Sudhir c Sharp Book

8/12/2019 Sudhir c Sharp Book

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Copyrights Chekuri group

Contents:

Chapter 1

Introduction to C#.NET

Rules in C#.NET

Datatypes

Operators

Creating first console application

Basic C#.NET program structure in Console Application

Console Methods

Write

WriteLine

Read

ReadLine

Chapter 2

Variables

Predefined Methods

Implicit Conversion

Explicit Conversion

Boxing

UnBoxing

Chapter 3

Arrays

Single dimension arrays

Multidimensional arrays

Jagged Array

Chapter 4Conditional statements

Branching

Looping

If

If Else


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Else if

Nested if

Switch

Chapter 5

for

for each

while

do while

Chapter 6

OOPS

methods

General methods

Methods with arguments

Methods with return typeMethods with arguments and return type

Static method

Class

Object

Chapter 7

Encapsulation

Inheritance

Single inheritance

Multi level inheritance

Hierachical inheritance

Multiple inheritance

Hybrid inheritance

Sealed class

Chapter 8

Abstraction

Access specifiers


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Private

Public

ProtectedInternal

Protected Internal

Creating userdefined namespace or dll

Chapter 9

Polymorphism

Method overloading

Method overriding

Abstract method

Abstract class

Partial class

Chapter 10

Interface

Inheriting Multiple interfaces

Delegates

Single delegates

Multcast delegates

Exception handling

Try

Catch

Finally

Throw


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Chapter 1

Introduction to C#.NET

C#.NET is an object oriented programming language and it isa part of .NET.

It is used as a code behind language in DOTNET applications. It is the most popular language in .NET because it has the

same syntax of programming languages like C, C++, JAVA.

It is written as C# but pronounced as C Sharp because # is nottaken from maths it is a musical note which is pronounced asSharp.

It is a case sensitive language i.e., Lowercase letter is not sameas Uppercase letter.

Example

int i; and int I; they are different variables.

Every block of code starts with opening curly brace and endwith closing curly brace.

opening brace {

} closing brace

All the keywords in C# will be in lowercase.Example

int, using, class, ...

Predefined namespaces, classes and methods will start withuppercase letter(Every word starts with uppercase letter).

ExampleSystem, Console, Read

Namespace is a collection of classes. Class is a collection of methods and its members.

Rules in C#.NET


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Every C# statement should end with semicolon (;).Example

Console.Write("hello world"); Every string value should be surrounded by double quotes.

Example

string s="hai";

Every character value should be surrounded by single quotes.Example

char c='a';

No need of any quotes around numeric values.Example

int i=515; float f=533.558f;

Every line of code in C# should be in class. // is for comments in C#

Datatypes

Datatypes and memory in bytes

Byte 1

Short 2

Int 4

Long 8

Sbyte 1

Ushort 2

Uint 4

Ulong 4

Float 4

Double 8

Decimal 16

Bool 1

Char 2

String 20+

Object 8+


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Example program with all datatypesusingSystem;

usingSystem.Collections.Generic;

usingSystem.Linq;

usingSystem.Text;

namespacedatatypes

{ classProgram

{//main function is the starting point

staticvoidMain(string[] args)

{

inti = 10;

intj = 20;

//int i = 234.234;

//the text in double quotes will print as it is and value in ivariable is printed next to that.

Console.WriteLine("int: "+i);//int: 10

Console.WriteLine("sum: "+(i+j));//sum: 30

floatf = 23.23f;floatf1 = 245;

Console.WriteLine("float: "+(f+f1));//float: 268.23

charc = 'a';

// char c='abad';

// char c = a;

Console.WriteLine("char: "+c);//char: a

strings = "abc";

// string s = abc;


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//string s='abd';

strings1 = "def";

Console.WriteLine(s+s1);//abcdef

Console.WriteLine("string: "+s+s1);//string: abcdef

//+ is used as concatenation(side by side) for strings

//+ is used as addition operator for numeric datatypes

Console.WriteLine(s+"\n"+s1);

// \n is used to go to new line it should be in double quotes

boolb = true;

boolb1 = false;

//bool b2 = "abc";

Console.WriteLine(b);//true

Console.WriteLine(b1);//false

objecto = 123;

objecto1 = 'a';

objecto2 = "abc";

objecto3 = 234.234f;

objecto4 = true;

Console.WriteLine("object: "+o3);

Console.ReadKey();

}}

}


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Operators

Arithmetic operators:

Used to work with numeric data types.

eg: int , float, double, long, decimal, short...

+ (addition) eg: a+b

- (substraction) eg: a-b

* (multiplication) eg: a* b

/ (division) eg: a/b

% (modulus) eg: a%b

= equal to

Assignment operators;

+=

eg: a+=b; ie., a=a+b;

-=

eg: a-=b; ie., a=a-b;

*=

eg: a*=b; ie., a=a*b;/=

eg: a/=b; ie., a=a/b;

%=

eg: a%=b; ie., a=a%b;


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Unary operator;

++ (increment)-- (decrement)

i++(post increment)

1 is added to i after the code is executed.

