Tutorial 14:Exception Handling

Exceptions are unforeseen errors that happen in your programs. Most of the time, you can, and should, detect and handle program errors in your code. For example, validating user input, checking for null objects, and verifying the values returned from methods are what you expect, are all examples of good standard error handling that you should be doing all the time.
using System;
using System.IO;

class FinallyDemo
{
static void Main(string[] args)
{
FileStream outStream = null;
FileStream inStream = null;

try
{
outStream = File.OpenWrite("DestinationFile.txt");
inStream = File.OpenRead("BogusInputFile.txt");
}
catch(Exception ex)
{
Console.WriteLine(ex.ToString());
}
finally
{
if (outStream != null)
{
outStream.Close();
Console.WriteLine("outStream closed.");
}
if (inStream != null)
{
inStream.Close();
Console.WriteLine("inStream closed.");
}
}
}
}

Tutorial 13:Events

An event is a member that enables an object or class to provide notifications.
As compared to delegates events works with source and listener methodology. So listeners who are interested in receiving some events they subscribe to the source. Once this subscription is done the source raises events to its entire listener when needed. One source can have multiple listeners.
In C# events are based on delegates, with the originator defining one or more call back functions. A call back function is a function in which one piece of code defines another implements, in other words, one piece of code says, “If you implement a function which looks like this, I can call it”. A class that wants to sue events defines callback functions or delegates, and the listening object then implements them.
Events have no return type.
There are following two differences:
1. Events use delegates.
2. Delegates are function pointers they can move across any client.

// File name : events.cs
using System;
namespace CSharp.AStepAhead.events
{
class Button
{
public event EventHandler Click;
public void Reset()
{
Click = null;
}
}
public class impButton
{
Button Button1 = new Button();
public impButton()
{
Button1.Click += new EventHandler(Button1_Click);
}
public void Connect()
{
Console.WriteLine("Attaching the event handler");
Button1.Click += new EventHandler(Button1_Click);
}
void Button1_Click(object s, EventArgs e)
{
Console.WriteLine("Button1 clicked!");
}
public void Disconnect()
{
Console.WriteLine("Removng the event handler");
Button1.Click -= new EventHandler(Button1_Click);
}
static void Main()
{
impButton objButton = new impButton();
objButton.Connect();
Console.ReadLine();
objButton.Disconnect();
Console.ReadLine();
}
}
}

Tutorial 12:Delegates

A delegate is a type-safe object that can point to another method (or possibly multiple methods) in the application, which can be invoked at later time.
when you want to create a delegate in C# you make use of delegate keyword.

The name of your delegate can be whatever you desire. However, you must define the delegate to match the signature of the method it will point to. fo example the following delegate can point to any method taking two integers and returning an integer.

public delegate int DelegateName(int x, int y);

A Delegate Usage Example

namespace MyFirstDelegate
{
//This delegate can point to any method,
//taking two integers and returning an
//integer.
public delegate int MyDelegate(int x, int y);
//This class contains methods that MyDelegate will point to.
public class MyClass
{
public static int Add(int x, int y)
{
return x + y;
}
public static int Multiply(int x, int y)
{
return x * y;
}
}
class Program
{
static void Main(string[] args)
{
//Create an Instance of MyDelegate
//that points to MyClass.Add().
MyDelegate del1 = new MyDelegate(MyClass.Add);
//Invoke Add() method using the delegate.
int addResult = del1(5, 5);
Console.WriteLine("5 + 5 = {0}\n", addResult);
//Create an Instance of MyDelegate
//that points to MyClass.Multiply().
MyDelegate del2 = new MyDelegate(MyClass.Multiply);
//Invoke Multiply() method using the delegate.
int multiplyResult = del2(5, 5);
Console.WriteLine("5 X 5 = {0}", multiplyResult);
Console.ReadLine();
}
}
}
Delegate ability to Multicast
Delegate's ability to multicast means that a delegate object can maintain a list of methods to call, rather than a single method
if you want to add a method to the invocation list of a delegate object , you simply make use of the overloaded += operator, and if you want to remove a method from the invocation list you make use of the overloaded operator -= .
Note: The Multicast delegate here contain methods that return void, if you want to create a multicast delegate with return type you will get the return type of the last method in the invocation list.
A Multicast Delegate Example
namespace MyMulticastDelegate
{
//this delegate will be used to call more than one
//method at once
public delegate void MulticastDelegate(int x, int y);
//This class contains methods that MyDelegate will point to.
public class MyClass
{
public static void Add(int x, int y)
{
Console.WriteLine("You are in Add() Method");
Console.WriteLine("{0} + {1} = {2}\n", x, y, x + y);
}
public static void Multiply(int x, int y)
{
Console.WriteLine("You are in Multiply() Method");
Console.WriteLine("{0} X {1} = {2}", x, y, x * y);
}
}
class Program
{
static void Main(string[] args)
{
//Create an Instance of MulticastDelegate
//that points to MyClass.Add().
MulticastDelegate del = new MulticastDelegate(MyClass.Add);
//using the same instance of MulticastDelegate
//to call MyClass.Multibly() by adding it to it's
//invocation list.
del += new MulticastDelegate(MyClass.Multiply);
//Invoke Add() and Multiply() methods using the delegate.
//Note that these methods must have a void return vlue
Console.WriteLine("****calling Add() and Multibly() Methods.****\n\n");
del(5, 5);
//removing the Add() method from the invocation list
del -= new MulticastDelegate(MyClass.Add);
Console.WriteLine("\n\n****Add() Method removed.****\n\n");
//this will invoke the Multibly() method only.
del(5, 5);
}
}
}

Tutorial 11:Interfaces

An interface looks like a class, but has no implementation. The only thing it contains are definitions of events, indexers, methods and/or properties.

