C# with Renas

Nawroz University
Object Oriented
Programming
C-Sharp Programming
C# provides full support for object-oriented
programming including encapsulation,
inheritance, and polymorphism.
[2017/
2018]
Rekany
Renas Rajab Rekany
2017/2018

Renas Rajab Rekany OOP 2018
1
Object Oriented Programming
History of programming languages
1- Microsoft .Net Framework
.NET Framework (pronounced dot net) is a software framework developed by Microsoft that runs
primarily on Microsoft Windows. It includes a large class library known as Framework Class Library (FCL)
and provides language interoperability(each language can use code written in other languages) across
several programming languages. Programs written for .NET Framework execute in a software environment
(as contrasted to hardware environment), known as Common Language Runtime (CLR), an application
virtual machine that provides services such as security, memory management, and exception handling. FCL
and CLR together constitute .NET Framework.
FCL provides user interface, data access, database connectivity, cryptography, web
application development, numeric algorithms, and network communications. Programmers produce
software by combining their own source code with .NET Framework and other libraries. .NET
Framework is intended to be used by most new applications created for the Windows platform.
Microsoft also produces an integrated development environment largely for .NET software
called Visual Studio.
2-Different DOTNET Types of Applications
There are three main types of application that can be written in C#:
1. Winforms: Windows applications have the familiar graphical user interface of Windows
with controls such as buttons and list boxes for input.
2. Console: Console applications use standard command-line input and output for input and
output instead of a form.
3. Web Sites.

2
4- Create First Winforms application
Step 1: Start Visual Studio
Open the Microsoft Visual Studio 2008/2015.
Step 2: Create a new project
Go to File -> New Project, And then New Project Dialog Appears.
In the New Project Window, Select Visual C# as Project type and Windows Forms
Applications as the template. Give Name and Location to your project and finally
click OK button to create our first C# project.

4
Step 3: Design the user interface.
When the project is created, you will see the designer view of your interface as
follows.
Form Designer View
In this designer view of the form (Form1.cs [Design]), you can design the user
interface of the single form. To do that, we use the 'Toolbox' which contains the
items that you can add to your form. Toolbox is placed on the left side of your visual
studio. If it is not visible go to View -> Toolbox to show the Toolbox.
Toolbox

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It contains Labels, Buttons, Check Boxes, Combo Boxes and etc. This can be used to
design your interface. To add elements from the Toolbox to your form double click
the item or drag the item to your form.
Now add a Button Control to your form by simple dragging a Button control into the
form designer view. Finally it looks like below.
Now our form contains two elements. Those are form and the button control. These
elements have properties such as name, text, background color, fore color, etc.... To
see properties for a control, select the control and all the properties are displayed in
the Properties Window which appears on the right side of your visual studio. If it is
not visible, Go to View -> Properties Window.
Select the button and view properties as follows.
Now set the text to 'Show' for the button.

6
Step 4: Writing the code
Double click on buttun1 to write the code
private void button1_Click(object sender, EventArgs e)
{
MessageBox.Show("Hello World!");
}
Step 5: Compile the code
To compile the code Go to Build -> Build HelloWorld
Step 6: Running the application
To run/execute the program press F5.

7
Running Application.
6- Create First Web application
Building Your First Web Application Project
Creating a New Project
Select File->New Project within the Visual Studio 2005 IDE. This will bring up the New Project
dialog. Click on the “Visual C#” node in the tree-view on the left hand side of the dialog box and
choose the "ASP.NET Web Application" icon:

8
Visual Studio will then create and open a new web project within the solution explorer. By default
it will have a single page (Default.aspx), an AssemblyInfo.cs file, as well as a web.config file. All
project file-meta-data is stored within a MSBuild based project file.

9
Opening and Editing the Page
Double click on the Default.aspx page in the solution explorer to open and edit the page. You can
do this using either the HTML source editor or the design-view. Add a "Hello world" header to the
page, along with a calendar server control and a label control (we'll use these in a later tutorial):
Build and Run the Project
Hit F5 to build and run the project in debug mode. By default, ASP.NET Web Application projects
are configured to use the built-in VS web-server when run. The default project templates will run
on a random port as a root site (for example: http://localhost:12345/):

10
You can end the debug session by closing the browser window, or by choosing the Debug->Stop
Debugging (Shift-F5) menu item.
Customizing Project Properties
ASP.NET Web Application Projects share the same configuration settings and behaviors as
standard VS 2005 class library projects. You access these configuration settings by right-clicking
on the project node within the Solution Explorer in VS 2005 and selecting the "Properties" context-
menu item. This will then bring up the project properties configuration editor. You can use this to
change the name of the generated assembly, the build compilation settings of the project, its
references, its resource string values, code-signing settings, etc:

11
ASP.NET Web Application Projects also add a new tab called "Web" to the project properties list.
Developers use this tab to configure how a web project is run and debugged. By default, ASP.NET
Web Application Projects are configured to launch and run using the built-in VS Web Server (aka
Cassini) on a random HTTP port on the machine.
This port number can be changed if this port is already in use, or if you want to specifically test and
run using a different number:

12
Alternatively, Visual Studio can connect and debug IIS when running the web application. To use
IIS instead, select the "Use IIS Web Server" option and enter the url of the application to launch,
connect-to, and use when F5 or Control-F5 is selected:

13
Then configure the url to this application in the above property page for the web project. When you
hit F5 in the project, Visual Studio will then launch a browser to that web application and
automatically attach a debugger to the web-server process to enable you to debug it.
Note that ASP.NET Web Application Projects can also create the IIS vroot and configure the
application for you. To do this click the "Create Virtual Directory" button.

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Introduction to C#
Comments
1- Single Line ( // )
Ex: int x,y,s;
S=x+y; // the sum of x,y
2- Multiple Line (/* */)
Ex: int x,y,s;
S=x+y; /* the sum
of x,y */
Arithmetic Operations
Operations Arithmetic in c#
Addition +
Subtraction -
Multiplication *
Division /
Modulus %
Precedence of Arithmetic Operations
( )
*,/,%
+,-
<,<=,>,>=
==,!=
=
Ex z = p * r ٪ q + w / x – y
(6) (1) (2) (4) (3) (5)
Ex y = a * x * x + b * x + c
(6) (1) (2) (4) (3) (5)

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Equality and Relational Operator
Standard Operator C# Operator Ex in C#
= == If (x==y)
≠ != If (x!=y)
> > If (x>y)
≥ >= If (x>=y)
< < If (x<y)
≤ <= If (x<=y)
Assignment operations
int c;
c=c+3; c+=3;
c ‫ــ‬ =3;
c*=3;
c/=3;
(var) = (var) (operator) (expiration)
If true
(var) (operator) = (expiration)
Increment and Decrement Operator
Operator Call Ex
++ Pre Increment ++ a
++ Post Increment a++
-- Pre Decrement --b
-- Post Decrement b--
Ex : int c=5;
MessageBox.Show(c); //5
MessageBox.Show(c++); // 5
MessageBox.Show(++c); // 6
C=5;
MessageBox.Show(c); // 5
MessageBox.Show(++c); // 6
MessageBox.Show(c); // 6

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Loop Statement in C#
For While Do-While
For (int ; condition ;
increment)
Ex :
For (int i=0;i<=5;i++)
Textbox1.text=textbox1.text+i;
0
1
2
3
4
5
While (condition)
State;
Ex :
int i=0;
While (i<=5)
{
Textbox1.text=textbox1.text+ i;
i i =i+1;
}
0
1
2
3
4
5
Do
{ State}
While (condition);
Ex :
int i=0;
do
{
i++;
} While (i<=5);
0
1
2
3
4
5
Declarations and types
1- Goals:
1-Learn C# program structure
2-Learn what comments are.
3-Know different types of C# data types
4- Learn what Variables are.
2- General Structure of a C# Program
Well, you have understand where to and how to execute your program. Each
program requires three important steps to do the work. Input, Process and Output. It
is the basic concept of almost all the programming language. It is also known as

17
I-P-O cycle. The program requires some input from the user. Next, the program
processes the input with programming language and finally shows the output.
The basic structure of c# program:
Using System;
namespace newproject
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
}
}
3- Create and run a GUI (Graphic user Interface) project
Step 1: Start Visual Studio
Open the Microsoft Visual Studio 2008.
Step 2: Create a new project
Go to File -> New Project, And then New Project Dialog Appears. In the New
Project Window, Select Visual C# as Project type and windows form Application as
the template.
Step 3: Writing the code
Under the standard structure of c# program Add the following code which you will
enter your name and your name will be displayed with some text message in the
form.

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using System;
namespace WindowsFormsApplication1
{
{
public Form1()
{
}
private void Form1_Load(object sender, EventArgs e)
{
textBox1.Text = "Hello Students";
}
}
}
Step 4: Run your application
Press F5
Step 5: Output:
4- Example1 Explanation:
using System;
It is used for including C# class library. C# has huge collection of classes and objects. If
you want to use those classes then you will have to include their library name in your
program.
string name; //Variable for storing string value
int name; // Variable for storing integer value

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.
Input: For storing values into the specific variables. Eg.
int a;
a=5;
string s;
s="Hello";
Output: For getting result from the specific operations. Eg.
int a;
a=5;
textbox1.text=Convert.Tostring(a);
5- Comments
The first line contains a comment. The characters // convert the rest of the line to a
comment.
// A Hello World! program in C#.
You can also comment out a block of text by enclosing it between the /* and */ characters.
This is shown in the following example.
/* A "Hello World!" program in C#.
This program displays the string "Hello World!" on the screen. */
6- C# Data Types
A complete detail of C# data types are mentioned below:
Data Types Size Values
sbyte 8 bit -128 to 127
byte 8 bit 0 to 255

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short 16 bit -32,768 to 32,767
ushort 16 bit 0 to 65,535
int 32 bit -2,147,483,648 to 2,147,483,647
uint 32 bit 0 to 4,294,967,295
long 64 bit -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
ulong 64 bit 0 to 18,446,744,073,709,551,615
char 16 bit 0 to 65535
float 32 bit -1.5 x 1045 to 3.4 x 1038
double 64 bit -5 x 10324 to 1.7 x 10308
decimal 128 bit -1028 to 7.9 x 1028
bool --- True or false
6- Example1: Write a program in c# to find the result of adding two values.
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
{
{
public Form1()
{
}
{

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int a, b,c;
a =Convert.ToInt32( textBox1.Text);
b =Convert.ToInt32( textBox2.Text);
c = a + b;
textBox3.Text = Convert.ToString(c);
}
}
}
OUTPIT:
7- Example2: Write a program in c# to find the result of multiplying two values.
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
{
int a, b,c;

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c = a * b;
} }}
OUTPUT:
8- Conversion
C# accepts string value by default. If you are using other value then you will have to
convert of specific data types.
num1 = int32.Parse(Console.ReadLine());
You can use the following method to convert one data type to another data type.
Integer = int32.parse() or Convert.ToInt32()
int=Convert.ToInt32(string);
String=Convert.ToString(integer);
Double=Convert.ToDouble();
Decimal=Convert.ToDecimal();
Byte=Convert.ToByte();

23
For Example:
{
int a, b,c;
c = a * b;
}
Beginning C# programming fundamentals
1- Name Spaces:
The namespace keyword is used to declare a scope that contains a set of related
objects. You can use a namespace to organize code elements and to create globally
unique types.
2- Conversion:
You can convert a string to a number by using methods in the Convert class. Such a
conversion can be useful when obtaining numerical input from a command line
argument, for example. The following table lists some of the methods that you can
use.