++i (pre increment)

1 is added to i before the code gets executed.

i--(post decrement)

i is decreased by 1 after the code is executed.

--i(pre decrement)

i is decreased by 1 before the code gets executed.

Example programusingSystem;

usingSystem.Collections.Generic;

usingSystem.Linq;

usingSystem.Text;

namespaceConsoleApplication1

{

classProgram

{

staticvoidMain(string[] args)

{

inti = 1;

intj = i++;

Console.WriteLine(j);//1

Console.WriteLine(i);//2Console.WriteLine("----------------------");

intx = 1;

inty = ++x;

Console.WriteLine(y);//2


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Console.WriteLine(x);//2

Console.ReadKey();

}}

}

Relational operators:

Used to compare two values in variables.

Used in conditional statements.

> greater than

< less than

>= greater than or equal to


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eg: a=3>>4 ie., 3/2^4 =146

Operator precedence:

Based on the operator priority arthmetic statements are solved.

bodmas

brackets, division, multiplication, addition, substraction.

Creating first console application

Open visual studio. Click on file in menu. New project. Select a language as c# from the left side. Select console application from the list of applications. Give the name to the project Select the location to save the project. click on ok. Now default environment to create console application is

displayed.

F5 is the shortcut key to start debugging or to execute aprogram (or) click on play symbol button present in the center

of top menu of visual studio tool.

Shift + F5 for stop debugging or execution.

Basic C#.NET program structure in Console Application

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace first

{

class Program

{


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static void Main(string[] args)

{

}}

}

Explanation:

using- using is a keyword used to import a namespace to use the

classes inside it in your coding.

System- System is a namespace name which consists of classes used

in coding.

Like System we also have many namespaces given by Microsoft.

By default we get the above four namespaces.

first- first is the project name what you have given while creating this

console application.

Program- Program is the default class name for every console

application.Main- Main is the method is acts as the starting point for every

application.

There should be only one main function for every project.

Main is a static method which is created using static keyword and as it

is a static method memory for main is created in ram when program is

executed.

void- void is the return type of Main method.

Method with void return type returns nothing so main method also

returns nothing.

string[] args- Main method will take input arguments in the form of

string array.

We can also remove the namespaces like System.Text which are not

used in the program.

Console Methods

Console is a class under System namespace.

Under Console class we have 5 important methods.

1. ReadKey

2. Write


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3. WriteLine

4. Read

5. ReadLine

These five methods plays a prominent role in developing console

applications.

If System namespace is not added at the top of the program we have

to use it everywhere where Console class is used.

Example:

Console.Write("System is added");

System.Console.Write("System is not added");

ReadKey

ReadKey method is under Console class used to stop theoutput screen of a console application from closingimmediately after program execution till we press a key.

So use Console.ReadKey( ) line at the end of Main function inevery program to see the output.

It doesn't take any parameter between the braces.

Example program to print a simple message using ReadKey:

using System;

namespace readkey

{

class Program

{


{Console.ReadKey();

}

}

}


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Output:

_

Explanation:

Blank blank ouput screen waits without closing till you press a key this

is because of ReadKey method.

If that line is removed the output screen will close immediately after

program execution completed.

Write

Write method is under Console class. It is used to print a message on the output screen of console

application.

When you print a message using Write the cursor will appearnext to the message.

It prints the text as it is present in the double quotes. It also prints the value present in variable.

Example program to print a simple message using Write:

using System;

namespace write

{

class Program

{


{

Console.Write("Hai this is Write example");Console.ReadKey();

}

}

}


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Output:

Hai this is Write example_

Explanation:

In the above program Write is a method under Console class used to

print a message on the output screen with a cursor blinking next to

message.

As Console class is under System namespace we have to add it at the

top.

ReadKey method is used to make output screen without closing

immediately.

We can also write the above program without adding System

namespace as below.

Example program to print a simple message on using Write

without adding System namespace:

namespace write

{

class Program

{


{

System.Console.Write("Hai this is Write example");

System.Console.ReadKey();

}

}

}

Output:

Hai this is Write example_

Explanation:


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Read

Read method is under Console class used to Read data fromthe user given in runtime.

When you read a message using Read the cursor willappear in the same line.

Return type of Read method is int ie., it returns back the datagiven by the user in the form of int.

It returns ascii value of the given data. It doesn't take any parameter between the braces.

Example:

int i=Console.Read();Console.Write(i);

if the user enters a its ascii value 97 is stored in i.

Here, Console.Write method is used to print the value inside i, So, the

output will be 97.

Example program to print a simple message using Read:

using System;

namespace read

{

class Program

{


{

int i=Console.Read();Console.Write("\n");

Console.Write("you entered: "+i);

Console.ReadKey();

}

}


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}

Output:

a

you entered: 97_

Explanation:

In the above program i is a variable of int datatype which is used to

store the ascii value of the data given by user in runtime using Read

method. First Write method is used for new line and second Write

method is used to print message "you entered: " as it is and also to

concatenate the value present in the variable i as show in the output.

