c sharp (first slide)

8/8/2019 C Sharp (First Slide)

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C# - In the beginning



The Hello,World! C# Program

//Example2-1.cs

//The first program in C#

Class HelloWorld

{static void Main()

{

System.Console.WriteLine("Hello,World!");

}

}



//Example2-2.cs

//The second program in C#

usingSystem;

Class HelloWorld{

static void Main()

{

Console.WriteLine("Hello,World!");}

}



Using Local Variable

//Example2-3.cs

//Local variables.

Using System;

Class MyClass

{

static void Main()

{

string myString = "Hello,World!";

Console.WriteLine("The string is:"+myString);}

}



The Program Architecture

A C# program may contain one or more files.

Any file can contain any of the following elements:

Directives

Namespaces(which can contain all other elements andnamespaces)

Classes

Structs(structures)

Interfaces

Delegates Enums(enumerations)

Function members(such as methods, properties, indexers,and so forth)



DataTypes

In C#, there are two types

Value types: Variables that stored at a

values on the stack. Reference types: Variables that store

memory addresses of the data stored on

the heap.



Built in Data Types

bool

byte

sbyte char

decimal

double float

int

uint

long

ulong object

short

ushort string



Value Types

Value types include the numeric types

(integers, floats, and so forth) and the Boolean

type (bool).

They also include user-defined types such as

structs and enumerations.

Bool - byte - char decimal double enum

Float int long sbyte - struct - uint

ulong ushort



Variable Initialization

intmyValue=123; intmyValue=0;

intmyValue=newint();

Struct :structPoint

{

intx;

inty;

}

Point myPoint=newPoint();



Reference Types

A reference-type variable does not contain thedata itself;

It actually contains the memory address of the

data.

The following are the C# reference types:

± Class

± Interface

± Delegate

± Object

± String



Boxing and Unboxing

The boxing operation is accomplished by

assigning the value-type variable to a variable

of the type object:

± Int myInt = 123;

± Object myObj = myInt; //boxing

This means moving the value 123 from the

stack to the heap.



Unboxing

In order to convert the variable back to a

value type you use the unboxing operation,

which is performed by casting the reference-

type variable with (int).

The following statement assigns the value

pointed to by myObj to a new value-type

variable, yourInt:

yourInt=(int)myObj; //unboxing



Operators

Arithmetic : + , , * , /

Modulo : %

Compound Assignment : *= x*=y; x=x*y;

/= x/=y; x=x/y;

%= x%=y; x=x%y; += x+=y; x=x+y;

= x=y; x=xy;



Increment and decrement operators are

classified as unary or primary arithmetic

operators.

x++; // increase the value of x by one

y--; // decrease the value of y by one

--y+x //means decrement y before adding its

value to x. (prefix)

y--+x //means decrement y after adding its

value to x. (suffix)

An Example : Increment and Decrement



Formatting Results

Currency

± Console.WriteLine("{0:C}",1.2);

±Output = $1.20

If the number 1.2 is negative, like this:

± Console.WriteLine("{0:C}",-1.2);

± It appears inside parentheses like this: ($1.20).



The Decimal Format

To display a number preceded by a specified

number of zeroes, use the format character

D or d, like this example:

± Console.WriteLine("{0:D5}",123);

The result of this statement is 00123.

The number following the letterD

determines the number of decimal places in

the output.



The Fixed-point Format

To display a number followed by a specified

number of decimal places, use Forf, like

these examples.

The output of each statement is written next

to it as a comment.

± Console.WriteLine("{0:F2}",12);

//12.00 two decimal places

± Console.WriteLine("{0:F0}",12);

//12 no decimal places



The General Format To display a number in the default format, use

the letterGorglike this: ± Console.WriteLine("{0:G}",1.2);//1.2

± Console.WriteLine("{0:G}",1.23);//1.23

As you can see in the comments that followthe statements, this is the same output

produced by no formatting at all.

The statements are then equivalent to thesestatements:

± Console.WriteLine("{0}",1.2);

± Console.WriteLine("{0}",1.23);



There are scientific format and hexadecimal

formats.

Do the following example for formats and youcan understand how C# handles them

Example : Number Formats



The stringType

String myString;

String myString="Welcome to the string

world!"; String myString="My friend, \nWelcome to

the string world!";



String Operators

To concatenate two strings, use the + operator

as in this example:

± String myString="Hello"+","+"World!";

You can also concatenate string variables.