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2.1 Convert Class
Numeric Type Method
decimal ToDecimal(String)
float ToSingle(String)
double ToDouble(String)
short ToInt16(String)
int ToInt32(String)
long ToInt64(String)
Structure Conversion Method
Decimal static decimal Parse(string str)
Double static double Parse(string str)
Single static float Parse(string str)
Int64 static long Parse(string str)
Int32 static int Parse(string str)
Int16 static short Parse(string str)
UInt64 static ulong Parse(string str)
UInt32 static uint Parse(string str)
UInt16 static ushort Parse(string str)
Byte static byte Parse(string str)
bool static bool Parse(string str)
SByte static sbyte Parse(string str)

25
Example1:
3- Relational Operator:
In most cases, the Boolean expression, used by the if statement, uses relation
operators
string name;
int mark;
name ="Redwan"
mark = Int32.Parse(85);
textbox1.text=name;
textbox2.text=Convert.ToString(mark);

26
4- Boolean Expressions:
A Boolean expression is any variable or calculation that results in a true or false
condition.
5- Condition control structure
Thus far, within a given function, instructions have been executed sequentially, in the
same order as written. Of course that is often appropriate! On the other hands if you
are planning out instructions, you can get to a place where you say, “Hm, that
depends....”, and a choice must be made. The simplest choices are two-way: do one
thing is a condition is true, and another (possibly nothing) if the condition is not true.
5.1The if Statement
The if statement decides whether a section of code executes or not. The if statement
uses a Boolean to decide whether the next statement or block of statements executes.
The general C# if syntax is:

27
if (expression )
{Statement(s) for if-true}
Example2
:
5.2 if-else Statements
The general C# if-else syntax is
if (expression )
{Statement(s) for if-true}
else
{statement(s) for if-false}
Example3:
5.3 if-else-if Statements
if (expression_1)
{
statement;
statement;
etc.
}
Otherwise, if expression_2 is true these statements
are executed, and the rest of the structure is
ignored.
Insert as many else if clauses as necessary.
If expression_1 is true these statements are
executed, and the rest of the structure is ignored.
int x=2,y=4;
if(x>y)
MessageBox.Show("True");

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else if (expression_2)
{
statement;
statement;
etc.
}
else
{
statement;
statement;
etc
Example4:
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
{
These statements are executed if none of the
expressions above are true.
int x=2,y=4;
if(x>y)
else
MessageBox.Show("False");

29
int a, b, c;
a = Convert.ToInt32(textBox2.Text);
b = Convert.ToInt32(textBox3.Text);
if (Convert.ToInt32(textBox1.Text) == 1)
{
c = a + b;
}
else if (Convert.ToInt32(textBox1.Text)==2)
{
c=a-b;
textBox4.Text=Convert.ToString(c);
}
else if (Convert.ToInt32(textBox1.Text) == 3)
{
c = a * b;
}
else if (Convert.ToInt32(textBox1.Text) == 4)
{
c = a / b;
}
}
}
}
Example5 (Switch- Condition):
switch (value)
{
case value 1:
statements
break;
case value 2:

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statements
break;
}
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
{
int a, b, c;
a = Convert.ToInt32(textBox2.Text);
b = Convert.ToInt32(textBox3.Text);
switch (Convert.ToInt32(textBox1.Text))
{
case 1:
c = a + b;
break;
case 2:
c = a - b;
break;
case 3:
c = a * b;

31
break;
case 4:
c = a / b;
break;
} } } }
OUTPUT:
String Functions Definitions
Clone() Make clone of string.
CompareTo()
Compare two strings and returns integer value as output. It
returns 0 for true and 1 for false.
Contains()
The C# Contains method checks whether specified
character or string is exists or not in the string value.
EndsWith()
This EndsWith Method checks whether specified character
is the last character of string or not.
Equals()
The Equals Method in C# compares two string and returns
Boolean value as output.
GetHashCode() This method returns HashValue of specified string.
GetType() It returns the System.Type of current instance.
GetTypeCode() It returns the Stystem.TypeCode for class System.String.
IndexOf() Returns the index position of first occurrence of specified

32
character.
ToLower()
Converts String into lower case based on rules of the
current culture.
ToUpper()
Converts String into Upper case based on rules of the
current culture.
Insert()
Insert the string or character in the string at the specified
position.
IsNormalized()
This method checks whether this string is in Unicode
normalization form C.
LastIndexOf()
Returns the index position of last occurrence of specified
character.
Length It is a string property that returns length of string.
Remove()
This method deletes all the characters from beginning to
specified index position.
Replace() This method replaces the character.
Split() This method splits the string based on specified value.
StartsWith()
It checks whether the first character of string is same as
specified character.
Substring() This method returns substring.
ToCharArray() Converts string into char array.
Trim()
It removes extra whitespaces from beginning and ending of
string.
using System;
using System.Data;
using System.Linq;

33
using System.Text;
{
{
public Form1()
{
}
{
string s,fn, ln;
fn = textBox1.Text;
ln = textBox2.Text;
s = comboBox1.Text;
switch (s)
{
case "Clone":
textBox3.Text=Convert.ToString( fn.Clone());
textBox4.Text=Convert.ToString(ln.Clone());
break;
case "CompareTo":
int b = fn.CompareTo(ln);
if (b == 0)
MessageBox.Show("False");
else if (b == 1)
break;
case "Contains":
MessageBox.Show(Convert.ToString( fn.Contains("W")));
break;

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case "EndsWith":
MessageBox.Show(Convert.ToString( fn.EndsWith("d")));
break;
case "Equals":
MessageBox.Show(Convert.ToString( fn.Equals(ln)));
break;
case "GetHashCode":
textBox3.Text =Convert.ToString( fn.GetHashCode());
textBox4.Text =Convert.ToString( ln.GetHashCode());
break;
case "GetType":
textBox3.Text = Convert.ToString(fn.GetType ());
textBox4.Text = Convert.ToString(ln.GetType ());
break;
case "GetTypeCode":
textBox3.Text = Convert.ToString(fn.GetTypeCode ());
textBox4.Text = Convert.ToString(ln.GetTypeCode ());
break;
case "IndexOf":
textBox3.Text = Convert.ToString(fn.IndexOf("e"));
textBox4.Text = Convert.ToString(ln.IndexOf("o"));
break;
case "ToLower":
textBox3.Text = Convert.ToString(fn.ToLower());
textBox4.Text = Convert.ToString(ln.ToLower());
break;
case "ToUpper":
textBox3.Text = Convert.ToString(fn.ToUpper());
textBox4.Text = Convert.ToString(ln.ToUpper());
break;
case "Insert":
textBox3.Text = Convert.ToString(fn.Insert(0, "Hi "));
textBox4.Text = Convert.ToString(ln.Insert(0, " Hi "));

35
break;
case "IsNormalized":
MessageBox.Show(Convert.ToString(fn.IsNormalized()));
break;
case "LastIndexOf":
textBox3.Text = Convert.ToString(fn.LastIndexOf("o"));
textBox4.Text = Convert.ToString(ln.LastIndexOf("s"));
break;
case "Length":
textBox3.Text = Convert.ToString(fn.Length);
textBox4.Text = Convert.ToString(ln.Length);
break;
case "Remove":
textBox3.Text = Convert.ToString(fn.Remove(5));
textBox4.Text = Convert.ToString(ln.Remove(0,4));
break;
case "Replace":
textBox3.Text = Convert.ToString(fn.Replace("o", "*"));
textBox4.Text = Convert.ToString(ln.Replace("w", "*"));
break;
case "Split":
string[] split1 = fn.Split(new char[] { 'o' });
textBox3.Text = split1[0];
string[] split2 = ln.Split(new char[] { 'd' });
textBox4.Text = split2[1];
break;
case "StartsWith":
textBox3.Text=Convert.ToString(fn.StartsWith("O"));
textBox4.Text = Convert.ToString(ln.StartsWith("W"));
break;
case "SubString":
textBox3.Text = Convert.ToString(fn.Substring(2, 5));
textBox4.Text = Convert.ToString(ln.Substring(4, 5));

36
break;
case "ToCharArray":
char[] s1 = fn.ToCharArray();
char [] s2= ln.ToCharArray();
for (int i = 0; i < fn.Length; i++)
{
textBox3.Text = textBox3.Text + s1[i];
}
for (int i = 0; i < ln.Length ; i++)
{
textBox4.Text = textBox4.Text + s2[i];
}
break;
case "Trim":
textBox3.Text = Convert.ToString(fn.Trim());
textBox4.Text = Convert.ToString(ln.Trim(new char[] {'s'}));
break;
}
}
}
}

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Loop control structure
1- Goals:
In this chapter you will learn:
• What is Loop Constructs in C#?
• How many types of looping statements in C sharp?
• How to use loop constructs in Programming?
H.M) Write a program in C# to enter 10 degrees, then find the Grade for each of
them.
2- Loop constructs
The loop constructs is used to execute a block of code until the condition becomes
expired. Loop constructs in C#, saves the programmer from writing code multiple
times that has repetitive in nature.
2.1 For Loop:

38
Example 1:
OUTPUT
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
{
string a;
a = "aa";
for (int i = 0; i < 5; i++)
{
textBox1.Text = textBox1.Text + a;
textBox1.AppendText(Environment.NewLine);
}
}
}
}

39
Example 2:
OUTPUT
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
{
int i,j;
for (i = 0; i < 5; i++)
{
for (j = 0; j < 5; j++)
textBox1.Text = textBox1.Text + i+j+" ";
}
}
}
}
H.W) Find the main diagonal, secondary diagonal, swap the rows to columns…

40
2.2 While Loop:
Example 3:
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
{
int num, r, i;
num = Convert.ToInt32(textBox1.Text);
i = 1;
while (i <= 10)
{

41
r = num * i;
textBox2.Text = textBox2.Text + r + "=" + num + "*" + i;
i += 1;
}
}
}
}
2.3 Do-While Loop:
Note: must put semi-colon(;) at the end of while condition in do-while loop.
Example 4:
{
int num, r, i;
num = Convert.ToInt32(textBox1.Text);
i = 1;
do
{
r = num * i;
textBox2.Text = textBox2.Text + r + "=" + num + "*" + i;
i += 1;
} while (i <= 10);
}
Q) What's the different between the (While and Do_While loop)?