Defining an Interface: MyInterface.cs

interface IMyInterface
{
void MethodToImplement();
}

Using an Interface: InterfaceImplementer.cs

class InterfaceImplementer : IMyInterface
{
static void Main()
{
InterfaceImplementer iImp = new InterfaceImplementer();
iImp.MethodToImplement();
}

public void MethodToImplement()
{
Console.WriteLine("MethodToImplement() called.");
}
}

Interface Inheritance
using System;

interface IParentInterface
{
void ParentInterfaceMethod();
}

interface IMyInterface : IParentInterface
{
void MethodToImplement();
}

class InterfaceImplementer : IMyInterface
{
static void Main()
{
InterfaceImplementer iImp = new InterfaceImplementer();
iImp.MethodToImplement();
iImp.ParentInterfaceMethod();
}

public void MethodToImplement()
{
Console.WriteLine("MethodToImplement() called.");
}

public void ParentInterfaceMethod()
{
Console.WriteLine("ParentInterfaceMethod() called.");
}
}

Tutorial 10:Indexers

C# introduces a new concept known as Indexers which are used for treating an object as an array. The indexers are usually known as smart arrays in C# community. Defining a C# indexer is much like defining properties. We can say that an indexer is a member that enables an object to be indexed in the same way as an array.

this [argument list]
{
get
{
// Get codes goes here
}
set
{
// Set codes goes here
}
}

Where the modifier can be private, public, protected or internal. The return type can be any valid C# types. The 'this' is a special keyword in C# to indicate the object of the current class. The formal-argument-list specifies the parameters of the indexer. The formal parameter list of an indexer corresponds to that of a method, except that at least one parameter must be specified, and that the ref and out parameter modifiers are not permitted. Remember that indexers in C# must have at least one parameter. Other wise the compiler will generate a compilation error.
The following program shows a C# indexer in action

// C#: INDEXER

using System;
using System.Collections;

class MyClass
{
private string []data = new string[5];
public string this [int index]
{
get
{
return data[index];
}
set
{
data[index] = value;
}
}
}


class MyClient
{
public static void Main()
{
MyClass mc = new MyClass();
mc[0] = "Rajesh";
mc[1] = "A3-126";
mc[2] = "Snehadara";
mc[3] = "Irla";
mc[4] = "Mumbai";
Console.WriteLine("{0},{1},{2},{3},{4}",mc[0],mc[1],mc[2],mc[3],mc[4]);
}
}

The indexers in C# can be overloaded just like member functions. The formal parameter list of an indexer defines the signature of the indexer. Specifically, the signature of an indexer consists of the number and types of its formal parameters. The element type is not part of an indexer's signature, nor is the names of the formal parameters. The signature of an indexer must differ from the signatures of all other indexers declared in the same class. C# do not have the concept of static indexers. If we declare an indexer static, the compiler will show a compilation time error.

Tutorial 9:Properties

Properties allow you to access objects state with field-like syntax.
Accessing Class Fields With Properties.
using System;

public class Customer
{
private int m_id = -1;

public int ID
{
get
{
return m_id;
}
set
{
m_id = value;
}
}

private string m_name = string.Empty;

public string Name
{
get
{
return m_name;
}
set
{
m_name = value;
}
}
}

public class CustomerManagerWithProperties
{
public static void Main()
{
Customer cust = new Customer();

cust.ID = 1;
cust.Name = "Amelio Rosales";

Console.WriteLine(
"ID: {0}, Name: {1}",
cust.ID,
cust.Name);

Console.ReadKey();
}
}
It shows how to create and use a property. The Customer class has the ID and Name property implementations. There are also private fields named m_id and m_name; which ID and Name, respectively, encapsulate. Each property has two accessors, get and set. The accessor returns the value of a field. The set accessor sets the value of a field with the contents of value, which is the value being assigned by calling code. The value shown in the accessor is a C# reserved word.
When setting a property, just assign a value to the property as if it were a field. The CustomerManagerWithProperties class uses the ID and Name properties in the Customer class. The first line of Main instantiates a Customer object named cust. Next the value of the m_id and m_name fields of cust are set by using the ID and Name properties.
To read from a property, use the property as if it were a field. Console.WriteLine prints the value of the m_id and m_name fields of cust. It does this by calling the ID and Name properties of cust.
This was a read/write property, but you can also create read-only properties