ReadLine

ReadLine method is under Console class used to Read datafrom the user given in runtime.

When you read a message using ReadLine the cursor willappear in the next line.

Return type of ReadLine method is string ie., it returns backthe data given by the user in the form of string.

It returns the value as it is given by the user so ReadLinemethod is preferred to take input data from the user in

runtime.

It doesn't take any parameter between the braces.

Example:

string s=Console.ReadLine();Console.Write(s);

if the user enters a then a as it is stored in string variable s.

Here, Console.Write method is used to print the value inside s, So, the

output will be a.


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Example program to print a simple message using ReadLine:

using System;namespace readline

{

class Program

{


{

string s=Console.ReadLine();

Console.Write("you entered: "+s);

Console.ReadKey();

}

}

}

Output:

a

you entered: a_

Explanation:

In the above program s is a variable of string datatype which is used

to store the value given by user in runtime using ReadLine method.

Write method is used to print message "you entered: " as it is and

also to concatenate the value present in the variable s as show in the

output.

Chapter 2

Variables

Variable is used to store a value of a specific datatype. Memory for a variable is allocated in stack memory. The value is a variables keeps on changing throughout the

program.


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Example:

int i;

i=10;Here i is a variable of type int.

So, the value between -2,147,483,648 to 2,147,483,648 can be stored

in variable i.

In the second statement value 10 is stored in i.

We can also intialize the variable with some value when it is created

like below.

Example program to create a variable of int type, initialization

and also assigning value to it:

using System;

namespace variable

{

class Program

{static void Main(string[] args)

{

int i=10;

i = 20;

Console.Write(i);

Console.ReadKey();

}

}

}

Output:

20_

Explanation:

In the above program i is a variable of int datatype. It is intialized witha value of 10. In the next statement i is assigned with a new value 20.

So, the value in the variable is changed from 10 to 20. When we print

the value in variable i using WriteLine the output is 20.


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In the same way we can create any number of variables in a program

with specific datatypes and based on the datatypes values should be

stored in variables.

Example program for creating variables with different datatypes

and printing values in them:

using System;

namespace variable

{

class Program

{


{

int i = 20; float f = 23.234f; char c = 'b'; string s = "def"; bool b

= false;

Console.WriteLine(i+f);

Console.WriteLine(c+s);Console.WriteLine(i+c);

Console.WriteLine(i+s);

Console.WriteLine(b);

Console.ReadKey();

}

}

}

Output:

43.234

bdef

118

20def

false

_

Explanation:

There are 4 variables i, f, c, s, b with datatypes int, float, char, string,

bool respecitively.


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int and float is of numeric datatypes so variables i and f stores

numbers and there is no need of having quotes around the values.

f is of float type so it can store numeric value with decimal point butwhen f should be the suffix for the value which is assigned to f.

c variable is of char type and it is capable of storing only one character

at a time whereas variable s can store multiple characters as it is of

string datatype.

b variable is capable of storing either true or false value only.

i + f = 20 + 23.234 = 43.234

As i and f are numeric types + is used as addition arthimetic operator

and they are added.

c + s= b + def = bdef

As c is char and s is string + is used as concatenation operator and

they are concatenated.

i + c = 20 + b = 20 + 98 = 118

As i is integer and c is char the ascii value of c is added to i ie., ascii of

b is 98 added to 20 gives output as 118.

i + s = 20 + def = 20defAs s is string it cannot be converted into ascii value so here + is used

for concatenating values of i and s.

b = false

Value inside b is false and it is printed as it is.

Predefined methods

Predefined methods are the inbuilt methods we have in C#.NET which

do something or returns a value.

We have predefined methods like

minvalue( ):

min value is a method used to find out the minimum value a numeric

datatype can store.

It is only for numeric types.

maxvalue( ):

max value is a method used to find out the maximum value a numeric

datatype can store.


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It is only for numeric types.

Example program to print minvalue and maxvalue of numericdatatypes int, uint, long, float, double, decimal

using System;


using System.Linq;

using System.Text;

namespace min_max_value

{

class Program

{


{

Console.WriteLine(int.MinValue);

Console.WriteLine(int.MaxValue);Console.WriteLine(uint.MinValue);

Console.WriteLine(uint.MaxValue);

Console.WriteLine(long.MinValue);

Console.WriteLine(long.MaxValue);

Console.WriteLine(float.MinValue);

Console.WriteLine(float.MaxValue);

Console.WriteLine(double.MinValue);

Console.WriteLine(double.MaxValue);

Console.WriteLine(decimal.MinValue);

Console.WriteLine(decimal.MaxValue);

Console.ReadKey();

}

}

}

output:


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Example program to print even numbers between 10 and 45 using

for loop and if condition:

using System;

namespace variable

{

class Program

{


{

for (int i = 10; i < 45; i++)

{

if (i % 2 == 0)

{ Console.WriteLine(i); }

}

Console.ReadKey();}

}

}

Output:

10

12

14

16

18

20

22

24

26

2830

32

34

36

38


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40

42

44

Implicit Conversion

Converting small data type values to large data type values

automatically by the compileris known as "Implicit Conversion".