42
Break:
The break is use in for, while, do-while, switch case. Break statement is used to
terminating the current flow of program and transfer controls to the next execution.
Continue:
The continue is use in for, while, do-while. The continue statements enables you to
skip the loop and jump the loop to next iteration.
continue break
for (int i=0;i<=5;i++)
{
if(i<=3)
continue ;
textBox1.Text = textBox1.Text + i;
}
4
5
for (int j = 0; j <= 5; j++)
{
if (j >= 3)
break ;
textBox2.Text = textBox2.Text + j;
}
0
1
2
EX:
Break
for (int i=1; i<=7;i++)
{
If (i==5)
Break;
}
Output
1 2 3 4
Continue

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For (int i=1; i<=7;i++)
{ if (i==5)
Continue;
}
Output
1234 678910
Build_in and User_define C# Methods
1- Method (= Function)
A method is a group of statements that together perform a task. It combines related code together and
makes program easier. Every C# program has at least one class with a method named Main.
2- Method Types:
1. Built in: the methods that the language provides. Such as Math class provide the following
methods:
Abs (x) exp (x) tan (x)
Cos (x) pow (x,y) log (x)
Sin (x) max (x,y) Sqrt (x)
Log10, max, min, round, sqrt.
Example:
Math.abs(x);
Textbox1.text=Convert.ToString(math.abs(-10));
Math.cos(x);

44
2. User defines: the methods that the user defines and call.
Example:
int sum (int x , int y)
{int s=x+y;
Return (s);}
3- Defining Methods in C# and calling techniques:
When you define a method, you basically declare the elements of its structure. The syntax for
defining a method in C# is as follows:
Following are the various elements of a method:
• Access Specifier: This determines the visibility of a variable or a method from
another class.
• Return type: A method may return a value. The return type is the data type of the
value the method returns. If the method is not returning any values, then the return
type is void.
• Method name: Method name is a unique identifier and it is case sensitive. It
cannot be same as any other identifier declared in the class.
• Parameter list: Enclosed between parentheses, the parameters are used to pass
and receive data from a method. The parameter list refers to the type, order, and
number of the parameters of a method. Parameters are optional; that is, a method
may contain no parameters.
< Access Specifier> < Return Type> < Method Name> (Parameter list)
{
Body
}

45
• Method body: This contains the set of instructions needed to complete the
required activity.
Example:
public void add()
{
Body
}
In the preceding example, the public is an access specifier, void is a return data type
that return nothing and add() is a method name. There is no parameter define in
add() method.
If the function returns interger value, then you can define function as follow:
public int add()
{
Body
}
If the function is returning string value, then you can define function as follow:
public string printname()
{
Body
}
You must remember, whenever use return data type with method, must return value
using return keyword from body. If you don’t want to return any value, then you can
use void data type.

46
Ex:
Class program
{
public int sqr(int a)
{
return (a * a);
}
{
int b;
textBox2.Text = Convert.ToString(sqr(b));
}
}
4- Passing arguments:
pass by value Pass by reference
static int sqr(int x)
{
return ( x * x);
} ----------
Output
- Before call x is 5
- After call x is 5
static int sqr2(ref int x)
{
return x * x;
}
----------
Output
- Before call x is 5
- After call x is 25

47
Method overload
1. C# enable several methods of same name to be defined in same class as long as
these method have different sets of parameters (number of parameter , type of
parameter , order of parameter ) this is called method overloaded .
2. Method overloading commonly is used to create several methods with same name
that perform similar tasks, but on different data types.
Ex:
Static int squire (int x)
{
return (x*x);
}
Static double squire (double x)
{
return (x*x);
}
static void main ( )
{
int y = 2;
double z=12.1;
textBox1.Text = Convert.ToString(squire(y));
textBox1.Text = Convert.ToString(squire(z));
}
Output
- The squire of int 2 is 4.
- The squire of double 2.1 is 4.41.
Note: This is called overload method.

48
Arrays (declaration 1_D, 2_D, initialization)
1- Array:
Sometimes, you need to declare multiple variable of same data type. It is complex
and time consuming process. Just for an example, you have to declare 100 integer
type of variable then what would you do? Will you declare variable as follow:
int num1,num2,num3,num4,num5,num6,num7,num8.... num100;
It is not a suitable way to declare multiple variable of same data type. To overcome
this situation, array came alive. An array is a collection of same data type. If you
have to declare 100 variable of same data type in C#, then you can declare and
initialize an array as follow.
int[] num = new int[100];
2- Structure of C# array:
To understand concept of array, consider the following example. What happens in
memory when we declare an integer type array?
int[] num = new int[6];
Num Array:

49
3- Declaration and Initialization of Array:
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
{
int[] array=new int [5];
array[0] = 3;
array[1] = 6;
array[2] = 2;
array[3] = 7;
array[4] = 9;
for (int i = 0; i < 5; i++)
{
textBox1.Text = textBox1.Text + array[i];
}
}
}
}

50
4- Storing value directly in C# program:
In your program, you can directly store value in array. You can store value in array
by two ways.
i. Inline:
int[] arr =new int[5] { 3, 6, 2, 7, 9 };
ii. Index:
int[] arr = new int[5]
arr[0] = 3;
arr[1] = 6;
arr[2] = 2;
arr[3] = 7;
arr[4] = 9;
iii. Users input:
using System;
using System.Data;
using System.Linq;
using System.Text;
using Microsoft.VisualBasic;
{
{
public Form1()
{
}

51
{
int[] array2 = new int[10];
for (int i = 0; i < 10; i++)
{
array2[i] = Convert.ToInt32(Interaction.InputBox("Enter The
array elements", "Input Box", "Write Here", 75, 75));
textBox1.Text = textBox1.Text + array2[i];
}
}
}
}
Hint: To define InputBox, you have to Add reference from .Net-> Microsoft.Visual Basic,
then write it's library.

52
5- Accessing value from array:
You can access array’s value by its index position. Each index position in array
refers to a memory address in which your values are saved.
int[] arr=new int[6];
int num1, num2;
num1 = arr[1] * arr[3];
It is same as:
num1 = 23 * 9; Because, arr[1] refers to the value 23 and arr[3] refers to the value 9.
If you are required to access entire value of an array one after another, then you can
use loop constructs to iterate through array.
Example3:
using System;
using System.Data;
using System.Linq;
using System.Text;
using Microsoft.VisualBasic;
{
{
public Form1()
{
}

53
{
int[] id = new int[3];
string[] name = new string[3];
int i, j = 0;
string f;
for (i = 0; i < 3; i++)
{
id[i] = Convert.ToInt32(Interaction.InputBox("Enter the id",
"InputBox", "Enter Here", 75, 75));
name[i] = Interaction.InputBox("Enter the name", "InputBox",
"Enter Here", 75, 75);
}
f = Interaction.InputBox("Enter the name to find", "InputBox",
"Enter Here", 75, 75);
for (i = 0; i < 3; i++)
{
if (name[i] == f)
{
MessageBox.Show(Convert.ToString(id[i]), "The Id is:");
j++;
}
}
if (j == 0)
MessageBox.Show("Not Found");
}
}
}
Hint: To define InputBox, you have to Add reference from .Net-> Microsoft. Visual Basic,
then write it's library.

54
Array dimensions
A. One dimensional:
The one dimensional array or single dimensional array in C# is the simplest type of
array that contains only one row for storing data. It has single set of square bracket
(“[]”). To declare single dimensional array in C#, you can write the following code.
Example4:
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
{

55
string[] books = new string[5] { "C#", "VB", "JAVA", "C++", "MATLAB"
};
textBox1.Text = "First Second Third Four Five";
textBox1.Text = textBox1.Text + "_______________________________";
for (int i = 0; i < 5; i++)
{
textBox1.Text = textBox1.Text + books[i] + " ";
}
}
}
}
OUTPUT:
B. Multi-dimensional array:
The multi-dimensional array in C# is such type of array that contains more than one
row to store data on it. The multi-dimensional array is also known as rectangular array
in c sharp because it has same length of each row. It can be two dimensional array or
three dimensional array or more. It contains more than one coma (,) within single
rectangular brackets (“[ , , ,]”). To storing and accessing the elements from

56
multidimensional array, you need to use nested loop in program. The following
example will help you to figure out the concept of multidimensional array.
Example5:
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
{

57
string[,] books = new string[3,3]{ { "C#", "VB", "JAVA"},{".NET",
"C++", "DB" },{"SQL","HTML","XML"}};
textBox1.Text = "First Second Third ";
textBox1.Text = textBox1.Text + "___________________________";
for (int i = 0; i < 3; i++)
{
for (int j = 0; j < 3; j++)
{
textBox1.Text = textBox1.Text + books[i, j] + " ";
}
}
}
}
}
OUTPUT:

58
Passing array
An array can also be passed to method as argument or parameter. A method process
the array and returns output. Passing array as parameter in C# is pretty easy as passing
other value as parameter. Just create a function that accepts array as argument and then
process them. The following demonstration will help you to understand how to pass
array as argument in C# programming.
Example4:
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
public void printarray(int[] print)
{
int i;
for (i = 0; i < 5; i++)
{
textBox1.Text = textBox1.Text + print[i];
}
}
{
int[] num = new int[5] { 2, 4, 6, 8, 10 };
printarray(num);
}
} }

59
Most common properties of Array class
Properties Explanation Example
Length Returns the length of array. Returns integer value. int i = arr1.Length;
Rank
Returns total number of items in all the dimension. Returns
integer value.
int i = arr1.Rank;
IsFixedSize
Check whether array is fixed size or not. Returns Boolean
value
bool i = arr.IsFixedSize;
IsReadOnly
Check whether array is ReadOnly or not. Returns Boolean
value
bool k =
arr1.IsReadOnly;
H.M) Apply these properties in arrays (Max, Min, Sum, Average, First, Last).
Most common functions of Array class
Function Explanation Example
Sort Sort an array Array.Sort(arr);
Clear Clear an array by removing all the items Array.Clear(arr, 0, 3);
GetLength Returns the number of elements arr.GetLength(0);
GetValue Returns the value of specified items arr.GetValue(2);
IndexOf Returns the index position of value Array.IndexOf(arr,45);
Copy Copy array elements to another elements Array.Copy(arr1,arr1,3);
Example5:
using System;
using System.Data;
using System.Linq;
using System.Text;

60
{
{
public Form1()
{
}
public void arr_mul(int[] array1)
{
int i;
double mul = 1;
for (i = 0; i < 5; i++)
{
textBox8.Text = textBox8.Text + array1[i];
mul *= array1[i];
}
for (i = 0; i < 5; i++)
{
textBox9.Text = textBox9.Text+array1[i].ToString();
}
Array.Sort(array1);
for(i=0;i<5;i++)
{
textBox6.Text = textBox6.Text + array1[i].ToString();
}
textBox11.Text = mul.ToString() ;
}
{
int[] arr1 = new int[5] { 7, 3, 12, 8, 11 };
int[] arr2 = new int[5];
int len, r,gl,gt;
bool fixedsize, read_only;
Array.Copy(arr1, arr2, arr1.Length);
len = arr1.Length;
textBox1.Text = len.ToString();
r=arr1.Rank;
textBox2.Text = r.ToString();

61
fixedsize = arr1.IsFixedSize;
textBox3.Text = fixedsize.ToString();
read_only = arr1.IsReadOnly;
textBox4.Text = read_only.ToString();
gl=arr1.GetLength(0);
textBox5.Text = gl.ToString();
textBox10.Text = arr1.Sum().ToString();
gt=Convert.ToInt32(textBox7.Text);
textBox8.Text = arr1.GetValue(gt).ToString();
arr_mul(arr1);
}
}
}
Q) Write a program in C# to find the following in array, (Copy, Reverse, Find, Resize).

