IMP)
 They are the variables whose value cannot be changed
during program execution.
 Example:
public const int size=100;
 Any attempt to change the value of a constant result in
compilation error.
 The const members are implicitly static.
 Const members are accessed using class name.
 Value must be set when cont is defined.

Read-Only Members (IMP)
 Allows us to decide the value
of a constant member at run-
time.
 Also allows to have different
constant values for different
objects of the class.
 The value of the member is
set using constructor &
cannot be modified later.
 Can be declared as either
static fields or instance fields.
 Example:
class Numbers
{
public readonly int m;
public static readonly int n;
public Numbers(int x)
{
m=x;
}
static Numbers()
{
n=100;
}
}

Properties (IMP)
 In C# private data members can only be accessed using
methods of a class.
 Such methods are called as an accessor methods.
 Drawbacks of using these methods:
 We have to code them manually.
 User have to remember that they have to use accessor
methods to work with data members.
 C# provides ‘properties’ that has same capabilities as of
accessor methods.
 Using property we can access data members as if they are
public.
 Also referred to as smart fields.

Example
using System;
class Number
{
private int number;
public int Anumber
{
get
{
return number;
}
set
{
number=value;
}
}
}
class PropertyTest
{
{
Number n=new Number();
n.Anumber=20;
int m=n.Anumber;
Console.WriteLine("Number="+m);
}
}
 Above class declares a get accessor
method (getter) & a set accessor
method (setter).

Property (cont…)
 A property can omit either a get clause or a set clause.
 A property that has only a getter is called a read-only
property.
 A property that has only a setter is called a write-only
property.
 Other features:
 Properties can also represent dynamic data.
 Properties are also inheritable.
 Can be used with static keyword.

Indexers (IMP)
 Indexers are locations indicators.
 Used to access class objects.
 An indexer looks like a property
& is written like it but with 2
differences:
 The indexer takes an index
argument & looks like an array.
 The indexer is declared using
keyword this.
 Also referred to as smart arrays.
 Difference between indexers &
properties:
 A property can be static
member, whereas an indexer is
always an instance member.
 A get accessor of a property
corresponds to a method with
no parameters, whereas for
indexer it corresponds to same
formal parameter list as the
indexer.
 A set accessor of a property
corresponds to a method with a
single parameter named value,
whereas for indexer it
corresponds to same formal
parameter list as the
indexer,plus the paramter
named value.
 It is an error for an indexer to
declare a local variable with the
same name as an indexer
parameter.

Example
using System;
using System.Collections;
class MyClass
{
private string []data = new string[5];
public string this [int index]
{
get
{
return data[index];
}
set
{
data[index] = value;
}
}
}
class MyClient
{
{
MyClass mc = new MyClass();
mc[0] = “UniqueInfotech";
mc[1] = “18";
mc[2] = “Janardan Arcade";
mc[3] = “Dahanu";
mc[4] = “West";
Console.WriteLine("{0},{1},{2},{3},
{4}",mc[0],mc[1],mc[2],mc[3],mc[4]);
}
}

Chapter : 13
Inheritance & Polymorphism
(IMP)

Introductoin
 Inheritance is a process of constructing or
designing one class from another.
 Forms of Inheritance
 Classical form
 Containment form
Feature X
Feature Y
Feature Z
Feature X
Feature Y
Feature Z
Feature P
Base Class
Derived

Classical Inheritance
 Represents a kind of relationship between two classes.
 Example:
 Here class A is referred to as base class, parent class or
super class.
 Class B is referred to as derived class, child class or sub
class.
 Also referred to as ‘is-a’ relationship.
 Example:
 Dog is-a type of animal
 Ford is-a type of car
Class A
Class B

Different Classical Inheritance Implementation
A
B
A
C
B
A
DCB
A
B
C
Grandparent class
Parent class
Child class
Single Inheritance
Hierarchical
Inheritance
Multiple
Inheritance
Multilevel
Inheritance

Containment Inheritance
 Also known as containership
inheritance.
 Example:
class A
{
….
}
class B
{
….
A a; //a is contained in b
}
B b;
….
 Here object a is contained in
object b.
 This relationship is referred
to as ‘has-a’ relationship.
 The outer class B which
contains the inner class A is
termed the ‘parent’ class &
the contained class A is
termed a ‘child’ class.
 Example:
 Car has-a radio.
 City has-a road.