Read-Only Properties
using System;

public class Customer
{
private int m_id = -1;
private string m_name = string.Empty;

public Customer(int id, string name)
{
m_id = id;
m_name = name;
}

public int ID
{
get
{
return m_id;
}
}

public string Name
{
get
{
return m_name;
}
}
}

public class ReadOnlyCustomerManager
{
public static void Main()
{
Customer cust = new Customer(1, "Amelio Rosales");

Console.WriteLine(
"ID: {0}, Name: {1}",
cust.ID,
cust.Name);

Console.ReadKey();
}
}

Creating a Write-Only Property
using System;

public class Customer
{
private int m_id = -1;

public int ID
{
set
{
m_id = value;
}
}

private string m_name = string.Empty;

public string Name
{
set
{
m_name = value;
}
}

public void DisplayCustomerData()
{
Console.WriteLine("ID: {0}, Name: {1}", m_id, m_name);
}
}

public class WriteOnlyCustomerManager
{
public static void Main()
{
Customer cust = new Customer();

cust.ID = 1;
cust.Name = "Amelio Rosales";

cust.DisplayCustomerData();

Console.ReadKey();
}
}

Auto-Impemented Properties
using System;

public class Customer
{
public int ID { get; set; }
public string Name { get; set; }
}

public class AutoImplementedCustomerManager
{
static void Main()
{
Customer cust = new Customer();

cust.ID = 1;
cust.Name = "Amelio Rosales";

Console.WriteLine(
"ID: {0}, Name: {1}",
cust.ID,
cust.Name);

Console.ReadKey();
}
}

Tutorial 8:Polymorphism

A virtual method in C# specifies an implementation of a method that can be polymorphicaly overridden derived method. A non-virtual method can’t be polymorphically override in a Derived class.

A virtual method can be declared by using the keyword virtual as follows.

class Base
{
public virtual void Method()
{
}
}

When we declare a virtual method, it must contain a method body. Other wise the compiler will generate an error. Remember that, since virtual methods are used for achieving polymorphism and since polymorphism works only with objects, it not possible to declare a static method as virtual in C#. Similarly the private methods are also not possible to declare virtual, since they can’t override inside a derived class.

In C#, it is not necessary to override a Base class virtual method inside a Derived class.

The following program will work absolutely correct.

// Inheritance : Virtual methods

using System;
class Base
{
public virtual void Method()
{
Console.WriteLine("Base method");
}
}
class Derived : Base
{
}
class MyClient
{
public static void Main()
{
Derived d1 = new Derived();
d1.Method(); // Displays 'Base Method'
}
}

Or even it is possible to override a virtual method non-polymorphically inside a Derived class as shown below.

// Inheritance : Virtual methods

using System;
class Base
{
public virtual void Method()
{
Console.WriteLine("Base method");
}
}
class Derived : Base
{
public virtual void Method()
{
Console.WriteLine("Derived method");
}
}
class MyClient
{
public static void Main()
{
Derived d1 = new Derived();
d1.Method(); // Displays 'Derived Method'
}
}

Even it is possible to omit the keyword virtual from the Derived class method or it is possible to declare the Derived class method as new.

When we want to override a virtual method polymorphically inside a Derived class, we have to use the keyword override along with the method declaration. The example is shown below.

In C#, a Base class reference can hold an object of the Derived class and when it invokes the methods, it will invoke always the Derived class methods, if you already override that method inside the Derived class by using the override keyword. Also the Base class method must declare using the keyword virtual. This is what is known as Polymorphism in C#.

// Inheritance : Virtual methods/Polymorphism

using System;
class Base
{
public virtual void Method()
{
Console.WriteLine("Base method");
}
}
class Derived : Base
{
public override void Method()
{
Console.WriteLine("Derived method");
}
}
class MyClient
{
public static void Main()
{
Base b1 = new Derived();
b1.Method(); // Displays 'Base Method'
}
}

As with a virtual method, we must include a method body with an override method; other wise the compiler will generate an error during compilation.

Remember that in C#, we can use the override keyword with only virtual method, when overriding inside a Derived class. An overridden declaration must be identical in every way to the virtual method, it overrides. They must have the same access level; the same return type, the same name and same method signature.

The overridden methods are implicitly virtual in nature and hence they can override in subsequent Derived classes. As like virtual methods, override methods can’t be declared as static or private.

Tutorial 7:Class Inheritance

Inheritance is one of the primary concepts of object-oriented programming. It allows you to reuse existing code. Through effective employment of reuse, you can save time in your programming.
Inheritance consists of creating a class whose primary definition or behavior is based on another class. In other words, inheritance starts by having a class that can provide behavior that other classes can improve on.