62
Events
TextBox lets users type letters and enter data. It is part of the Windows Forms platform
and is used with C# code. It is added with the Visual Studio designer. Many events and
properties are available on this control.
Intro. First, the TextBox will take care of reading the keys and displaying the text. But
it will not do anything with the text it accepts. You will need to access the text from the
TextBox based on custom logic rules.
Events. In Visual Studio the lightning bolt symbol describes event handlers. Windows
Forms programs are primarily event-based, which means you can use the lightning bolt
icon in the Properties dialog to add the most important event handlers.

63
TextChanged. You can use the TextChanged event to modify another part of your
program when the user types text into a TextBox. The TextChanged event is only
triggered when the text is changed to something different, not changed to the same
value.
This program assigns the base window's title text to the text typed in by the user to the
TextBox. This makes the base window's title reflect the user's input. The Windows
taskbar will also show this text.
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
private void textBox1_TextChanged(object sender, EventArgs e)
{
//
// This changes the main window text when you type into the TextBox.
//
this.Text = textBox1.Text;
}
}
}

64
KeyDown. You can read key down events in the TextBox control in Windows Forms.
The Windows Forms system provides several key-based events. This tutorial uses the
KeyDown event handler which is called before the key value actually is painted.
You can cancel the key event in the KeyDown event handler as well, although this is
not demonstrated. The program will display an alert when the Enter key is pressed. An
alternative alert message when the Escape key is pressed.
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
//
// Detect the KeyEventArg's key enumerated constant.
//
if (e.KeyCode == Keys.Enter)
{
MessageBox.Show("You pressed enter! Good job!");
}
else if (e.KeyCode == Keys.Escape)
{
MessageBox.Show("You pressed escape! What's wrong?");
}
}
}
}

65
Multiline. You can use the Multiline property on the TextBox control to create a longer
text input area. The TextBox control has performance problems with large amounts of
text. But for shorter multiline input boxes, this is useful.
Using TextBox with button. The screenshot shows a TextBox that was modified in the designer to
have its multiline property set to true. The form also has a Button control with the text "Save" on it.
Files. You can make the TextBox control do something that could be useful in a real program:
write the file to disk. This is essentially a primitive word processor. But don't use it to write
anything important yet.
After adding the multiline TextBox, we can add a Button and add the button1_Click event
handler. In that event handler, we can access the TextBox Text property and write it to a location
on the hard disk.

66
using System;
using System.IO;
{
{
public Form1()
{
}
{
//
// This is the button labeled "Save" in the program.
//
File.WriteAllText("C:demo.txt", textBox1.Text);
}
}
}
Result
This is some text
written for the textbox tutorial
The example calls the File.WriteAllText method. This method will take the string data
pointed to by the string reference returned by the Text property. It then actually writes
that to the physical hard disk on the computer.
TextBox.AppendText. TextBox provides the AppendText method. This method
appends lines of text to a TextBox control. With it we have to deal with newlines and
avoid extra line breaks. We are using the TextBox in multiline mode.
Example. We can append text to a TextBox with the method AppendText. However,
that will not append a newline or line feed to the end of the text, so when you call
textBox1.AppendText("text") two times, the text will be on the same line.
private void Test()
{
for (int i = 0; i < 2; i++)
{
textBox1.AppendText("Some text");
}
}

67
Example 2. You can append lines by using Environment.NewLine and then adding
some conditional logic to determine the first and last lines. This is better than any
version of AppendLine or AppendText. It doesn't add extra newlines.
{
private void AppendTextBoxLine(string myStr)
{
if (textBox1.Text.Length > 0)
{
}
textBox1.AppendText(myStr);
}
private void TestMethod()
{
for (int i = 0; i < 2; i++)
{
AppendTextBoxLine("Some text");
}
}
}
Contents of TextBox
Some text
Some text
Example 3. If you don't check the length of the Text in the TextBox, you will have
unwanted line breaks in your TextBox. However, for less important code, you may
prefer the slightly simpler method. The following code always appends newlines.
public partial class Browser : Form
{
private void Test()
{
// Will leave a blank line on the end.
for (int i = 0; i < 2; i++)
{
textBox1.AppendText("Some text" + Environment.NewLine);
}
// Will leave a blank line on the start.
for (int i = 0; i < 2; i++)
{
textBox1.AppendText(Environment.NewLine + "Some text");
}
} }

68
ListBox stores several text items. It can interact with other controls, including Button
controls. We use this control in Windows Forms. In the example program it interacts
with two Buttons—through the Button Click event handler.
Tutorial. First, create a new Windows Forms C# project, and then open the Toolbox
and double-click on the ListBox item. This will insert a new ListBox into your Windows
Forms designer. If you want to use Buttons with the ListBox, add those too.
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
List<string> _items = new List<string>(); // <-- Add this
public Form1()
{
_items.Add("One"); // <-- Add these
_items.Add("Two");
_items.Add("Three");
listBox1.DataSource = _items;
}
}
}

69
In this example, we see a List of strings at the class level. This is a good place to store
the lines you want to show in your ListBox. In the constructor, we add three elements to
the List.
DataSource:At the final point in the constructor, we assign the DataSource from the
listBox1 to the new List.
Button. Go back to your Designer window in Visual Studio where you see the image of
the Form. Select the buttons and then add the text "Add" and "Remove" to their Text
properties in the Properties pane.
Add event handlers. Here we double-click on each button in the Designer. You will be
taken to the C# code view and a new event handler will have been inserted. In these
event handlers, we manipulate the List and refresh the ListBox.
{
// The Add button was clicked.
_items.Add("New item " + DateTime.Now.Second); // <-- Any string you want
// Change the DataSource.
listBox1.DataSource = null;
}
{
// The Remove button was clicked.
int selectedIndex = listBox1.SelectedIndex;
try
{
// Remove the item in the List.
_items.RemoveAt(selectedIndex);
}
catch
{
}
}

70
Form. Here we see the complete code for the Form.cs file, which acts on the ListBox
and two Buttons in the Designer. It shows how to add and remove items to the ListBox
with the buttons.
using System;
{
{
List<string> _items = new List<string>();
public Form1()
{
_items.Add("One");
_items.Add("Two");
_items.Add("Three");
}
{
_items.Add("New item " + DateTime.Now.Second);
// Change the DataSource.
}
{
int selectedIndex = listBox1.SelectedIndex;
try
{
// Remove the item in the List.
_items.RemoveAt(selectedIndex);
}
catch
{
}

71
}
}
}
Enabled. You can easily change the Enabled state of your Add and Remove buttons by
setting the Enabled property equal to false or true when the List is full or empty. This
example demonstrates setting Enabled.
{
// ...
button2.Enabled = true;
}
{
// ....
if (listBox1.Items.Count == 0)
{
button2.Enabled = false;
}
}
In this example, there are two button click event handlers. Button1 is the Add button,
so it always sets the Enabled property of Add to true. Button2 is the Remove button, so
it is disabled when there are no items in the ListBox.
ComboBox is a combination TextBox with a drop-down. Its drop-down list presents
preset choices. The user can type anything into the ComboBox. Alternatively, he or she
can select something from the list.
Example. To begin, please create a new Windows Forms application and add a
ComboBox to it. You can then right-click on the ComboBox and add the
SelectedIndexChanged and TextChanged event handlers in the Properties dialog.
This program shows how when you change the text by typing in the ComboBox or by

72
clicking on the list of Items, the event handlers are triggered. Please see the section on
the Items property before running the program.
using System;
{
{
public Form1()
{
}
int _selectedIndex;
string _text;
private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
// Called when a new index is selected.
_selectedIndex = comboBox1.SelectedIndex;
Display();
}
private void comboBox1_TextChanged(object sender, EventArgs e)
{
// Called whenever text changes.
_text = comboBox1.Text;
Display();
}
void Display()
{
this.Text = string.Format("Text: {0};
SelectedIndex: {1}",_text,_selectedIndex);
}
}
}
Text. The Text property of the ComboBox functions much like the Text property of a
TextBox. If you assign to the Text property, the current value in the ComboBox will
change. You can also read the Text property and assign string variables to it.
Items. The Items property contains the strings that are found in the drop-down part of
the ComboBox. You can type the Items line-by-line into Visual Studio through the
Items dialog, or you can dynamically add them during runtime.
To add Items, call the Add method: use the syntax comboBox1.Add("Value"). You can
also Clear the ComboBox with Clear().

73
RadioButton allows distinct selection of several items. In each group of RadioButtons,
only one can be checked or selected. Conceptually, this control implements an exclusive
selection. CheckBoxes allow multiple selections at once.
Steps. To begin, you should make a new Windows Forms application in Visual Studio,
and then you can add GroupBox (or Panel) controls to it. In these controls, you can nest
RadioButton instances.
By using this nesting strategy , you can have multiple groups of RadioButtons on a
single form.
You may want to add the CheckedChanged event handler on your RadioButtons.
You can actually have all the RadioButtons point to the same CheckedChanged event
handler using the event window in Visual Studio.
using System;
{
{
public Form1()
{
}
private void radioButton1_CheckedChanged(object sender, EventArgs e)
{
// Executed when any radio button is changed.
// ... It is wired up to every single radio button.
// Search for first radio button in GroupBox.
string result1 = null;
foreach (Control control in this.groupBox1.Controls)
{
if (control is RadioButton)

74
{
RadioButton radio = control as RadioButton;
if (radio.Checked)
{
result1 = radio.Text;
}
}
}
// Search second GroupBox.
string result2 = null;
foreach (Control control in this.groupBox2.Controls)
{
if (control is RadioButton)
{
RadioButton radio = control as RadioButton;
if (radio.Checked)
{
result2 = radio.Text;
}
}
}
this.Text = result1 + " " + result2;
}
}
}
In the example, we wired up all six RadioButtons to the
radioButton1_CheckedChanged event handler. Thus, whenever the user clicks or
changes the selection on the form, the above method will be executed.
ErrorProvider simplifies and streamlines error presentation. It is an abstraction that
shows errors on your form. It does not require a lot of work on your part. This is its key
feature.
Start. To start, please open the Toolbox pane in Visual Studio. Find and double-click on
the ErrorProvider icon. This will insert the errorprovider1 into the tray at the bottom of
the screen. You can change properties on the ErrorProvider instance by right-clicking on
it and selecting Properties.