Defining a Subclass
 Syntax:
class subclass-name : baseclass-name
{
variable declaration;
methods declaration;
}

Example: Simple Inheritance
using System;
class Item
{
public void Company()
{
Console.WriteLine("Item Code=XYZ");
}
}
class Fan:Item
{
public void Model()
{
Console.WriteLine("Model=Classic");
}
}
class SimpleInheritance
{
{
Fan f=new Fan();
f.Company();
f.Model();
}
}

Characteristic of Inheritance
 A derived class extends its direct base class. It can add new
members to those it inherits. However, it cannot change or
remove the definition of an inherited member.
 A derived class can hide an inherited member.
 A derived class can override an inherited member.
 An instance of a class contains a copy of all instance fields
declared in the class & its base class.
 Constructors and destructors are not inherited.

Visibility Control
 Class Visibility :
 A class may be declared as:
 public: Accessible within & outside the program assembly
 internal (default): Accessible only within program assembly
 private: Accessible only within the class.
 Class Members Visibility :
 Can be declared as either:
 public
 private
 protected
 internal
 protected internal
Keyword Visibility
Containing
Classes
Derived
Classes
Containing
Program
Anywhere
Outside the program
Private Y
Protected Y Y
Internal Y Y
P.Internal Y Y Y
Public y Y y Y

Accessibility Constraints
 Constraints on the accessibility of members &
classes when they are used in process of
inheritance:
 The direct base class of a derived class must be at
least as accessible as the derived class itself.
 Accessibility domain of a member is never larger
than that of the class containing it.
 The return type of a method must be as accessible as
the method itself.

Defining Subclass Constructor
using System;
class Room
{
public int length;
public int breadth;
public Room(int x, int y)
{
length=x;
breadth=y;
}
public int Area()
{
return(length*breadth);
}
}
class BedRoom:Room
{
int height;
public BedRoom(int x,int y,int
z):base(x,y)
{
height=z;
}
public int Volume()
{
return(length*breadth*height);
}
}
class InherTest
{
{
BedRoom room1=new
BedRoom(10,11,12);
int area1=room1.Area();
int vol=room1.Volume();
Console.WriteLine("Area= "+area1);
Console.WriteLine("Volume= "+vol);
}
}

Multilevel Inheritance
 Uses derived class as a super class
 Here A servers as base class for B which in turn serves as base
class for C.
 The chain ABC is known as inheritance path.
 This process may be extended to any number of levels.
 Write a program to store & display student information using
multilevel inheritance.
A
B
C
Grandparent class
Parent class
Child class

Hierarchical Inheritance
Account
CurrentFixed-DepositSavings
LongMediumShort
 Write a program to demonstrate use of hierarchical inheritance.

Method Overriding (IMP)
 In derived class we can create a method with same
signature as in base class.
 This concept is called as method overriding.
 This method can have same name, same arguments &
same return type as a method in base class.
 When the method is called, the method defined in the
subclass is invoked & executed.
 The method in base class should be specified as virtual.
 The method in base class should be specified with keyword
override.

Example
using System;
class Super
{
public int x;
public Super(int x)
{
this.x=x;
}
public virtual void Display()
{
Console.WriteLine("Super
x="+x);
}
}
class Sub:Super
{
int y;
public Sub(int x,int y) : base(x)
{
this.y=y;
}
public override void Display()
{
Console.WriteLine("Super
x="+x);
Console.WriteLine("Sub y="+y);
}
}
class Test
{
{
Sub s1=new Sub(100,200);
s1.Display();
}
}

Method Hiding (IMP)
 With the help of virtual & override
keywords we can hide an method
declared in a base class.
 What if the class is provided by
someone else?
 Here the base class method cannot be
declared as virtual.
 To override such method use modifier
new to tell the compiler the derived
class method “hides” the base class
method.
 Example:
using System;
class Base
{
public void Display()
{
Console.WriteLine("Base Method");
}
}
class Derived:Base
{
public new void Display()
{
Console.WriteLine("Derived
Method");
}
}
class HideTest
{
{
Derived d=new Derived();
d.Display();
}
}