First declare and initialize the variables:

± String hello="Hello";

String world="World!";



Reading the Keyboard Input

To read input from the keyboard, use the .NET

method ReadLine.

Ex : string myString=Console.ReadLine();

Example : Keyboard input



Converting Strings to Numbers

Long myLong = Convert.ToInt64(myString);//convert to long

Float myFloat = Convert.ToSingle(myString);//convert to float

Double myDouble =Convert.ToDouble(myString); //convert to double

Decimal myDecimal =

Convert.ToDecimal(myString); //convert to decimal

Example : Convert Strings



Using the Parse Method

The second way to convert strings to numbers

is by using the Parse method, one of the .NET methods.

It can be used like this:

Int myInt=Int32.Parse(myString); ± Int64.Parse(myString)//converttolong

± Single.Parse(myString)//converttofloat

± Decimal.Parse(myString)//converttodecimal ± Double.Parse(myString)//converttodouble

Example : Convert using Parse



Relational OperatorsOperator Description

> Greater than

>= Greater than or equal to

< Less than

<= Less than or equal to

== Equal to

!= Not equal to

Example : Relational Operators



Logical Operators

Operator Description

&& AND(Short-circuit evaluation)

|| OR(Short-circuit evaluation)

& AND

| OR

! NOT

Short ± cir cuit evaluation : if one expression is

wrong, none of the following expression will be

evaluated.

Ex: (x>5)&&(y==10)//false



The if-else Construct

if(salary>2000)

{

Console.Write("Salary is greater than 2k"); //The original

result}

Else

{

Console.Write("Salary is less than or equal to 2k"); //TheAlternative result

Example : IfElse



The switch Construct

Example : Switch Construct

The Conditional Expression The conditional expression is used to build a

simple conditional statement. condition ? expression_1 : expression_2

condition is the Boolean expression to test.

Which return True or False by evaluatingexpression1 and 2.

Example : ConditionalExpression



Using Libraries DLL

//Example4-5a.cs//Compile as DLL.

Public class Class1

{public static long Factorial(long i)

{

return((i<=1)?1:(i* Factorial(i-1)));}

}



Use the DLL//Example4-5b.cs

Using System;Public class MyClass

{

static void Main()

{Console.Write("Please enter an integer:");

longn=Convert.ToInt64(Console.ReadLine());

Console.WriteLine(Class1.Factorial(n)); //calling the method

}

}



A First Look at the C# Code//EmployeeDLL.cs a class file

Public class Employee

{

//Fields:

public string name;

public string id;

//Methods:

public double CalculateSalary(int hoursWorked,double rate)

{

double salary;

salary=rate* hoursWorked;

return salary;

}

}



Lets use this class file

//MyProgram.cs

usingSystem;

Class MyClass

{

static void Main()

{Employee emp=new Employee();

emp.name=JohnMartinSmith;

emp.id=ABC123";

double weeklyPayment=emp.CalculateSalary(40,55);

emp.CalculateSalary(40,55)

Console.WriteLine(ID:{0},Name:{1},emp.id,emp.name);Console.WriteLine(Payment={0},weeklyPayment);

}

}

Give a link to the cls file



Repetition Loops The For Loop:

± Initialization; condition; increment/decrement;

Class ForLoop

{

static void Main(){

for(int counter=1;counter<=10;counter=counter+2)

{

Console.WriteLine(counter);}

}

}



Using Program Arguments

One possible form of the Main method is:

static void Main(string[]args)

Using this form allows the C# program toaccept as arguments a sequence of strings.

The arguments are received as string array

elements named

args[0],args[1],and so forth.

An Example : Program Arguments



Reversing an Array

In order to reverse an array, use the

statement:

Array.Reverse(myArray); Example : Reverse Array



Namespaces A namespace is a container that includes

classes and other types.

You place the class inside a namespace.

If two classes in two different namespaces

have the same name, you can refer to each

one by using the fully qualified name, for

example :

- MyNameSpace.Class1

- YourNameSpace.Class1

- Example : NameSpaces



Using Properties

Properties expose a convenient public way for

reading and setting field values instead of

dealing directly with the fields.

One advantage of using properties as opposed

to using fields directly is that you can validate

the data before changing the value of the

field.

Example : Property Setting



Read-only Fields

Example : Read Only

Inheritance Example : Inheritance

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