75
Example. We start with the basics. We must activate the ErrorProvider in our Windows
Forms program. The ErrorProvider won't initiate any actions. It will be invoked through
other event handlers in the program.
In the example, we have a TextBox control and a TextChanged event handler on that
control. When the TextChanged event handler is triggered, we check to see if a digit
character is present.
If one is not, we activate an error through the ErrorProvider. Otherwise we clear the
ErrorProvider.
using System;
{
{
public Form1()
{
}
{
// Determine if the TextBox has a digit character.
string text = textBox1.Text;
bool hasDigit = false;
foreach (char letter in text)
{
if (char.IsDigit(letter))
{
hasDigit = true;
break;
}
}
// Call SetError or Clear on the ErrorProvider.
if (!hasDigit)
{
errorProvider1.SetError(textBox1, "Needs to contain a digit");
}
else
{
errorProvider1.Clear();
}
}
}
}

76
Using SetError method. The first argument of SetError is the identifier of the TextBox
control. The second argument is the error message itself. The first argument tells the
ErrorProvider where to draw the error sign.
Using Clear method. It is also important that you use the Clear method when
appropriate. If a digit was located, we simply remove the error sign from the user
interface. This instantly tells our user that no error is still present.
StatusStrip. A StatusStrip displays window status. It is usually at the bottom of a
window. We use a ToolStripStatusLabel hyperlink in the C# Windows Forms status bar.
Intro. We see an example of StatusStrip in Windows Forms, with tips on how to use its
properties. We introduce some parts of the Windows Forms program.
Some notes. There are other controls such as LinkLabel that you can use for links. But
this article is about my favorite way, the hyperlink in the status bar.
StatusStrip. The StatusStrip is a control in your Toolbox in Visual Studio. Double click
on its icon and then it will appear in the tray at the bottom of the Visual Studio window.
Items:Select the status strip control on your form, and in the Properties pane look
through the entries there and select Items.
Labels:In the Items window you can add things to the StatusStrip. Add new
ToolStripStatusLabels and a hyperlink.
Steps. I will assume you already have a StatusStrip. There are a few important things.
All of the items will be squished to the left of the status strip by default.
We can change this, and right-align a label. Here are the steps required to configure the
StatusStrip.
Spring:To right-align things on a StatusStrip we add a "spring" in between the left and
right items.
First step. Please open the Items dialog in Visual Studio. On your StatusStrip, open the
Items Collection Editor dialog in the A-Z listing.
Second, add some items. Leave the Status Label dropdown selected and click on the
big Add button. You can also add other types of controls to your status strip here.
To add a hyperlink, you can use a regular status label. You can make it a hyperlink later.
Third, add a ToolStripStatusLabel with "Spring" set to true. Put it after the leftmost
(first) status item. Add another status label after it. This will right-align the third status
label.
On the right side of the Items Collection Editor dialog, you will see another grid list.
Scroll to Text and type in the text of your link. Set the IsLink property to true.
Hyperlink. Double-click on the ToolStripStatusLabel you want to turn into a hyperlink.
We must use the Click event handler to make the status item do something when it is
clicked.

77
Process:To start a web browser, we will need to use the Process.Start method in
System.Diagnostics.
In the new Click event handler, add the inner line here. You can directly access
System.Diagnostics.
private void toolStripStatusLabel_Click(object sender,EventArgs e)
{
// Launch any website.
// ... You should change the URL!
System.Diagnostics.Process.Start("http://www.any.com/");
}
Background Color and Foreground Color
You can set background color and foreground color through property window and
programmatically.
textBox1.BackColor = Color.Blue;
textBox1.ForeColor = Color.White;
Textbox BorderStyle
You can set 3 different types of border style for textbox, they are None, FixedSingle and
fixed3d.
textBox1.BorderStyle = BorderStyle.Fixed3D;
TextBox Events
Keydown event
You can capture which key is pressed by the user using KeyDown event

78
TextChanged Event
When user input or setting the Text property to a new value raises the TextChanged
event
Textbox Maximum Length
Sets the maximum number of characters or words the user can input into the text box
control.
textBox1.MaxLength = 40;
Textbox ReadOnly
When a program wants to prevent a user from changing the text that appears in a text
box, the program can set the controls Read-only property is to True.
textBox1.ReadOnly = true;
Multiline TextBox
You can use the Multiline and ScrollBars properties to enable multiple lines of text to be
displayed or entered.
textBox1.Multiline = true;
Textbox passowrd character
TextBox controls can also be used to accept passwords and other sensitive information.
You can use the PasswordChar property to mask characters entered in a single line
version of the control
textBox1.PasswordChar = '*';
The above code set the PasswordChar to * , so when the user enter password then it
display only * instead of typed characters.

79
How to Newline in a TextBox
You can add new line in a textbox using many ways.
textBox1.Text += "your text" + "rn";
or
textBox1.Text += "your text" + Environment.NewLine;
using System;
{
{
public Form1()
{
}
{
textBox1.Width = 250;
textBox1.Height = 50;
textBox1.Multiline = true;
textBox1.BackColor = Color.Blue;
textBox1.ForeColor = Color.White;
textBox1.BorderStyle = BorderStyle.Fixed3D;
}
{
string var;
var = textBox1.Text;
MessageBox.Show(var);
}
}
}
You can use Regular Expression to validate a Textbox to enter number only.
System.Text.RegularExpressions.Regex.IsMatch(textBox1.Text, "[ ^ 0-9]")

80
The following method also you can force your user to enter numeric value only.
if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar))
{
e.Handled = true;
}
If you want to allow decimals add the following to the above code.
if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && (e.KeyChar != '.'))
{
e.Handled = true;
}
using System;
using System.Data;
using System.Linq;
using System.Text;
{
{
public Form1()
{
}
{
if (System.Text.RegularExpressions.Regex.IsMatch(textBox1.Text, " ^ [0-9]"))
{
textBox1.Text = "";
}
}
private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && (e.KeyChar != '.'))
{
e.Handled = true;
}
}
}
}

81
C# ProgressBar Control
A progress bar is a control that an application can use to indicate the progress of a
lengthy operation such as calculating a complex result, downloading a large file from
the Web etc.
ProgressBar controls are used whenever an operation takes more than a short period of
time. The Maximum and Minimum properties define the range of values to represent the
progress of a task.
Minimum : Sets the lower value for the range of valid values for progress.
Maximum : Sets the upper value for the range of valid values for progress.
Value : This property obtains or sets the current level of progress.
By default, Minimum and Maximum are set to 0 and 100. As the task proceeds, the
ProgressBar fills in from the left to the right. To delay the program briefly so that you
can view changes in the progress bar clearly.
The following C# program shows a simple operation in a progressbar.
using System;
{
{
public Form1()
{
}
{
int i;
progressBar1.Minimum = 0;
progressBar1.Maximum = 200;
for (i = 0; i <= 200; i++)

82
{
progressBar1.Value = i;
}
}
}
}
C# DateTimePicker Control
The DateTimePicker control allows you to display and collect date and time from the
user with a specified format.
The DateTimePicker control has two parts, a label that displays the selected date and a
popup calendar that allows users to select a new date. The most important property of
the DateTimePicker is the Value property, which holds the selected date and time.
dateTimePicker1.Value = DateTime.Today;
The Value property contains the current date and time the control is set to. You can use
the Text property or the appropriate member of Value to get the date and time value.
DateTime iDate;
iDate = dateTimePicker1.Value;

83
The control can display one of several styles, depending on its property values. The
values can be displayed in four formats, which are set by the Format property: Long,
Short, Time, or Custom.
dateTimePicker1.Format = DateTimePickerFormat.Short;
using System;
{
{
public Form1()
{
}
{
dateTimePicker1.Format = DateTimePickerFormat.Short;
dateTimePicker1.Value = DateTime.Today;
}
{
DateTime iDate;
iDate = dateTimePicker1.Value;
MessageBox.Show("Selected date is " + iDate);
}
}
}
C# Menu Control
A Menu on a Windows Form is created with a MainMenu object, which is a collection
of MenuItem objects. MainMenu is the container for the Menu structure of the form and
menus are made of MenuItem objects that represent individual parts of a menu.
You can add menus to Windows Forms at design time by adding the MainMenu
component and then appending menu items to it using the Menu Designer.

84
After drag the Menustrip on your form you can directly create the menu items by type a
value into the "Type Here" box on the menubar part of your form. If you need a
seperator bar , right click on your menu then go to insert->Seperator.

85
After creating the Menu on the form , you have to double click on each menu item and
write the programs there depends on your requirements. The following C# program
shows how to show a messagebox when clicking a Menu item.
using System;
{
{
public Form1()
{
}
private void menu1ToolStripMenuItem_Click(object sender, EventArgs e)
{
MessageBox.Show("You are selected MenuItem_1");
}
}
}
C# Color Dialog Box
There are several classes that implement common dialog boxes, such as color selection ,
print setup etc.
A ColorDialog object is a dialog box with a list of colors that are defined for the display
system. The user can select or create a particular color from the list, which is then

86
reported back to the application when the dialog box exits. You can invite a color dialog
box by calling ShowDialog() method.
ColorDialog dlg = new ColorDialog();
dlg.ShowDialog();
The following C# program invites a color dialog box and retrieve the selected color to a
string.
using System;
{
{
public Form1()
{
}
{
ColorDialog dlg = new ColorDialog();
dlg.ShowDialog();
if (dlg.ShowDialog() == DialogResult.OK)
{
string str = null;
str = dlg.Color.Name;
MessageBox.Show (str);
}
}
}
}
C# Font Dialog Box
Font dialog box represents a common dialog box that displays a list of fonts that are
currently installed on the system. The Font dialog box lets the user choose attributes for
a logical font, such as font family and associated font style, point size, effects , and a
script.