Inheritance: BaseClass.cs
using System;

public class ParentClass
{
public ParentClass()
{
Console.WriteLine("Parent Constructor.");
}

public void print()
{
Console.WriteLine("I'm a Parent Class.");
}
}

public class ChildClass : ParentClass
{
public ChildClass()
{
Console.WriteLine("Child Constructor.");
}

public static void Main()
{
ChildClass child = new ChildClass();

child.print();
}
}
Output:
Parent Constructor.
Child Constructor.
I'm a Parent Class.
It shows two classes. The top class is named ParentClass and the main class is called ChildClass. What we want to do is create a child class, using existing code from ParentClass.
First we must declare our intention to use ParentClass as the base class of ChildClass. This is accomplished through the ChildClass declaration public class ChildClass : ParentClass. The base class is specified by adding a colon, ":", after the derived class identifier and then specifying the base class name.
C# supports single class inheritance only. Therefore, you can specify only one base class to inherit from.
ChildClass has exactly the same capabilities as ParentClass. Because of this, you can also say ChildClass "is" a ParentClass. This is shown in the Main() method of ChildClass when the print() method is called. ChildClass does not have its own print() method, so it uses the ParentClass print() method. You can see the results in the 3rd line of output.
Base classes are automatically instantiated before derived classes. Notice the output,The ParentClass constructor executed before the ChildClass constructor.

Derived Class Communicating with Base Class with base keyword
using System;

public class Parent
{
string parentString;
public Parent()
{
Console.WriteLine("Parent Constructor.");
}
public Parent(string myString)
{
parentString = myString;
Console.WriteLine(parentString);
}
public void print()
{
Console.WriteLine("I'm a Parent Class.");
}
}

public class Child : Parent
{
public Child() : base("From Derived")
{
Console.WriteLine("Child Constructor.");
}
public new void print()
{
base.print();
Console.WriteLine("I'm a Child Class.");
}
public static void Main()
{
Child child = new Child();
child.print();
((Parent)child).print();
}
}
Output:
From Derived
Child Constructor.
I'm a Parent Class.
I'm a Child Class.
I'm a Parent Class.
In summary, you know how to create a derived/base class relationship. You can control instantiation of your base class and call its methods either implicitly or explicitly. You also understand that a derived class is a specialization of its base class.

Tutorial 6:Introduction to Classes

Example C# Classes: Classes.cs
// Namespace Declaration
using System;

// helper class
class OutputClass
{
string myString;

// Constructor
public OutputClass(string inputString)
{
myString = inputString;
}

// Instance Method
public void printString()
{
Console.WriteLine("{0}", myString);
}

// Destructor
~OutputClass()
{
// Some resource cleanup routines
}
}

// Program start class
class ExampleClass
{
// Main begins program execution.
public static void Main()
{
// Instance of OutputClass
OutputClass outCl = new OutputClass("This is printed by the output class.");

// Call Output class' method
outCl.printString();
}
}
The top class, OutputClass, has a constructor, instance method, and a destructor. It also had a field named myString. Notice how the OutputClass constructor is used to initialize data members of the class. In this case, the OutputClass constructor accepts a string argument, inputString. This string is copied to the class field myString.
Constructors are not mandatory, as indicated by the implementation of ExampleClass. In this case, a default constructor is provided. A default constructor is simply a constructor with no arguments.
In C#, there are two types of class members, instance and static. Instance class members belong to a specific occurrence of a class. Every time you declare an object of a certain class, you create a new instance of that class. The ExampleClass Main() method creates an instance of the OutputClass named outCl. You can create multiple instances of OutputClass with different names. Each of these instances are separate and stand alone. For example, if you create two OutputClass instances as follows:
OutputClass oc1 = new OutputClass("OutputClass1");
OutputClass oc2 = new OutputClass("OutputClass2");
You create two separate instances of OutputClass with separate myString fields and separate printString() methods. On the other hand, if a class member is static, you can access it simply by using the syntax .. The instance names are oc1 and oc2.
Suppose OutputClass had the following static method:
public static void staticPrinter()
{
Console.WriteLine("There is only one of me.");
}
Then you could call that function from Main() like this:
OutputClass.staticPrinter();
You must call static class members through their class name and not their instance name. This means that you don't need to instantiate a class to use its static members. There is only ever one copy of a static class member. A good use of static members is when there is a function to be performed and no intermediate state is required, such as math calculations. Matter of fact, the .NET Frameworks Base Class Library includes a Math class that makes extensive use of static members.
Another type of constructor is the static constructor. Use static constructor to initialize static fields in a class. You declare a static constructor by using the keyword static just in front of the constructor name. A static constructor is called before an instance of a class is created, before a static member is called, and before the static constructor of a derived class (covered in a later chapter). They are called only once.
OutputClass also has a destructor. Destructors look just like constructors, except they have a tilde, "~", in front of them. They don't take any parameters and do not return a value. Destructors are places where you could put code to release any resources your class was holding during its lifetime. They are normally called when the C# garbage collector decides to clean your object from memory.
In summary, you can declare instance and static constructors. You know how to initialize class fields. When there is no need to instantiate an object, you can create static class members. You can also declare destructors for cleaning up resources.