Example:

int i=10;

long l=i;

Console.Write(l);//10

Explanation:

int data type is smaller than long data type ie., int data type occupies

small range as compare to long data type.so conversion of int to longis possible.it is an example of implicit conversion.

Explicit conversion

Converting large data type values to small data type values explicitly

by the developer is known as "Explicit Conversion".

Example:

long l=10;

int i=Convert.ToInt32(l);

Console.Write(i);//10

Explanation:

long data type is longer than int data type ie.,long occupies long

range as compare to int.so conversion of long to int is difficult to thedeveloper.so developer use the method Convert.ToInt32() to convert

long values into int values.Then conversion is possible and easy.

Boxing


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Converting value type to reference type is known as "Boxing".

Example:

int i=10;object o=i;

Console.WriteLine(o);//10

Explanation:

In the above example int datatype is value type.object is reference

type.so conversion of int to object is possible and it is an example

of boxing.

UnBoxing

Converting reference type to value type type is known as "UnBoxing".

Example:

object o=10;

int i=Convert.ToInt32(o);

Console.WriteLine(i);//10

Explanation:

In the above example object is reference type.int is value

type.conversion of object to int is not possible.so here we use

Convert.ToInt32() to convert object to int.

Chapter 3

Arrays

Array is a type used to store multiple values of same data typeunder a single name.

Arrays allows to store multiple values but all the values shouldbe same data type.

The elements can't exceed the number while creating an array. Arrays are zero indexed that means index starts with zero.


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Arrays are objects in c#.Memory objects are created in heapmemory.

Index of an array will be used to retrieve values. Array.Reverse()is used to reverse the elements of an array. Array.Sort() is used to print values in ascending order. Array.Length() is used to get the no.of elements in the array.

Single Dimensional Array

Single Dimensional Array is used to store multiple values in a linear

fashion.

Syntax for creating a single dimensional array:

datatype[ ] arrayname=new datatype[no. of elements];

Example:

int[ ] i=new int[3];

Example program for creating single dimensional array using for

loop:

using System;using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace sdarray

{

class Program


{

//int[] i = new int[3];

// i[0] = 1;------Assign a value



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int[] i = new int[3] { 1, 2, 3 };

for (int a = 0; a < 3; a++)

{

Console.WriteLine(i[a]);

}

Console.ReadKey();

}

}

}

Output:

1

2

3

Example program for creating single dimensional array using

foreach loop:

using System;


using System.Linq;

using System.Text;

namespace sdarray

{

class Program

{


{

int[] i = new int[3] { 3,4,5 };foreach (int a in i)

{

Console.WriteLine(a);

}

Console.ReadKey();


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}

}

}

Output:

3

4

5

Multi Dimensional Array

Multi Dimensional Array is used to store elements in the form of a

table.

Syntax for creating a multi dimensional array:

datatype[ , ] arrayname=new datatype[row,col];

Example:

int[ ,] a=new int[2,3];

Example program for creating multi dimensional array using for

loop:

using System;


using System.Linq;

using System.Text;

namespace sdarray

{class Program

{


{

int[ , ] a = new int[2,3]{{5,6,3}, { 3,4,5} };


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{

class Program


{

int[][] a = new int[2][];

a[0] = new int[3] { 3, 4, 5 };

a[1] = new int[4] { 1, 2, 3, 4 };

for (int i = 0; i < 2; i++)

{

for (int j = 0; j < a[i].Length; j++)

{

Console.Write(a[i][j]);

}

Console.WriteLine("");

}

Console.ReadKey();}

}

}

Output:

345

1234

Chapter4

Conditional Statements

A block of code that executes basing upon a condition is "ConditionalStatement".Conditional statements are used to execute a block of

code only when the condition is satisfied.

Conditional statements are classified into two types.

1)Conditional Branching

2)Conditional Looping


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Conditional Branching

These statements allows you to branch code depending on whether

the certain conditions met or not.

C# has two constructs for branching code.

1)If Statement

2)Switch Statement

Conditional Looping

C# provides four different loops that allows you to execute a block of

code repeatedly until a certain condition is met.

Those are:

1) for loop

2) while loop3) dowhile loop

4) foreach loop

If Statement:

The if statement which allows you to test whether a specific conditionis met.

Syntax of If Condition:

if(condition)

{

//statements

}

Example program using if condition

using System;


using System.Linq;


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using System.Text;

namespace branching{

class Program

{


{

int i;

Console.WriteLine("Enter number");

i = Convert.ToInt32(Console.ReadLine());

if (i > 0)

{

Console.WriteLine("Positive");

}

Console.ReadKey();

}

}}

Output:

Enter number

12

Positive

Output-2:

Enter number

-5

_

Explanation:

In the above output we can give input is -5.here -5 is less than zero.so

nothing will be printed in output. Blank will be printed in output.