87
using System;
{
{
public Form1()
{
}
{
FontDialog dlg = new FontDialog();
dlg.ShowDialog();
{
string fontName;
float fontSize;
fontName = dlg.Font.Name;
fontSize = dlg.Font.Size;
MessageBox.Show(fontName + " " + fontSize );
}
}
}
}

88
C# OpenFile Dialog Box
The OpenFileDialog component allows users to browse the folders of their computer or
any computer on the network and select one or more files to open. The dialog box
returns the path and name of the file the user selected in the dialog box.
The FileName property can be set prior to showing the dialog box. This causes the
dialog box to initially display the given filename. In most cases, your applications
should set the InitialDirectory, Filter, and FilterIndex properties prior to calling
ShowDialog.
The following C# program invites an OpenFile Dialog Box and retrieve the selected
filename to a string.
using System;
{
{
public Form1()
{
}
{
OpenFileDialog dlg = new OpenFileDialog();
dlg.ShowDialog();

89
{
string fileName;
fileName = dlg.FileName;
MessageBox.Show(fileName);
}
}
}
}
C# Print Dialog Box
A user can use the Print dialog box to select a printer, configure it, and perform a print
job. Print dialog boxes provide an easy way to implement Print and Print Setup dialog
boxes in a manner consistent with Windows standards.
The Print dialog box includes a Print Range group of radio buttons that indicate whether
the user wants to print all pages, a range of pages, or only the selected text. The dialog
box includes an edit control in which the user can type the number of copies to print. By
default, the Print dialog box initially displays information about the current default
printer.
using System;
namespace Win
dowsFormsApplication1
{
{
public Form1()
{

90
}
{
PrintDialog dlg = new PrintDialog();
dlg.ShowDialog();
}
}
}
C# Label Control
Labels are one of the most frequently used C# control. We can use the Label control to
display text in a set location on the page. Label controls can also be used to add
descriptive text to a Form to provide the user with helpful information. The Label class
is defined in the System.Windows.Forms namespace.
Add a Label control to the form - Click Label in the Toolbox and drag it over the forms
Designer and drop it in the desired location.
If you want to change the display text of the Label, you have to set a new text to the
Text property of Label.
label1.Text = "This is my first Label";
In addition to displaying text, the Label control can also display an image using the
Image property, or a combination of the ImageIndex and ImageList properties.
label1.Image = Image.FromFile("C:testimage.jpg");
using System;
{
{
public Form1()
{
}

91
{
label1.Text = "This is my first Lable";
label1.BorderStyle = BorderStyle.FixedSingle;
label1.TextAlign = ContentAlignment.MiddleCenter;
}
}
}
C# Button Control
Windows Forms controls are reusable components that encapsulate user interface
functionality and are used in client side Windows applications. A button is a control,
which is an interactive component that enables users to communicate with an
application. The Button class inherits directly from the ButtonBase class. A Button can
be clicked by using the mouse, ENTER key, or SPACEBAR if the button has focus.
When you want to change display text of the Button , you can change the Text property
of the button.
button1.Text = "Click Here";
Similarly if you want to load an Image to a Button control , you can code like this
button1.Image = Image.FromFile("C:testimage.jpg");
How to Call a Button's Click Event Programmatically
The Click event is raised when the Button control is clicked. This event is commonly
used when no command name is associated with the Button control. Raising an event
invokes the event handler through a delegate.
{
Button b = new Button();
b.Click += new EventHandler(ShowMessage);
Controls.Add(b);
}
private void ShowMessage(object sender, EventArgs e)
{
MessageBox.Show("Button Click");
}

92
C# MDI Form
A Multiple Document Interface (MDI) programs can display multiple child windows
inside them. This is in contrast to single document interface (SDI) applications, which
can manipulate only one document at a time. Visual Studio Environment is an example
of Multiple Document Interface (MDI) and notepad is an example of an SDI application.
MDI applications often have a Window menu item with submenus for switching
between windows or documents.
Any windows can become an MDI parent, if you set the IsMdiContainer property to
True.
IsMdiContainer = true;
The following C# program shows a MDI form with two child forms. Create a new C#
project, then you will get a default form Form1 . Then add two mnore forms in the
project (Form2 , Form 3) . Create a Menu on your form and call these two forms on
menu click event.
NOTE: If you want the MDI parent to auto-size the child form you can code like this.

93
form.MdiParent = this;
form.Dock=DockStyle.Fill;
form.Show();
using System;
{
{
public Form1()
{
}
{
IsMdiContainer = true;
}
{
Form2 frm2 = new Form2();
frm2.Show();
frm2.MdiParent = this;
}
{
Form3 frm3 = new Form3();
frm3.Show();
frm3.MdiParent = this;
}
}
}
keyPress event in C#
Handle Keyboard Input at the Form Level in C#
Windows Forms processes keyboard input by raising keyboard events in response to
Windows messages. Most Windows Forms applications process keyboard input
exclusively by handling the keyboard events.
How do I detect keys pressed in C#
You can detect most physical key presses by handling the KeyDown or KeyUp events.
Key events occur in the following order:

94
KeyDown
KeyPress
KeyUp
How to detect when the Enter Key Pressed in C#
The following C# code behind creates the KeyDown event handler. If the key that is
pressed is the Enter key, a MessegeBox will displayed .
{
MessageBox.Show("Enter Key Pressed ");
}
How to get TextBox1_KeyDown event in your C# source file ?
Select your TextBox control on your Form and go to Properties window. Select Event
icon on the properties window and scroll down and find the KeyDown event from the
list and double click the Keydown Event. The you will get the KeyDown event in your
source code editor.
private void textBox1_KeyDown(.....)
{
}

95
Difference between the KeyDown Event, KeyPress Event and KeyUp Event
KeyDown Event : This event raised as soon as the user presses a key on the keyboard,
it repeats while the user keeps the key depressed.
KeyPress Event : This event is raised for character keys while the key is pressed and
then released. This event is not raised by noncharacter keys, unlike KeyDown and
KeyUp, which are also raised for noncharacter keys
KeyUp Event : This event is raised after the user releases a key on the keyboard.
KeyPress Event :
using System;
{
{
public Form1()
{
}
private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.Enter)
{
MessageBox.Show("Enter key pressed");
}
if (e.KeyChar == 13)
{
}
}
}
}
KeyDown Event :
using System;
{
{
public Form1()
{
}
private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
{

96
}
}
}
}
How to Detecting arrow keys in C#
In order to capture keystrokes in a Forms control, you must derive a new class that is
based on the class of the control that you want, and you override the ProcessCmdKey().
KeyUp Event :
The following C# source code shows how to capture Enter KeyDown event from a
TextBox Control.
using System;
{
{
public Form1()
{
}
private void textBox1_KeyUp(object sender, KeyEventArgs e)
{
{
}
}
}
}
How to create Dynamic Controls in C# ?
How to create Control Arrays in C# ?
Visual Studio .NET does not have control arrays like Visual Basic 6.0 does. The good
news is that you can still set things up to do similar things. The advantages of C#
dynamic controls is that they can be created in response to how the user interacts with
the application. Common controls that are added during run-time are the Button and
TextBox controls. But of course, nearly every C# control can be created dynamically.

97
How to create Dynamic Controls in C# ?
The following program shows how to create a dynamic TextBox control in C# and
setting the properties dynamically for each TextBox control. Drag a Button control in
the form and copy and paste the following source code.
using System;
{
{
int cLeft = 1;
public Form1()
{
}
{
AddNewTextBox();
}
public System.Windows.Forms.TextBox AddNewTextBox()
{
System.Windows.Forms.TextBox txt = new System.Windows.Forms.TextBox();
this.Controls.Add(txt);
txt.Top = cLeft * 25;
txt.Left = 100;
txt.Text = "TextBox " + this.cLeft.ToString();
cLeft = cLeft + 1;
return txt;
}
}
}

98
Keep Form on Top of All Other Windows
The System.Windows.Forms namespace contains classes for creating Windows-based
applications that take full advantage of the rich user interface features available in the
Microsoft Windows operating system. You can bring a Form on top of application by
simply setting the Form.topmost form property to true will force the form to the top
layer of the screen, while leaving the user able to enter data in the forms below.
Form2 frm = new Form2();
frm.TopMost = true;
frm.Show();
Topmost forms are always displayed at the highest point in the z-order of the windows
on the desktop. You can use this property to create a form that is always displayed in
your application, such as a MessageBox window.
using System;
{
{
public Form1()
{
}
{
Form2 frm = new Form2();
frm.TopMost = true;
frm.Show();
}
}
}

99
C# Timer Control
What is Timer Control ?
The Timer Control plays an important role in the development of programs both Client
side and Server side development as well as in Windows Services. With the Timer
Control we can raise events at a specific interval of time without the interaction of
another thread.
Use of Timer Control
We require Timer Object in many situations on our development environment. We have
to use Timer Object when we want to set an interval between events, periodic checking,
to start a process at a fixed time schedule, to increase or decrease the speed in an
animation graphics with time schedule etc.
A Timer control does not have a visual representation and works as a component in the
background.
How to Timer Control ?
We can control programs with Timer Control in millisecond, seconds, minutes and even
in hours. The Timer Control allows us to set Intervel property in milliseconds. That is,
one second is equal to 1000 milliseconds. For example, if we want to set an interval of 1
minute we set the value at Interval property as 60000, means 60x1000 .
By default the Enabled property of Timer Control is False. So before running the
program we have to set the Enabled property is True , then only the Timer Control starts
its function.

100
In the following program we display the current time in a Label Control. In order to
develop this program, we need a Timer Control and a Label Control. Here we set the
timer interval as 1000 milliseconds, that means one second, for displaying current
system time in Label control for the interval of one second.
using System;
{
{
public Form1()
{
}
private void timer1_Tick(object sender, EventArgs e)
{
label1.Text = DateTime.Now.ToString();
}
}
}
Start and Stop Timer Control
The Timer control have included the Start and Stop methods for start and stop the Timer
control functions.
Here we run this program only 10 seconds. In order to doing this ,in the following
program we set Timer interval as 1000 (1 second) and check each seconds for stopping
the Timer Control after 10 seconds.