Abstract Classes
 At times we can have one base
class & a number of different
derived classes.
 The top-most base class simply
acts as a base for others & is not
useful on its own.
 We might not want to create an
objects of such classes.
 This can be done by making the
class as abstract.
 Example:
abstract class Base
{
………
}
class Dervied:Base
{
……..
}
…….
…….
Base b1; //Error
Derived d1; //Ok
 Characteristic:
 It cannot be instantiated
directly.
 It can have abstract members.
 We cannot apply a sealed
modifier to it.

Abstract Methods
 Method declaration includes
the modifier abstract.
 It is implicitly a virtual
method & does not provide
any implementation.
 An abstract method does not
have a method body.
 Example:
public abstract void Draw (int
x, int y);
 Characteristics:
1. It cannot have
implementation.
2. Its implementation must be
provided in non-abstract
derived classes by overriding
the method.
3. It can be declared only in
abstract classes.
4. It cannot take either static
or virtual modifiers.
5. An abstract definition is
permitted to override a
virtual method.

Sealed Classes: Preventing Inheritance
 Prevent a class from being further sub classed.
 Such classes are called sealed classes.
 Example:
sealed class AClass
{
…..
}
sealed class BClass:Someclass
{
…..
}
 Any attempt to inherit these classes will cause an error & compiler will
not allow it.
 Standalone utility classes are created as sealed classes.

Sealed Methods
 When an instance method declaration includes the sealed modifier, the
method is said to be a sealed method.
 A derived class cannot override this method.
 A sealed method is used to override an inherited virtual method with the
same signature.
 Example:
class A
{
public virtual void Fun()
{
……
}
}
class B: A
{
public sealed override void Fun()
{
……
}
}
 Now any derived class of B cannot further override the method Fun().

Polymorphism
 Means ‘one name ….. many forms’.
 Polymorphism can be achieved in two ways:
Polymorphism
Inclusion
Polymorphism
Operation
Polymorphism
Using
Virtual
Methods
Using
Overloaded
Methods

Operation Polymorphism
 Implemented using overloaded methods & operators.
 Overloaded methods are selected for invoking by matching
arguments, in terms of number, type & order.
 This information is known to compiler at compile time.
 Also called as early binding, or static binding or static
linking.
 Also known as compile time polymorphism.
 Early binding means an object is bound to its method call
at compile time.

Example
using System;
class Dog
{
}
class Cat
{
}
class Operation
{
static void Call(Dog d)
{
Console.WriteLine("Dog is
called");
}
static void Call(Cat c)
{
Console.WriteLine("Cat is
called");
}
{
Dog dog=new Dog();
Cat cat=new Cat();
Call(dog);
Call(cat);
}
}

Inclusion Polymorphism
 Achieved through use of virtual functions.
 Assume class A implements virtual method M. Classes B &
C are derived from A and override method M. When B is
cast to A, a call to method M from A is dispatched to B.
Similarly when C is cast to A, a call to method M from A is
dispatched to C.
 Also known as run-time polymorphism.
 Since method is linked with a particular class much later
after compilation, this process is also called late binding.
 Also known as dynamic binding as the selection of method
is done dynamically at run time.

Example
using System;
class Maruti
{
public virtual void Display()
{
Console.WriteLine("Maruti Car");
}
}
class SX4:Maruti
{
{
Console.WriteLine("SX4 Car")
}
}
class Swift:Maruti
{
{
Console.WriteLine("Swift Car");
}
}
class Inclusion
{
{
Maruti m=new Maruti();
m=new SX4();
m.Display();
m=new Swift();
m.Display();
}
}

Chapter : 14
Interfaces: Multiple Inheritance

Introduction
 C# does not support multiple inheritance.
 A class cannot have more than one superclass.
 C# provides an approach known as interface to
support the concept of multiple inheritance.
 An interface is a class with some differences:
 All members of an interface are implicitly public &
abstract.
 An interface cannot contain constant fields,
constructors & destructors.
 Its members cannot be declared static