If else statement:


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It is one of the statement in conditional branching. It is used to check

whether the condition is true or false. if it is true, it goes to if condition

and print output. if it is false, it goes to else part of the program andprint the output.

Syntax for if else statement:

if(condition)

{

statement

}

else

{

statement

}

Example program using if else statement


using System.Linq;

using System.Text;

namespace ifelse

{

class Program

{


{

int i;



if (i > 0)

{Console.WriteLine("Positive");

}

else

{

Console.WriteLine("Negative");


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}

Console.ReadKey();

}}

}

Output:

Enter number

12

Positive

Output-1:

Enter number

-6

Negative

Explanation:

In the above example we can give input is 12 then the output will beprinted as positive because 12 is greaterthan zero.we can give input is

-6 then the output will be printed as negative because -6 is less than

zero.

Else if statement

This is one type of conditional branching.In this type the compiler 1st

goes to if condition,if it is false it goes to else if condition,it also false

finally goes to else statement and print output.

Syntax for Else if statement:

if(condition)

{statements

}

else if(condition)

{

statements


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}

else

{statements

}

Example program using Else if statement

using System;


using System.Linq;

using System.Text;

namespace ifelse

{

class Program

{

static void Main(string[] args){

int i;



if (i > 0)

{

Console.WriteLine("Positive");

}

else if(i


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Output:

Enter number223

Positive

Output-1:

Enter number

-741

Negative

Output-2:

Enter number

0

zero

Explanation:

In the above example we give input is 223,it is greater than zero,thenthe output will be printed as positive and we give input is -741 it is

less than zero,then the compiler goes to else if part of the program

and print output as negative and finally gives 0 it is equal to zero,then

the compiler goes to else pert of the program and print output as

zero.

Nested If Statement

It is one type of If statement.Nested If means if in if ie.,The if

statement contains another if within that.

Syntax for Nested If:

if(condition)

{if(condition)

{

if(condition)

{

statements


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}

}

}

Example program for Nested If Statements

using System;


using System.Linq;

using System.Text;

namespace ifelse

{

class Program

{


{

int i;

Console.WriteLine("Enter number");i = Convert.ToInt32(Console.ReadLine());

if (i > 0)

{

if (i > 5 && i < 10)

{

Console.WriteLine("Between 5 and 10");

}

}

Console.ReadKey();

}

}

}

Output:

Enter number

4_

Output-1:

Enter number

8


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12

Invalid

Explanation:

In the above example we can give input is 1 it prints output as One,

input is 2 print output as Two, if we can give input is any number

except 1 and 2 the output prints Invalid because if we can give input is

1 compiler executes case1 and we give i/p is 2 executes case2 then

print output as One and Two.we give any other number except 1 and

2 default case will execute and prints Invalid.

Another Example program for switch statement:

using System;


using System.Linq;

using System.Text;

namespace branching

{

class Program

{


{

int i = 4;

switch (i)

{

case 1:

case 2:

case 3:

Console.WriteLine("One");

break;

case 4:case 5:

Console.WriteLine("Two");

goto case 1;

default:

Console.WriteLine("Invalid");


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break;

}

Console.ReadKey();}

}

}

Output:

Two

One

Explanation:

In the above example we can assign i value as 4. So directly case 4 is

executed and print output is Two, next no break statement is available.

instead of break we write goto statement as goto case1,then after the

execution go and starts from case1 then the output one will be

printed. Finally the output will be Two and One printed line by line.

Chapter5

1)for loop:

for loop is used to execute a block of code repeatedly until the

condition is true. for loops are appropriate when you know exactly

how many times you want to perform the statements within the loop.Normally, forloop statements execute from the opening curly brace to

the closing curly brace without interruption. Every for loop can contain

three sections commonly.

Those sections are:

Initialization: Which sets the starting point of the loop.

condition: The code is executed until the condition satisfied ie.,until itreturns true value.

Iteration(Increment/Decrement): Once Condition has been

evaluated, the for loop gives to its control to third section ie.,

Iteration, which takes to the next side either positive or negative


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direction. Some times it will be incremented, sometimes decremented

depending on the situation.

Syntax for for loop:

for(initialize; condition; inc/dec)

{

statements

}

Example program using for loop

using System;


using System.Linq;

using System.Text;

namespace loops{

class Program

{


{

for (int i = 0; i < 4; i++)

{

for (int j = 0; j < i + 1; j++)

{

Console.Write("*");

}

Console.WriteLine("");

}

Console.ReadKey();

}}

}

Output:

*


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**

***

****

2)foreach loop

foreach loop is a special loop used for collections and arrays.It is

repeated based on the number of elements in a collection.It

automatically takes one by one element from a collection and it is

repeated till the last element is printed.

Syntax for foreach loop:

foreach(type variable in collect:ion/array)

{

statements

}

Example program using foreach loop

using System;


using System.Linq;

using System.Text;

namespace loops

{

class Program

{


{

int[] i = new int[3] { 7, 8, 9 };foreach (int a in i)

{

Console.WriteLine(a);

}

Console.ReadKey();


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}

}

}

Output:

7

8

9

3)While loop

whileloop will check a condition and then continues to execute a

block of code as long as the condition is true.