Tutorial 5:Namespaces

Namespaces are C# program elements designed to help you organize your programs. They also provide assistance in avoiding name clashes between two sets of code. Implementing Namespaces in your own code is a good habit because it is likely to save you from problems later when you want to reuse some of your code.
// Namespace Declaration
using System;

// The Portal-management Namespace
namespace Portal-management
{
// Program start class
class NamespaceCSS
{
// Main begins program execution.
public static void Main()
{
// Write to console
Console.WriteLine("This is the new Portal-management Namespace.");
}
}
}
It shows how to create a namespace. We declare the new namespace by putting the word namespace in front of Portal-management. Curly braces surround the members inside the Portal-management namespace.

Nested Namespace
// Namespace Declaration
using System;

// The Portal-management Tutorial Namespace
namespace Portal-management
{
namespace tutorial
{
// Program start class
class NamespaceCSS
{
// Main begins program execution.
public static void Main()
{
// Write to console
Console.WriteLine("This is the new Portal-management Tutorial Namespace.");
}
}
}
}

Another Way to create Namespace using "." operator i.e Portal-management.tutorial
// Namespace Declaration
using System;

// The Portal-management Tutorial Namespace
namespace Portal-management.tutorial
{
// Program start class
class NamespaceCSS
{
// Main begins program execution.
public static void Main()
{
// Write to console
Console.WriteLine("This is the new Portal-management Tutorial Namespace.");
}
}
}
It shows another way of writing nested namespaces. It specifies the nested namespace with the dot operator between Portal-management and tutorial.

Calling Namespace Members: NamespaceCall.cs
// Namespace Declaration
using System;

namespace Portal-management
{
// nested namespace
namespace tutorial
{
class myExample1
{
public static void myPrint1()
{
Console.WriteLine("First Example of calling another namespace member.");
}
}
}

// Program start class
class NamespaceCalling
{
// Main begins program execution.
public static void Main()
{
// Write to console
tutorial.myExample1.myPrint1();
tutorial.myExample2.myPrint2();
}
}
}

// same namespace as nested namespace above
namespace Portal-management.tutorial
{
class myExample2
{
public static void myPrint2()
{
Console.WriteLine("Second Example of calling another namespace member.");
}
}
}

Another way to calling namespaces with the help of "using" keyword or with the Alias Directive:

// Namespace Declaration
using System;
using Portal-management.tutorial;

// Program start class
class UsingDirective
{
// Main begins program execution.
public static void Main()
{
// Call namespace member
myExample.myPrint();
}
}

// Portal-management Tutorial Namespace
namespace Portal-management.tutorial
{
class myExample
{
public static void myPrint()
{
Console.WriteLine("Example of using a using directive.");
}
}
}

With the Alias Directive:
// Namespace Declaration
using System;
using csTut = Portal-management.tutorial.myExample; // alias

// Program start class
class AliasDirective
{
// Main begins program execution.
public static void Main()
{
// Call namespace member
csTut.myPrint();
myPrint();
}

// Potentially ambiguous method.
static void myPrint()
{
Console.WriteLine("Not a member of Portal-management.tutorial.myExample.");
}
}

// Portal-management Tutorial Namespace
namespace Portal-management.tutorial
{
class myExample
{
public static void myPrint()
{
Console.WriteLine("This is a member of Portal-management.tutorial.myExample.");
}
}
}

In summary, you know what a namespace is and you can declare your own namespaces. If you don't want to type a fully qualified name, you know how to implement the using directive. When you want to shorten a long namespace declaration, you can use the alias directive. Also, you have been introduced to some of the other namespace members in addition to the class type.

Tutorial 4:Methods

Methods are extremely useful because they allow you to separate your logic into different units. You can pass information to methods, have it perform one or more statements, and retrieve a return value.
Here's a description of the syntax required for creating a method:
attributes modifiers return-type method-name(parameters )
{
statements
}

The return-type can be any C# type. It can be assigned to a variable for use later in the program. The method name is a unique identifier for what you wish to call a method.Parameters allow you to pass information to and from a method.Statements within the curly braces carry out the functionality of the method.
One Simple Method: OneMethod.cs

using System;
class OneMethod
{
public static void Main()
{
string myChoice;

OneMethod om = new OneMethod();

do
{
myChoice = om.getChoice();

// Make a decision based on the user's choice
switch(myChoice)
{
case "A":
case "a":
Console.WriteLine("You wish to add an address.");
break;
case "D":
case "d":
Console.WriteLine("You wish to delete an address.");
break;
case "M":
case "m":
Console.WriteLine("You wish to modify an address.");
break;
case "V":
case "v":
Console.WriteLine("You wish to view the address list.");
break;
case "Q":
case "q":
Console.WriteLine("Bye.");
break;
default:
Console.WriteLine("{0} is not a valid choice", myChoice);
break;
}

// Pause to allow the user to see the results
Console.WriteLine();
Console.Write("press Enter key to continue...");

Console.ReadLine();
Console.WriteLine();