101
Code
using System;
{
{
int second = 0;
public Form1()
{
}
{
timer1.Interval = 1000;
timer1.Start();
}
private void timer1_Tick(object sender, EventArgs e)
{
label1.Text = DateTime.Now.ToString();
second = second + 1;
if (second >= 10)
{
timer1.Stop();
MessageBox.Show("Exiting from Timer....");
}
}
}
}

102
Object Oriented Programming
Structured programming is not the wrong way to write programs. Similarly, object-oriented
programming is not necessarily the right way. Object-oriented programming (OOP) is an
alternative program development technique that often tends to be better if we deal with large
programs and if we care about program reusability.
We make the following observations about structured programming:
- Structured programming is narrowly oriented towards solving one particular
problem
- It would be nice if our programming efforts could be oriented more broadly
- Structured programming is carried out by gradual decomposition of the functionality
- The structures formed by functionality/actions/control are not the most stable parts
of a program
- Focusing on data structures instead of control structure is an alternative approach
- Real systems have no single top - Real systems may have multiple tops [Bertrand
Meyer]
- It may therefore be natural to consider alternatives to the top-down approach
OOP Concepts
1. Data Abstraction – it is the act of representing the essential features without
including the background details. Data Hiding- it is a related concept of data abstraction.
Unessential features are hidden from the world.
2. Data Encapsulation – it is the wrapping of data and associated functions in one single unit.
3. Inheritance – it is the capability of one class to inherit properties from other class.
4. Polymorphism – it is the ability for data to be processed in more than one form.
5. Modularity – it is the concept of breaking down the program into several module. E.g. :
Classes, Structure, etc.

103
Class
Class: is an abstraction model used to define a new Data Type Which May Contain a Combination
of encapsulating Data (Member Variable) Operation That Can Be Perform On Data (Member
Function) And Accessory to Data (properties).
Member Variable = Field
Member Function = Method
Properties = Attributes
Declaration
Class Class_name
{
[Properties] Member Variable;
[Properties] Member Function;
.
.
.
}
Class_name var = new Class_name ();
❖ Class can declared before or after main method
❖ Or can be declared before class program.
❖ we can change class program to any name
What a class is
Classes are the user defined data types that represent the state and behaviour of an object. State
represents the properties and behaviour is the action that objects can perform.
Classes can be declared using the following access specifiers that limit the accessibility of classes
to other classes, however some classes does not require any access modifiers.
1. Public
2. Private
3. Protected
4. Internal
5. Protected internal
To learn the details of access specifiers please refer to the following article of mine:
• Access Modifiers in C#

104
For example:
public class Accounts
{
}
Some Key points about classes
• Classes are reference types that hold the object created dynamically in a heap.
• All classes have a base type of System.Object.
• The default access modifier of a class is Internal.
• The default access modifier of methods and variables is Private.
• Directly inside the namespaces declarations of private classes are not allowed.
The following are types of classes in C#:
What an Abstract class is
An Abstract class is a class that provides a common definition to the subclasses and this is the type
of class whose object is not created.
Some key points of Abstract classes are:
• Abstract classes are declared using the abstract keyword.
• We cannot create an object of an abstract class.
• If you want to use it then it must be inherited in a subclass.
• An Abstract class contains both abstract and non-abstract methods.
• The methods inside the abstract class can either have an implementation or no
implementation.
• We can inherit two abstract classes; in this case the base class method implementation is
optional.
• An Abstract class has only one subclass.
• Methods inside the abstract class cannot be private.
• If there is at least one method abstract in a class then the class must be abstract.
For example:
abstract class Accounts
{
}

105
Partial Classes
It is a type of class that allows dividing their properties, methods and events into multiple source
files and at compile time these files are combined into a single class.
The following are some key points:
• All the parts of the partial class must be prefixed with the partial keyword.
• If you seal a specific part of a partial class then the entire class is sealed, the same as for an
abstract class.
• Inheritance cannot be applied on partial classes.
• The classes that are written in two class files are combined together at run time.
For example:
partial class Accounts
{
}
Sealed Class
A Sealed class is a class that cannot be inherited and used to restrict the properties.
• A Sealed class is created using the sealed keyword.
• Access modifiers are not applied to a sealed class.
• To access the sealed members we must create an object of the class.
For example:
sealed class Accounts
{
}
Static Class
It is the type of class that cannot be instantiated, in oher words we cannot create an object of that
class using the new keyword, such that class members can be called directly using their class name.
• Created using the static keyword.
• Inside a static class only static members are allowed, in other words everything inside
thestatic class must be static.
• We cannot create an object of the static class.
• A Static class cannot be inherited.
• It allows only a static constructor to be declared.

106
• The methods of the static class can be called using the class name without creating the
instance.
For example:
static class Accounts
{
}
// Example 1
// Define Class point
class coordinate
{
public int x;
public int y;
public void setx(int a)
{ x = a; }
public void sety(int b)
{ y = b; }
public int getx()
{ return (x); }
public int gety()
{ return (y); }
}
// Calling the Class
{
coordinate p = new coordinate();
p.x = 10;
p.y = 5;
p.setx(6);
p.sety(7);
textBox1.Text = Convert.ToString(p.getx());
textBox2.Text = Convert.ToString(p.gety());
}
//Example 2
// Define Class circle
class circle
{
double radius;
double pi = 3.141;
public double area()
{ return (radius * radius * pi); }
public void set_r(double b)

107
{ radius = b; }
}
{
circle c = new circle();
double x = Convert.ToDouble(textBox1.Text);
c.set_r(x);
textBox2.Text=Convert.ToString( c.area());
}
//Example 3
// Class array Define and Sort
class sort
{
int[] ar = new int[10];
public void set_array(int[] a)
{ ar = a; }
public int[] get_array()
{ Array.Sort(ar); return ((ar)); }
}
{
sort s = new sort();
int[] b = new int[10] { 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 };
s.set_array(b);
b=s.get_array();
for (int i = 0; i < 10; i++)
{ textBox1.Text = textBox1.Text + b[i]; }
}
Multi-Function in Class
//Example 4
//Class
class stage2
{ double fp = 1;
public double factx(int x)
{ for (int i = x; i > 0; i--)
{ fp = fp * i; }
return(fp); }
public double powx(int x,int y)

108
{ fp = Math.Pow(x, y);
return (fp); }
public string str_up(string a)
{return (a.ToUpper());}
public string str_dn(string a)
{return(a.ToLower());}
public string get_s;
public string set_s;
public void find_array(string[,] s)
{ for (int j = 0; j < 10; j++)
if (get_s == s[0, j])
{ set_s =s[2,j]+":"+s[0,j]+" = "+ s[1, j]; break; }
}
}
// Calling the Class from Button
{
string[,] st = new string[3, 10] { { "AA", "AB", "AC", "AD", “……..
stage2 s2 = new stage2();
if (comboBox1.Text == "factorial")
{ int x = Convert.ToInt32(textBox1.Text);
textBox2.Text = Convert.ToString(s2.factx(x));
}
else if (comboBox1.Text == "power")
{
int x = Convert.ToInt32(textBox1.Text);
textBox2.Text = Convert.ToString(s2.powx(x, x));
}
else if (comboBox1.Text == "upper")
{
string s = textBox1.Text;
textBox2.Text = s2.str_up(s);
}
else if (comboBox1.Text == "lower")
{
string s = textBox1.Text;
textBox2.Text = s2.str_dn(s);
}
else if (comboBox1.Text == "find")
{ s2.get_s = textBox3.Text;
s2.find_array(st);
textBox4.Text = s2.set_s;
} }

109
Constructor
Constructor: Is a special method used when an object of class is created, and is called automatically
in order to initialize a new instance of a class
Constructor properties
‽ Constructor has the same name of the class.
‽ Constructor does not return value.
‽ Constructor can be overloaded.
‽ Constructor has public access.
➢ Default Construction: has no parameters list.
➢ Parameter Construction: has parameters list.
➢ Copy Construction: has object parameter type.
//Example 5
//Class
class pickup
{ string model;
double speed;
public pickup() // Default Construction
{ model = ""; speed = 0; }
public pickup(string s, double d) // Parameter Construction
{ model = s; speed = d; }
public pickup(pickup k) // Copy Construction
{ model = k.model; speed = k.speed; } }
//Button
{ pickup c1 = new pickup(); // Default Construction
pickup c2 = new pickup("toyota", 220); // Parameter Construction
pickup c3 = new pickup(c2); // Copy Construction
}
Copy constructors: can be used for making copies of existing objects. A copy constructor can
be recognized by the fact that it takes a parameter of the same type as the class to which it belongs.
Object copying is an intricate matter, because we will have to decide if the referred object should
be copied too (shallow copying, deep copying, or something in between,

110
Destructor
Since C# is garbage collected, meaning that the framework will free the objects that you no longer
use, there may be times where you need to do some manual cleanup. A destructor, a method called
once an object is disposed, can be used to cleanup resources used by the object. Destructor doesn't
look very much like other methods in C#. Here is an example of a destructor for our Car class:
➢ Is a method called once an object is disposed, can be used to cleanup recourse used by the
object.
➢ Destructors only used with classes.
➢ A class can only have one destructor.
➢ Destructor cannot be inherited or overloaded.
➢ Destructor cannot be called, They are invoked automatically.
➢ Destructors cannot take a modifiers or have parameters.
~rain ()
{
MessageBox.Show("car object is dead");
}
//Example 6
//Class
class company
{ string model;
double speed;
public company() // Default Construction
{ model = ""; speed = 0; }
public company(string s, double d) // Parameter Construction
{ model = s; speed = d; }
public company(company k) // Copy Construction
{ model = k.model; speed = k.speed; }
public ~ company() // Destructor
{MessageBox.Show(" Destructor "); }
}
//Button
{ company c1 = new company(); // Default Construction
company c2 = new company("toyota", 220); // Parameter Construction
company c3 = new company(c2); // Copy Construction
}

111
Accessibility Keywords
All types and type members have an accessibility level, which controls whether they can be used
from other code in your assembly or other assemblies. You can use the following access modifiers
to specify the accessibility of a type or member when you declare it:
1. Public: The type or member can be accessed by any other code in the same assembly or
another assembly that references it.
2. Private: The type or member can be accessed only by code in the same class or structure.
3. Protected: The type or member can be accessed only by code in the same class or structure,
or in a class that is derived from that class.
4. Internal: The type or member can be accessed by any code in the same assembly, but not
from another assembly.
Public
The public keyword is an access modifier for types and type members. Public access is the most
permissive access level.
There are no restrictions on accessing public members.
Accessibility:
1. Can be accessed by objects of the class
2. Can be accessed by derived classes
Note: In the following example num1 is direct access.
//Example 7
//Class
class Program
{
class AccessMod
{
public int num1;
int num2;
}
//Button
{ AccessMod ob1 = new AccessMod();

112
//Direct access to public members
ob1.num1 = 100;
//Access to private member is not permitted
ob1.num2 = 20;
MessageBox.Show("Number one value in main {0}", ob1.num1);
}
The above program will give compilation error, as access to private is not permissible. In the below
figure you can see the private member num2 is not available.
Private
Private access is the least permissive access level.
Private members are accessible only within the body of the class or the structure in which they are
declared.
Accessibility:
1. Cannot be accessed by object
2. Cannot be accessed by derived classes
Note: In the following example num2 is not accessible outside the class.
//Example 8
//Class
class Program
{ class AccessMod
{ public int num1;
int num2; }
{ AccessMod ob1 = new AccessMod();
//Direct access to public members
ob1.num1 = 100;
//Access to private member is not permitted
ob1.num2 = 20;
MessageBox.Show("Number one value in main {0}", ob1.num1);
}