Syntax for While loop:

while(condition){

statements

}

Example program to print numbers from 0 to 5 using while loop

using System;


using System.Linq;

using System.Text;

namespace loops

{

class Program

{

static void Main(string[] args){

int i=0;

while (i


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i++;

}

Console.ReadKey();}

}

}

Output:

0

1

2

3

4

5

4)Dowhile loop

Dowhile loop is similar to the whileloop, except that it checks its

condition at the end of the loop. This means that the dowhileloop is

guaranteed to execute at least one time even the condition fails.

Syntax for dowhile loop:

do

{

statements

}

while(condition);

Example program to print numbers from 0 to 5 using dowhile

loop

using System;


using System.Linq;

using System.Text;


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namespace loops

{

class Program{


{

int i=0;

do

{

Console.WriteLine(i);

i++;

}

while(i


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Chapter6

OOPS

OOPS stands for Object Oriented Programming Structures.

It was a new approach in programming introduced in 1970's

Object Oriented approach provides us security and reusability of the

code.

To call a language as Object Oriented it needs to satisfy the below

oops concepts listed below

Encapsulation

Abstraction

Inheritance

Polymorphism

Before going to the discussion about oops concepts we have learn

what a method, object and a class is. They are the basic building

blocks in oops concepts.

Methods

Method is a named block of code or piece of code used toperform a particular task.

Methods may or may not return a value.

If it was a non value returning we use void as the return typefor a method.

If it was a value returning we use type of value as its returntype.

Syntax for creating a method:

Access_specifier return_type methodname( )

{//code

}

Access Specifier:It is used to define the accessibility level of a

method ie.,how long it is going to call.


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ex of access specifiers are public, private, protected etc.

ReturnType:What type of value a method is returning.

Method name: The name of a method to call it.

Example:

public void add( )

{ }

There are different types of methods

Simple Method

Method with arguments

Method with return type

Method with arguments and return type

Abstract Method

Static Method

Simple Method

Simple method is a method that doesn't have any arguments and

return type.

Syntax:

Access specifier void methodname( )

{ }

Example:

public void add()

{

Console.WriteLine("addition");}

The above method add will print addition as message on the ouput

screen. This is a simple method which taken no input and doesnt

return anything.


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Method with arguments

It is one type of method and consists of arguments/parameters.Arguments can be passed to a method which are inputs to the

method. The value passed to the method as arguments can be used in

the code of the method.

Example:

public void add(int a,int b)

{

Console.WriteLine(a+b);

}

Explanation:

In the above example the add( ) method can take two values of int

type as inputs and doesn't return any type because void is its returntype.

Method with Return Type

It is one of the method that doesn't have any arguments/parameters.

It contains only return type.

Example:

public int add()

{

int i=10;

int j=20;

return i+j;}

Explanation:

The above method add will return a value of int datatype.


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Method with arguments and return type

It is one of the method that contains both arguments and return type.

Example

public long add(int a,int b)

{

return a+b;

}

Explanation:

The above method add can take two parameters of int type and

returns a value of long datatype.

Abstract Method

Abstract method is a method which is created using

"abstract"keyword.

It doesn't have any implementation or body.

It will have only signature.

semicolon is required at the end of signature.It is implemented in the class which inherits it.

Syntax for creating abstract method:

abstract keyword access_specifier return_type method_name(input

parameters)

Example:

abstract public long add(int a,int b);

Explanation:


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The above method add is an abstract method which is created using

abstract keyword at the starting of the method signature. Signature

method means the whole line present there which defines a method.It accepts two parameters and returns a value of long datatype. It has

no body or implementation code.

Static Method

Static method is a method which can be called without any reference

or object because memory for a static method is created in RAM when

program is executed.

Static method is a method which is created using keyword "static".

Example:

Addition of two numbers using static method and takes input

arguments with return type


using System.Linq;

using System.Text;

namespace static_method

{

class Program

{

static void Main(string[ ] args)

{

long l = maths.add(4, 7);

Console.WriteLine(l);

Console.ReadKey();

}

class maths

{public static long add(int i, int j)

{

return i + j;

}

}


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}

}

Output:

11

Explanation:

add is a method created in maths class. The method add is called in

the main method directly using dot after class name as add is a static

class otherwise it has to be called using object of maths class.

class

Class is a blue print. It is a collection of methods and member functions. In C#.NET every line of code should be in class. Class can contain variable declarations as well as initialize

them at the time of declaration only.

Syntax:

class classname{

body

}

Example program using Class:

using System;


using System.Linq;using System.Text;

namespace static_method

{

class Program


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{


{maths m = new maths();

m.add();

Console.ReadKey();

}

class maths

{

public void add()

{

int a = 10;

int b = 20;

Console.WriteLine("Addition is:"+(a + b));

}

}

}

}

Output:

Addition is: 30

Object

Object is an instance of class. Object will have memory. To create this object "new" keyword is used.