} while (myChoice != "Q" && myChoice != "q"); // Keep going until the user wants to quit
}

string getChoice()
{
string myChoice;
// Print A Menu
Console.WriteLine("My Address Book\n");
Console.WriteLine("A - Add New Address");
Console.WriteLine("D - Delete Address");
Console.WriteLine("M - Modify Address");
Console.WriteLine("V - View Addresses");
Console.WriteLine("Q - Quit\n");
Console.Write("Choice (A,D,M,V,or Q): ");
// Retrieve the user's choice
myChoice = Console.ReadLine();
Console.WriteLine();

return myChoice;
}
}

Instead of printing the menu and accepting input in the Main() method, this functionality has been moved to a new method called getChoice(). The return type is a string. This string is used in the switch statement in Main(). The method name "getChoice" describes what happens when it is invoked. Since the parentheses are empty, no information will be transferred to the getChoice() method.
Within the method block we first declare the variable myChoice. Although this is the same name and type as the myChoice variable in Main(), they are both unique variables. They are local variables and they are visible only in the block they are declared. In other words, the myChoice in getChoice() knows nothing about the existence of the myChoice in Main(), and vice versa.
The getChoice() method prints a menu to the console and gets the user's input. The return statement sends the data from the myChoice variable back to the caller, Main(), of getChoice(). Notice that the type returned by the return statement must be the same as the return-type in the function declaration. In this case it is a string.
In the Main() method we must instantiate a new OneMethod object before we can use getChoice(). This is because of the way getChoice() is declared. Since we did not specify a static modifier, as for Main(), getChoice() becomes an instance method. The difference between instance methods and static methods is that multiple instances of a class can be created (or instantiated) and each instance has its own separate getChoice() method. However, when a method is static, there are no instances of that method, and you can invoke only that one definition of the static method.
So, as stated, getChoice() is not static and therefore, we must instantiate a new object to use it. This is done with the declaration OneMethod om = new OneMethod(). On the left hand side of the declaration is the object reference om which is of type OneMethod. The distinction of om being a reference is important. It is not an object itself, but it is a variable that can refer (or point ) to an object of type OneMethod. On the right hand side of the declaration is an assignment of a new OneMethod object to the reference om. The keyword new is a C# operator that creates a new instance of an object on the heap. What is happening here is that a new OneMethod instance is being created on the heap and then being assigned to the om reference. Now that we have an instance of the OneMethod class referenced by om, we can manipulate that instance through the om reference. Methods, fields, and other class members can be accessed, identified, or manipulated through the "." (dot) operator. Since we want to call getChoice(), we do so by using the dot operator through the om reference: om.getChoice(). The program then executes the statements in the getChoice() block and returns. To capture the value getChoice() returns, we use the "=" (assignment) operator. The returned string is placed into Main()'s local myChoice variable. From there, the rest of the program executes as expected, using concepts from earlier lessons.
Method Parameters: MethodParams.cs

using System;

class Address
{
public string name;
public string address;
}

class MethodParams
{
public static void Main()
{
string myChoice;

MethodParams mp = new MethodParams();

do
{
// show menu and get input from user
myChoice = mp.getChoice();

// Make a decision based on the user's choice
mp.makeDecision(myChoice);

// Pause to allow the user to see the results
Console.Write("press Enter key to continue...");
Console.ReadLine();
Console.WriteLine();
} while (myChoice != "Q" && myChoice != "q"); // Keep going until the user wants to quit
}

// show menu and get user's choice
string getChoice()
{
string myChoice;

// Print A Menu
Console.WriteLine("My Address Book\n");

Console.WriteLine("A - Add New Address");
Console.WriteLine("D - Delete Address");
Console.WriteLine("M - Modify Address");
Console.WriteLine("V - View Addresses");
Console.WriteLine("Q - Quit\n");

Console.WriteLine("Choice (A,D,M,V,or Q): ");

// Retrieve the user's choice
myChoice = Console.ReadLine();

return myChoice;
}

// make decision
void makeDecision(string myChoice)
{
Address addr = new Address();

switch(myChoice)
{
case "A":
case "a":
addr.name = "Joe";
addr.address = "Portal-management";
this.addAddress(ref addr);
break;
case "D":
case "d":
addr.name = "Robert";
this.deleteAddress(addr.name);
break;
case "M":
case "m":
addr.name = "Matt";
this.modifyAddress(out addr);
Console.WriteLine("Name is now {0}.", addr.name);
break;
case "V":
case "v":
this.viewAddresses("Cheryl", "Joe", "Matt", "Robert");
break;
case "Q":
case "q":
Console.WriteLine("Bye.");
break;
default:
Console.WriteLine("{0} is not a valid choice", myChoice);
break;
}
}

// insert an address
void addAddress(ref Address addr)
{
Console.WriteLine("Name: {0}, Address: {1} added.", addr.name, addr.address);
}

// remove an address
void deleteAddress(string name)
{
Console.WriteLine("You wish to delete {0}'s address.", name);
}

// change an address
void modifyAddress(out Address addr)
{
//Console.WriteLine("Name: {0}.", addr.name); // causes error!
addr = new Address();
addr.name = "Joe";
addr.address = "Portal-management";
}

// show addresses
void viewAddresses(params string[] names)
{
foreach (string name in names)
{
Console.WriteLine("Name: {0}", name);
}
}
}