Defining an Interface
 General Form:
interface Interfacename
{
member declarations;
}
 Like classes, interfaces can also be extended.
 That is, an interface can be sub interfaced from other interfaces.
 General Form:
interface name2:name1
{
Members of name2
}
 Note: An interface can not extend classes

Example: 1
using System;
interface Addition
{
int Add();
}
interface Multiplication
{
int Mul();
}
class Computation:Addition,Multiplication
{
int x,y;
public Computation(int x,int y)
{
this.x=x;
this.y=y;
}
public int Add()
{
return(x+y);
}
public int Mul()
{
return(x*y);
}
}
class InterfaceTest
{
{
Computation com=new Computation(10,20);
Addition add=(Addition)com; //casting
Console.WriteLine("Sum="+add.Add());
Multiplication mul=(Multiplication)com;
Console.WriteLine("Product="+mul.Mul());
}
}

Example: 2 --- Multiple Implementation of an Interface
using System;
interface Area
{
double Compute(double x);
}
class Square:Area
{
public double Compute(double x)
{
return(x*x);
}
}
class Circle:Area
{
public double Compute(double x)
{
return(Math.PI*x*x);
}
}
class Interface2
{
{
Square s=new Square();
Circle c=new Circle();
Area area;
area=s as Area;
Console.WriteLine("Area of
Square="+area.Compute(10.2));
area=c as Area;
Console.WriteLine("Area of
Square="+area.Compute(10.2));
}
}

Interfaces & Inheritance
 A base class of a derived class may
implement an interface.
 When an object of the derived class is
converted to the interface type, the
inheritance hierarchy is searched for a
class that directly implements the
interface.
 Example:
using System;
interface Display
{
void Print();
}
class B:Display
{
public void Print()
{
Console.WriteLine("Base
Display");
}
}
class D:B
{
public new void Print()
{
Console.WriteLine("Derived
Display");
}
}
class Interface3
{
{
D d=new D();
d.Print();
Display dis=(Display)d;
dis.Print();
}
}

Explicit Interface Implementation
 It may be possible that multiple
interface have a method of a same
name.
 This may create a problem when a
class implements more than one
interface.
 C# supports a technique known as
explicit interface implementation,
which allows a method to specify
explicitly the name of the interface it
is implementing.
 Example:
using System;
interface I1
{
void display();
}
interface I2
{
void display();
}
class C1:I1,I2
{
void I1.display()
{
Console.WriteLine("I1 Display");
}
void I2.display()
{
Console.WriteLine("I2 Display");
}
}
class Interface4
{
{
C1 c=new C1();
I1 i1=(I1)c;
i1.display();
I2 i2=(I2)c;
i2.display();
}
}

Abstract Class & Interfaces
 An abstract class can use an interface in the base class list.
 Here the interface methods are implemented as abstract methods.
 Example:
interface A
{
void Method();
}
abstract class B:A
{
……….
……….
public abstract void Method();
}
 Here class B does not implement the interface method; it simply redeclares as a
public abstract method.
 It is the duty of the class that derives from B to override & implement the method.

Chapter : 15
Operator Overloading

Introduction
 The C# operators can be defined to work with the user-defined data
types such as structs & classes.
 C# has the ability to provide the operators with a special meaning
for a data type.
 This mechanism of giving such special meaning to an operator is
known as operator overloading.
 Following is list of operators that can be overloaded.
Category Operators
1. Binary Arithmetic +,*,/,-,%
2. Unary Arithmetic +,-,++,--
3. Binary bitwise &,|,^,<<,>>
4. Unary bitwise !,~,true,false
5. Relational Operators ==,!=,>=,<,<=,>

Cont…
 Following is list of operators that cannot be overloaded.
Category Operators
1. Conditional operators &&,||
2. Compound assignment +=,-=,*=,/=,%=
3. Other operators [ ],( ),=,?:,->,new,sizeof,typeof,is,as