It is a reference type.

Mandatory to use the "new" keyword for creating object.

Syntax:

classname objectname= new constructor;


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Example:

maths m=new maths( );

Explanation:

M is the name of the object created for maths class using new

keyword. Maths( ) is the constructor of the class maths.

Constructor will be explained later.

Example program using object for a class:

using System;


using System.Linq;

using System.Text;

namespace static_method{

class Program

{


{

maths m = new maths();

long l = m.add(3, 5);

Console.WriteLine("Sum is:"+l);

Console.ReadKey();

}

class maths

{

public long add(int i,int j)

{

return i + j;}

}

}

}


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Output:

sum is : 8

Chapter 7

Encapsulation

Encapsulation is a procedure of binding data under classname .

Encapsulation is a procedure of covering up of the data &functions into a single unit called as Class.

An encapsulated object is often called an abstract data type. Rather than defining the data in the form of public,we can

declare those fields as private. In other words wrapping up of data and methods into a single

unit is called as "Encapsulation"(ex:Class,method).

Inheritance

Acquiring or getting the properties from one class to anotherclass is known as "Inheritance".

In Object Oriented approach if we can apply parent/childrelation between classes.

Members of the parent class can be consumed by the childclasses.

Syntax:

class parent

{

body

}

class child : parent

{

body


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}

Example program:Two classes a & b with 2 methods display & show inside them with

inheritance

using System;


using System.Linq;

using System.Text;

namespace Inheritance

{

class Program

{


{

b o1 = new b();//creating object for the derived class

o1.show();//calling method from child classo1.display();//calling method from parent class

Console.ReadKey();

}

class a//parent or base class

{

public void display()

{

Console.WriteLine("display");

}

}

class b : a//child or derived class inherited with base class

{

public void show()

{

Console.WriteLine("show");}

}

}

}


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Output:

show

display

Single Inheritance

When a single derived class is derived from single baseclass,then that inheritance is called as "single inheritance".

In single inheritance we have single base class that is inheritedby the derived class.

Here the derived class has all the features of the base classand can add some new features.

The inheritance also depends on the access specifier that isused at the time of base class inheritance.

Syntax:

class Parent{

body

}

class child : parent

{

body

}

Example :

using System;


using System.Linq;

using System.Text;

namespace Inheritance{

class Program

{


{


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dad d = new dad();

d.car();

son s = new son();s.bike();

s.car();

Console.ReadKey();

}

class dad

{

public void car()

{

Console.WriteLine("car");

}

}

class son:dad

{

public void bike()

{Console.WriteLine("bike");

}

}

}

}

Output:

car

bike

car

Multi level Inheritance

Acquiring properties to a subchild class from the child classand also from the parent class.

When a derived class is created from another derivedclass,then that inheritance is called as "Multi level Inheritance".


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Syntax:

class parent{

body

}

class child1 : parent

{

body

}

class child2 : parent

{

body

}

Example:

using System;

using System.Collections.Generic;using System.Linq;

using System.Text;


{

class Program

{


{

grandfather g=new grandfather();

g.helicopter();

dad d = new dad();

d.helicopter();

d.car();

son s = new son();

s.helicopter();s.bike();

Console.ReadKey();

}

class grandfather

{


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public void helicopter()

{

Console.WriteLine("helicopter");}

}

class dad:grandfather

{

public void car()

{


}

}

class son : dad

{

public void bike()

{

Console.WriteLine("bike");

}}

}

}

Output:

helicopter

helicopter

car

helicopter

bike

Multiple Inheritance

One child with two parents is known as "Multiple Inheritance". Multiple Inheritance can contain only one derived class,two or

more base classes.

When a derived class is created from more than one baseclass then that inheritance is called as"Multiple Inheritance".


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Multiple Inheritance is not supported in c# .net because dueto ambiguity or confusion problem.

Syntax:

class Parent

{

body

}

class parent2

{

body

}

class child : parent,parent2

Example:

using System;


using System.Linq;using System.Text;


{

class Program

{


{

grandfather g = new grandfather();

g.helicopter();

dad d = new dad();

d.car();

Console.ReadKey();

}

class grandfather{


{

Console.WriteLine("helicopter");

}


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}

class dad

{public void car()

{


}

}

class son : dad, grandfather

{

public void bike()

{


}

}

}

}

Output:

An error will occur because a class cannot have multiple base classes

Hybrid Inheritance

Any combination of single, hierarchial and multi level inheritance is

called as "Hybrid Inheritance".

Syntax:

class base class

{

body

}

class derived class : base class{

body

}

class derived class1 : base class/derived class

{


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body

}

Example:

using System;


using System.Linq;

using System.Text;


{

class Program

{


{

grandfather g = new grandfather();

g.helicopter();

dad d = new dad();d.helicopter();

d.car();

son s = new son();

s.helicopter();

s.bike();

s.car();

Console.ReadKey();

}

class grandfather

{


{

Console.WriteLine("helicopter");

}

}class dad:grandfather

{

public void car()

{



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}

}

class son : dad{

public void bike()

{


}

}

}

}

Output:

helicopter

helicopter

car

helicopterbike

car

Sealed Class

A class which cannot be inherited by any other class is knownas "Sealed class".