113
The above program will give compilation error, as access to private is not permissible. In the
below figure you can see the private member num2 is not available.
Protected
A protected member is accessible from within the class in which it is declared, and from within any
class derived from the class that declared this member.
A protected member of a base class is accessible in a derived class only if the access takes place
through the derived class type.
Accessibility:
Cannot be accessed by object By derived classes
//Example 9
class Base
{ protected int num1; }
class Derived : Base
{ public int num2; }
{
Base ob1 = new Base();
Derived ob2 = new Derived();
ob2.num1 = 20;
// Access to protected member as it is inherited by the Derived class
ob2.num2 = 90;
}
In the above program we try to access protected member in main it is not available as shown in the
picture below that num1 is not listed.
Parent Class Access Modifier Access in child Class
Public Accessible
Private Accessible
Protected Not Accessible

114
Inheritance
 Inheritance allows a software developer to derive a new class from an existing one.
 The existing class is called the parent, super, or base class.
 The derived class is called a child or subclass.
 The child inherits characteristics of the parent.
o Methods and data defined for the parent class.
 The child has special rights to the parent's methods and data.
o Public access like anyone else
o Protected access available only to child classes.
 The child has its own unique behaviors and data.
i. Inheritance relationships are often shown graphically in a class diagram, with the arrow
pointing to the parent class.
ii. Inheritance should create a relationship, meaning the child is a more specific version of the
parent.
Declaring a Derived Class
Define a new class DerivedClass which extends BaseClass
class BaseClass
{
// class contents
}

115
class DerivedClass : BaseClass
{
// class contents
}
Controlling Inheritance
❖ A child class inherits the methods and data defined for the parent class; however, whether a
data or method member of a parent class is accessible in the child class depends on the
visibility modifier of a member.
❖ Variables and methods declared with private visibility are not accessible in the child class
o However, a private data member defined in the parent class is still part of the state of
a derived class.
❖ Variables and methods declared with public visibility are accessible; but public variables
violate our goal of encapsulation
❖ There is a third visibility modifier that helps in inheritance situations: protected.
//Example A
//Class
class color //Class name
{
public color() //Constructor
{
MessageBox.Show("color");
}
public void fill(string s) //function
{
(Messagebox.Show(s);
}
}
class green : color //green class child of parent " color" ' inheritance'
{
public green() //constructor
{
MessageBox.Show ("green");
}
}
// Call them through button
{ green g = new green();
g.fill("red"); }
//Example B
//Class
class animal
{
public animal()
{

116
MessageBox.Show("animal");
}
public void talk()
{
MessageBox.Show("animal talk");
}
public void greet()
{
MessageBox.Show("animal say hello");
}
}
class dog : animal
{
public dog()
{
MessageBox.Show("dog");
}
public void sing()
{
MessageBox.Show("dog can sing");
}
}
//Button
{ animal a = new animal();
a.talk();
a.greet();
dog d = new dog();
d.sing();
d.talk();
d.greet();
}
Notes about Inheritance:
➢ Constructor can't be inheritance, they just invoked.
➢ First call base then derived.
➢ Destructor can't be inheritance they just invoked.
➢ First call derived then base.
Inheritance with Constructor and Destructor
class animal
{
public animal() //Constructor
{
MessageBox.Show("animal");
}
public void talk() //Function

117
{
MessageBox.Show("animal talk");
}
public void greet() //Function
{
MessageBox.Show("animal say hello");
}
~animal() //Destructor
{
MessageBox.Show("animal Destructor");
}
}
class dog : animal
{
public dog() //Constructor
{
MessageBox.Show("dog");
}
public void sing() //Function
{
MessageBox.Show("dog can sing");
}
~dog() //Destructor
{
MessageBox.Show("dog Destructor");
}
}
{ animal a = new animal();
a.talk();
a.greet();
dog d = new dog();
d.sing();
d.talk();
d.greet();
}

118
Base Classes and Derived Classes
Single Inheritance
▪ Some languages, e.g., C++, allow Multiple inheritance, which allows a class to be derived
from two or more classes, inheriting the members of all parents.
▪ C# and Java support single inheritance, meaning that a derived class can have only one
parent class.
Base class Derived classes
Student GraduateStudent
UndergraduateStudent
Shape Circle
Triangle
Rectangle
Loan CarLoan
HomeImprovementLoan
MortgageLoan
Employee FacultyMember
StaffMember
Account CheckingAccount
SavingsAccount

119
Hierarchical inheritance
Multilevel inheritance
Single inheritance
Multiple inheritances

120
▪ An inherited member is continually passed down the line
▪ Inheritance is transitive.
▪ Good class design puts all common features as high in the hierarchy as is
reasonable. Avoids redundant code.
References and Inheritance
▪ An object reference can refer to an object of its class, or to an object of any
class derived from it by inheritance.
▪ For example, if the Holiday class is used to derive a child class called Friday,
then a Holiday reference can be used to point to a Fridayobject.
Class_Name1 object_name;
object_name=new Class_Name1();
object_name=new Class_Name2();
Polymorphism
The word polymorphism means having many forms. In object-oriented programming paradigm,
polymorphism is often expressed as 'one interface, multiple functions'.
Polymorphism can be static or dynamic. In static polymorphism, the response to a function is
determined at the compile time. In dynamic polymorphism, it is decided at run-time.
StaticPolymorphism
The mechanism of linking a function with an object during compile time is called early binding. It
is also called static binding. C# provides two techniques to implement static polymorphism. They
are:
• Function overloading
• Operator overloading
We discuss operator overloading in next chapter.
FunctionOverloading
You can have multiple definitions for the same function name in the same scope. The definition of
the function must differ from each other by the types and/or the number of arguments in the
argument list. You cannot overload function declarations that differ only by return type.

121
The following example shows using function print() to print different data types:
using System;
namespace PolymorphismApplication
{
class Printdata
{
void print(int i)
{
MessageBox.Show("Printing int: {0}", i );
}
void print(double f)
{
MessageBox.Show("Printing float: {0}" , f);
}
void print(string s)
{
MessageBox.Show("Printing string: {0}", s);
}
{
Printdata p = new Printdata();
// Call print to print integer
p.print(5);
// Call print to print float
p.print(500.263);
// Call print to print string
p.print("Hello C++");
}
}
}

122
DynamicPolymorphism
C# allows you to create abstract classes that are used to provide partial class implementation of an
interface. Implementation is completed when a derived class inherits from it. Abstract classes
contain abstract methods, which are implemented by the derived class. The derived classes have
more specialized functionality.
Here are the rules about abstract classes:
• You cannot create an instance of an abstract class
• You cannot declare an abstract method outside an abstract class
• When a class is declared sealed, it cannot be inherited, abstract classes cannot be declared
sealed.
The following program demonstrates an abstract class:
using System;
{
abstract class Shape
{
public abstract int area();
}
class Rectangle: Shape
{
private int length;
private int width;
public Rectangle( int a=0, int b=0)
{
length = a;
width = b;
}
public override int area ()
{
MessageBox.Show("Rectangle class area :");
return (width * length);
}

123
}
class RectangleTester
{
{
Rectangle r = new Rectangle(10, 7);
double a = r.area();
MessageBox.Show("Area: {0}",a);
}
}
}
When you have a function defined in a class that you want to be implemented in an inherited
class(es), you use virtual functions. The virtual functions could be implemented differently in
different inherited class and the call to these functions will be decided at runtime.
Dynamic polymorphism is implemented by abstract classes and virtual functions.
The following program demonstrates this:
using System;
{
class Shape
{
protected int width, height;
public Shape( int a=0, int b=0)
{
width = a;
height = b;
}
public virtual int area()
{
MessageBox.Show("Parent class area :");
return 0;

124
}
}
class Rectangle: Shape
{
public Rectangle( int a=0, int b=0): base(a, b)
{
}
public override int area ()
{
MessageBox.Show("Rectangle class area :");
return (width * height);
}
}
class Triangle: Shape
{
public Triangle(int a = 0, int b = 0): base(a, b)
{
}
public override int area()
{
MessageBox.Show("Triangle class area :");
return (width * height / 2);
}
}
class Caller
{
public void CallArea(Shape sh)
{
int a;
a = sh.area();
MessageBox.Show("Area: {0}", a);
}
}

125
class Tester
{
{
Caller c = new Caller();
Rectangle r = new Rectangle(10, 7);
Triangle t = new Triangle(10, 5);
c.CallArea(r);
c.CallArea(t);
}
}
}
Overriding
✓ A child class can override the definition of an inherited method in favor of its own
✓ That is, a child can redefine a method that it inherits from its parent
✓ The new method must have the same signature as the parent's method, but can have a
different implementation.
✓ The type of the object executing the method determines which version of the method is
invoked.
Overriding Methods
➢ C# requires that all class definitions communicate clearly their intentions.
➢ The keywords virtual, override and new provide this communication.
➢ If a base class method is going to be overridden it should be declared virtual.
➢ A derived class would then indicate that it indeed does override the method with the
override keyword.
➢ If a derived class wishes to hide a method in the parent class, it will use the new keyword.
This should be avoided.

126
Overloading vs. Overriding
❖ Overloading deals with multiple methods
in the same class with the same name but
different signatures
❖ Overloading lets you define a similar
operation in different ways for different
data
Example:
int ovr(string[ ] bar);
int ovr(int bar1, float a);
❖ Overriding deals with two methods, one in
a parent class and one in a child class, that
have the same signature
❖ Overriding lets you define a similar
operation in different ways for different
object types
Example:
class Base {
public virtual int ovrid()
{ }
}
class Derived {
public override int ovrid() {
} }
public class Base
{
public virtual void Show()
{
MessageBox.Show("Show From Base Class.");
}
}
public class Derived : Base
{
public override void Show()
{
MessageBox.Show("Show From Derived Class.");
}
}
Overloading (Compile Time Polymorphism):: Functions with same name and different parameters.
public class A
{
public void print(int x, int y)
{
Console.WriteLine("Parent Method");
}
}
public class B : A
{

127
public void child()
{
Console.WriteLine("Child Method");
}
public void print(float x, float y)
{
Console.WriteLine("Overload child method");
}
}
Overriding (Run Time Polymorphism):: Functions in the extended class with same name and same
parameters as in the base class, but with different behaviors.
public class A
{
public virtual void print()
{
Console.WriteLine("Parent Method");
}
}
public class B : A
{
public void child()
{
Console.WriteLine("Child Method");
}
public override void print()
{
Console.WriteLine("Overriding child method");
}
}
The End

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