There are 4 kinds of parameters a C# method can handle: out, ref, params, and value. To help illustrate usage of parameters, we created an Address class with two string fields.
In Main() we call getChoice() to get the user's input and put that string in the myChoice variable. Then we use myChoice as an argument to makeDecision(). In the declaration of makeDecision() you'll notice its one parameter is declared as a string with the name myChoice. Again, this is a new myChoice, separate from the caller's argument and local only to this method. Since makeDecision()'s myChoice parameter does not have any other modifiers, it is considered a value parameter. The actual value of the argument is copied on the stack. Variables given by value parameters are local and any changes to that local variable do not affect the value of the variable used in the caller's argument.
The switch statement in makeDecision() calls a method for each case. These method calls are different from the ones we used in Main(). Instead of using the mp reference, they use the this keyword. this is a reference to the current object. We know the current object has been instantiated because makeDecision() is not a static method. Therefore, we can use the this reference to call methods within the same instance.
The addAddress() method takes a ref parameter. This means that a reference to the parameter is copied to the method. This reference still refers to the same object on the heap as the original reference used in the caller's argument. This means any changes to the local reference's object also changes the caller reference's object. The code can't change the reference, but it can make changes to the object being referenced. You can think of this as a way to have an input/output parameter.
As you know, methods have return values, but sometimes you'll want to return more than one value from a method. An out parameter allows you to return additional values from a method.
modifyAddress() has an out parameter. out parameters are only passed back to the calling function. Because of definite assignment rules, you cannot use this variable until it has a valid value assigned. The first line in modifyAddress() is commented on purpose to illustrate this point. Uncomment it and compile to see what happens. Once assigned and the program returns, the value of the out parameter will be copied into the caller's argument variable. You must assign a value to an out parameter before your method returns.
A very useful addition to the C# language is the params parameter, which lets you define a method that can accept a variable number of arguments. The params parameter must be a single dimension or jagged array. When calling viewAddresses(), we pass in four string arguments. The number of arguments is variable and will be converted to a string[] automatically. In viewAddresses() we use a foreach loop to print each of these strings. Instead of the list of string arguments, the input could have also been a string array. The params parameter is considered an input only parameter and any changes affect the local copy only. In summary, you understand the structure of a method. The four types of paramters are value, ref, out, and params. When you wish to use an instance method, you must instantiate its object as opposed to static methods that can be called any time. The this reference refers to its containing object and may be used to refer to its containing object's members, including methods.

Tutorial 3:Control Statements - Selection

The if Statement:
using System;

class IfSelect
{
public static void Main()
{
string myInput;
int myInt;

Console.Write("Please enter a number: ");
myInput = Console.ReadLine();
myInt = Int32.Parse(myInput);

// Single Decision and Action with braces
if (myInt > 0)
{
Console.WriteLine("Your number {0} is greater than zero.", myInt);
}

// Single Decision and Action without brackets
if (myInt < 0)
Console.WriteLine("Your number {0} is less than zero.", myInt);

// Either/Or Decision
if (myInt != 0)
{
Console.WriteLine("Your number {0} is not equal to zero.", myInt);
}
else
{
Console.WriteLine("Your number {0} is equal to zero.", myInt);
}

// Multiple Case Decision
if (myInt < 0 || myInt == 0)
{
Console.WriteLine("Your number {0} is less than or equal to zero.", myInt);
}
else if (myInt > 0 && myInt <= 10)
{
Console.WriteLine("Your number {0} is in the range from 1 to 10.", myInt);
}
else if (myInt > 10 && myInt <= 20)
{
Console.WriteLine("Your number {0} is in the range from 11 to 20.", myInt);
}
else if (myInt > 20 && myInt <= 30)
{
Console.WriteLine("Your number {0} is in the range from 21 to 30.", myInt);
}
else
{
Console.WriteLine("Your number {0} is greater than 30.", myInt);
}
}
}

The switch Statement:
using System;

class SwitchSelect
{
public static void Main()
{
string myInput;
int myInt;

begin:

Console.Write("Please enter a number between 1 and 3: ");
myInput = Console.ReadLine();
myInt = Int32.Parse(myInput);

// switch with integer type
switch (myInt)
{
case 1:
Console.WriteLine("Your number is {0}.", myInt);
break;
case 2:
Console.WriteLine("Your number is {0}.", myInt);
break;
case 3:
Console.WriteLine("Your number is {0}.", myInt);
break;
default:
Console.WriteLine("Your number {0} is not between 1 and 3.", myInt);
break;
}

decide:

Console.Write("Type \"continue\" to go on or \"quit\" to stop: ");
myInput = Console.ReadLine();

// switch with string type
switch (myInput)
{
case "continue":
goto begin;
case "quit":
Console.WriteLine("Bye.");
break;
default:
Console.WriteLine("Your input {0} is incorrect.", myInput);
goto decide;
}
}
}


The while Loop:
using System;

class WhileLoop
{
public static void Main()
{
int myInt = 0;

while (myInt < 10)
{
Console.Write("{0} ", myInt);
myInt++;
}
Console.WriteLine();
}
}