It should be declared using "sealed" modifier. sealed classes are used to restrict the inheritance feature of

object oriented programming.

once a base class is defined as "sealedclass",this class cannotbe inherited.

In c#,the sealed modifier is used to define a class as "sealed". If a class is derived from a sealed class,compiler throws an

error.

Syntax:

sealed class classname

{


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body

}

class classname2:classname//Invalid because derived class will notinherit sealed class.

Example:

using System;


using System.Linq;

using System.Text;

namespace sealed

{

class Program

namespace sealed_class

{

class Program{


{

SealedClass sealedCls = new SealedClass();

int total = sealedCls.Add(4, 5);

Console.WriteLine("Total = " + total.ToString());

Console.ReadKey();

}

}

// Sealed class

sealed class SealedClass

{

public int Add(int x, int y)

{return x + y;

}

}

}


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Output:

Total = 9

Chapter 8

Abstraction

Hiding the complexity and providing the services is called"Abstraction".

In other words hiding the unnecessary data and providingrequired facilities is called "Abstraction".

ex: System.Console.ReadKey(); ReadKey() is used without writing lots of code in it. Another example is Tv remote.we can change the channels

but we don't know how the inner button works.

Access Specifiers

Access specifiers are also called as modifiers used to define scope of a

type as well as its members ie.,who can access it and who can't access

it.

C# supports five different access specifiers.Those are:

1)Private

2)Public

3)Protected4)Internal

5)Protected Internal

Private

Private can be used "Only with in the block". Members declared as private with in class or structure aren't

possible outside of them in which they are defined.

In C# the default scope for members of a class or structure is"Private".

Where as in case of interface default is "Public".Public


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A type or member of a type is declared as Public,that can be accessed

from "Anywhere".

Protected

Members declared as Protected under a class can be accessedonly from child classes.

Protected cannot consume non-child classes. Protected can be used "Only inherited class". Types under a namespace can't be declared as a Protected.

Internal

Internal can be used "Only with in the project". Members which are declared as internal were accessible only

with in the project both from child or non-child classes.

The default scope for a type in C# is "Internal"only.Protected Internal

Members declared as "Protected Internal" enjoy dual scopeie.,Internal and Protected.

With in the project they behave as "internal",providing accessto all other classes.

Outside the project they change to "Protected", and stillprovide access to child classes.Creating user defined dll or namespace

dll stands for "Dynamic Link Library".

It is an assembly.

It is a supportable file.

It is also known as "namespace",which is a collection of classes.

Namespaces are used in .exe files by adding them as references.

Namespaces are imported using the keyword "using".

Steps to create dll or namespace:


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Overloading".

2) Dynamic Polymorphism:

It is also known as "Run time polymorphism". It can have same

method name and same signature. It is also known as "Method

Overriding". Method Overriding can be used only when we have

inheritance.

Example:

using System;


using System.Linq;

using System.Text;

namespace polymorphism

{class Program

{

static void Main(string[ ] args)

{

y o = new y();

o.add(1, 3);

Console.ReadKey();

}

}

class x

{

public void add(int a, int b)

{

Console.WriteLine(a + b);

}}

class y : x

{

public void add(int a, int b)

{


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Console.WriteLine(a - b);

}

}

}

Output:

-2

Method Overloading

Method overloading is an approach which allows to definemultiple methods with the same name and different

signatures.

Method overloading can be done within a class as well asunder the child classes also.

Method overloading doesn't require any permissions tooverload a method from parent to child classes.

Method Overriding

Method overriding is an approach which allows to definemultiple methods with same name and same signatures.

Method overriding can be done only under child classes.

Method overloading requires an explicit permission tooverride a method from parent to child classes.

It can be done only we have inheritance.Abstract Method

Abstract method is a method which is created using "abstract"keyword.

Abstract method doesn't contain any implementation or body. In abstract method we have semicolon(;)at the end . Abstract method doesn't have curly braces. We can create abstract method only in abstract class.


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{

Program p = new Program();

p.add();p.sub();

Console.ReadKey();

}

//implementing abstract method in abstract class

public override void add()

{

Console.WriteLine("addition");

}

}

abstract class a

{

//abstract method

abstract public void add();

//genaral method

public void sub(){

Console.WriteLine("subtraction");

}

}

}

Output:

addition

subtraction

Partial Class

Partial class is a class which can be defined a single class inmultiple files,when compilation time these classes are

combined to form a single class. Partial classes can be defined with the keyword "partial". All the Partial classes must have the same accessibility. If any part is declared as "sealed",the entire class is sealed. If any part is declared as "abstract",the entire class is abstract.


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Method signatures must be unique for the types which aredefined partially.

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