Need for Operator Overloading
 Operator overloading gives us syntactical convenience.
 It helps us to generate more readable code in a number of
situations. These includes:
 Financial programs.
 Mathematical or physical modeling
 Graphical programs
 Text manipulations
 General form of an operator method:
public static retval operator op(arglist)
{
Method body…..
}

Overloading Unary Operators
using System;
class Space
{
int x,y,z;
public Space(int a,int b, int c)
{
x=a;
y=b;
z=c;
}
public void Display()
{
Console.Write(" "+x);
Console.Write(" "+y);
Console.Write(" "+z);
}
public static Space operator -(Space s)
{
s.x=-s.x;
s.y=-s.y;
s.z=-s.z;
return(s);
}
}
class SpaceTest
{
{
Space s=new Space(10,-
20,30);
Space q;
Console.Write("S: ");
s.Display();
q=-s;
Console.Write("Q: ");
q.Display();
}
}

Overloading Binary Operators
using System;
class Complex
{
double x,y;
public Complex(){ }
public Complex(double real,double
imag)
{
x=real;
y=imag;
}
public static Complex operator +
(Complex c1,Complex c2)
{
Complex c3=new Complex();
c3.x=c1.x+c2.x;
c3.y=c1.y+c2.y;
return(c3);
}
public void display()
{
Console.Write(x);
Console.Write(" + j"+y);
}
}
class ComplexTest
{
{
Complex a,b,c;
a=new Complex(2.5,3.5);
b=new Complex(1.6,2.7);
c=a+b;
c.display();
}
}

Overloading Comparison Operators
 C# supports six comparison operators that can be
considered in three pairs:
 == & !=
 > & <=
 < & >=
 The significance of pairing is two-fold:
 Within each pair, the second operator should always
give exactly the opposite result to the first.
 C# always requires us to overload the comparison
operators in pairs. That is, if we overload ==, then we
must overload != also, otherwise it is an error.

Example:
using System;
class Vector
{
int x,y,z;
public Vector(int a,int b,int c)
{
x=a;
y=b;
z=c;
}
public static bool operator ==(Vector
v1,Vector v2)
{
if(v1.x==v2.x && v1.y==v2.y)
return(true);
else
return(false);
}
public static bool operator !=(Vector
v1,Vector v2)
{
return(!(v1==v2));
}
}
class CompareTest
{
{
Vector u1=new Vector(1,2,3);
Vector u2=new Vector(1,2,3);
if(u1==u2)
Console.WriteLine("U1 is equal to
U2");
else
Console.WriteLine("U1 is not equal to
U2");
}
}

Chapter : 16
Delegates & Events
(IMP)

Introduction
 A delegate object is a special type of object that contains
the details of a method rather than data.
 Delegates in C# is used for two purposes:
 Callback
 Event Handling
 Dictionary meaning of delegate is “a person acting for
another person”, in C# it means a method acting for
another method.
 A delegate in C# is a class type object & is used to invoke a
method that has been encapsulated into it at the time of its
creation.

Delegate Declaration
 General Form:
 modifier delegate return-type delegate-name(parameters);
 Delegate is derived from System.Delegate class.
 The modifier controls the accessibility of the delegate.
 Delegate may take any of the following modifiers:
new, public, private, protected, internal.
 It is a class type & can be declared in any place where a
class definition is permitted.
 A delegate may be defined in the following places:
 Inside a class
 Outside all classes
 As the top level object in a namespace.

Delegate Methods
 The methods whose references are encapsulated
into a delegate instances are known as delegate
methods (or callable entities)
 The signature & return type of delegate methods
must exactly match the signature & return type
of the delegate.

Delegate Instantiation
 A delegate-creation-expression is used to create a new instance of
a delegate.
 General Form:
 new delegate-type(expression)
 Here the delegate-type is the name of the delegate declared
earlier whose object is to be created.
 Expression must be the method name.
 The method & the object to which a delegate refers are
determined when the delegate is instantiated.
 This remains constant for the entire lifetime of the delegate.
 It is not possible to change them, once the delegate is created.

Delegate Invocation
 When a delegate is invoked, it in turn invokes
the method whose reference has been
encapsulated into the delegate.
 General Form:
 delegate_object(parameter list);
 The optional parameter list provides values for the
parameters pf the method to be used.

Example:
using System;
//Delegate Declaration
delegate int ArithOp(int x,int y);
class MathOperation
{
public static int Add(int a,int b)
{
return(a+b);
}
public static int Sub(int a,int b)
{
return(a-b);
}
}
class DelegateTest
{
{
ArithOp op1=new
ArithOp(MathOperation.Add);
ArithOp op2=new
ArithOp(MathOperation.Sub);
int result1=op1(3,20);
int result2=op2(40,20);
Console.WriteLine("Result1="+result1
);
Console.WriteLine("Result2="+result2
);
}
}

Multicast Delegate
 It is possible for delegates to hold & invoke multiple
methods.
 Such delegates are called multicast delegates.
 Also known as combinable delegates.
 They must satisfy following conditions:
 Return type of such delegate must be void.
 None of the parameters of the delegates can be declared as
output parameters, using out keyword.
 If D is a delegate & d1,d2,d3 & d4 are its instances, then
the statements:
 d3=d1+d2 //refers to two methods.
 d4=d3-d2 //refers to only d1 method

Example
using System;
delegate void MDelegate();
class DM
{
public static void Display()
{
Console.WriteLine("In Display");
}
public static void Print()
{
Console.WriteLine("In Print");
}
}
class MDelegateTest
{
{
MDelegate m1=new
MDelegate(DM.Display);
MDelegate m2=new
MDelegate(DM.Print);
MDelegate m3=m1+m2;
MDelegate m4=m2+m1;
MDelegate m5=m3-m2;
m3();
m4();;
m5();
}
}

Events(IMP)
 An event is a delegate type class member that is used by
the object or class to provide a notification to other object
that an event has occurred.
 The client object can act on an event by adding an event
handler to the event.
 General Form:
 modifier event type event-name;
 Since events are based on delegates, we must first declare
a delegate and then declare an instance of the delegate
using the keyword event.

Example
using System;
//Delegate Declaration
delegate void EDelegate(string str);
class EventClass
{
public event EDelegate Status;
public void TriggerEvent()
{
Status("Event Triggered");
}
}
class EventTest
{
{
EventClass ec=new
EventClass();
EventTest et=new
EventTest();
ec.Status+= new
EDelegate(et.EventCatch);
ec.TriggerEvent();
}
public void EventCatch(string
str)
{
Console.WriteLine(str);
}
}

Chapter : 17
Managing Console I/O Operations

The Console Class
 The methods for reading & writing to the console are
provided by the System.Console class.
 This class gives us access to the standard input, standard
output & standard error streams:
Stream Object Represents
Console.In Standard Input
Console.Out Standard Output
Console.Error Standard Error

Console Input
 Supports two methods for obtaining input from
the keyboard.
 Read(): Returns a single character as int.
 ReadLine(): Returns a string containing a line of text.

Console Output
 Supports two methods for writing to the console.
 Write(): Outputs one or more values to the screen
without a new line character.
 WriteLine(): Outputs one or more values to the
screen but adds a new line character at the end of the
output.

Exercise
 Write a program in C# to print the following
output:
1
2 2
3 3 3
4 4 4 4
5 5 5 5 5
6 6 6 6 6 6
7 7 7 7 7 7 7
8 8 8 8 8 8 8 8
9 9 9 9 9 9 9 9 9

Formatted Output
 Use overloaded WriteLine()
method.
 General Form:
 Console.WriteLine(format-
string, v1, v2, ….);
 Format String contains both
static text & markers which
indicate
 Where the values are to be printed.
 How the values are to be formatted.
 Example
 Console.WriteLine(“Sum of {0}
and {1} is {2}”,a,b,c);
 We can also specify a width for
the value using the format:
 { n , w }
 n is the index number
 w is the width for the value
 Example:
int a=45;
int b=976;
int c=a+b;
Console.WriteLine(“{0,5n+{1,5}
n} ------- n{2,5}”,a,b,c);
4 5
+ 9 7 6
-----------
1 0 2 1

Chapter : 18
Managing Errors & Exceptions

Programming in c#

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