The do Loop:
using System;

class DoLoop
{
public static void Main()
{
string myChoice;

do
{
// Print A Menu
Console.WriteLine("My Address Book\n");

Console.WriteLine("A - Add New Address");
Console.WriteLine("D - Delete Address");
Console.WriteLine("M - Modify Address");
Console.WriteLine("V - View Addresses");
Console.WriteLine("Q - Quit\n");

Console.WriteLine("Choice (A,D,M,V,or Q): ");

// Retrieve the user's choice
myChoice = Console.ReadLine();

// Make a decision based on the user's choice
switch(myChoice)
{
case "A":
case "a":
Console.WriteLine("You wish to add an address.");
break;
case "D":
case "d":
Console.WriteLine("You wish to delete an address.");
break;
case "M":
case "m":
Console.WriteLine("You wish to modify an address.");
break;
case "V":
case "v":
Console.WriteLine("You wish to view the address list.");
break;
case "Q":
case "q":
Console.WriteLine("Bye.");
break;
default:
Console.WriteLine("{0} is not a valid choice", myChoice);
break;
}

// Pause to allow the user to see the results
Console.Write("press Enter key to continue...");
Console.ReadLine();
Console.WriteLine();
} while (myChoice != "Q" && myChoice != "q"); // Keep going until the user wants to quit
}
}

The for Loop:
using System;

class ForLoop
{
public static void Main()
{
for (int i=0; i < 20; i++)
{
if (i == 10)
break;

if (i % 2 == 0)
continue;

Console.Write("{0} ", i);
}
Console.WriteLine();
}
}

The foreach Loop:
A foreach loop is used to iterate through the items in a list. It operates on arrays or collections such as ArrayList, which can be found in the System.Collections namespace. The syntax of a foreach loop is foreach ( in ) { }. The type is the type of item contained in the list. For example, if the type of the list was int[] then the type would be int.
The iteration variable is an identifier that you choose, which could be anything but should be meaningful. For example, if the list contained an array of people's ages, then a meaningful name for item name would be age.
The in keyword is required.
using System;

class ForEachLoop
{
public static void Main()
{
string[] names = {"Cheryl", "Joe", "Matt", "Robert"};

foreach (string person in names)
{
Console.WriteLine("{0} ", person);
}
}
}

Summary:
Loops allow you to execute a block of statements repeatedly. C# offers several statements to construct loops with, including the while, do, for, and foreach loops. while loops execute a block of statements as long as an expression is true, do loops execute a block of statements at least once and then keep going as long as a condition is true, for loops execute a block of statements a specified amount of times, and foreach loops execute a block of statements for each item in a collection. Normally a block of statements will execute from beginning to end. However, the normal flow of a loop can be changed with the break and continue statements.

Tutorial 2:Operators, Types, and Variables

Variables and Types:
"Variables" are simply storage locations for data. You can place data into them and retrieve their contents as part of a C# expression. The interpretation of the data in a variable is controlled through "Types".
Integral Types
In C#, an integral is a category of types. For anyone confused because the word Integral sounds like a mathematical term, from the perspective of C# programming, these are actually defined as Integral types in the C# programming language specification. They are whole numbers, either signed or unsigned, and the char type. The char type is a Unicode character, as defined by the Unicode Standard.
The Size and Range of C# Integral Types-

Type Size (in bits) Range
sbyte 8 -128 to 127
byte 8 0 to 255
short 16 -32768 to 32767
ushort 16 0 to 65535
int 32 -2147483648 to 2147483647
uint 32 0 to 4294967295
long 64 -9223372036854775808 to 9223372036854775807
ulong 64 0 to 18446744073709551615
char 16 0 to 65535

Integral types are well suited for those operations involving whole number calculations. The char type is the exception, representing a single Unicode character. As you can see from the table above, you have a wide range of options to choose from, depending on your requirements.

Floating Point and Decimal Types:
A C# floating point type is either a float or double. They are used any time you need to represent a real number, as defined by IEEE 754. For more information on IEEE 754, visit the IEEE Web Site. Decimal types should be used when representing financial or money values. table 2-2 shows the floating point and decimal types, their size, precision, and range.
The Floating Point and Decimal Types with Size, precision, and Range
Type Size (in bits) precision Range
float 32 7 digits 1.5 x 10-45 to 3.4 x 1038
double 64 15-16 digits 5.0 x 10-324 to 1.7 x 10308
decimal 128 28-29 decimal places 1.0 x 10-28 to 7.9 x 1028

Floating point types are used when you need to perform operations requiring fractional representations. However, for financial calculations, the decimal type is the best choice because you can avoid rounding errors.


The Boolean Type :
Boolean types are declared using the keyword, bool. They have two values: true or false. In other languages, such as C and C++, boolean conditions can be satisfied where 0 means false and anything else means true. However, in C# the only values that satisfy a boolean condition is true and false, which are official keywords. Listing 2-1 shows one of many ways that boolean types can be used in a program.
using System;

class Booleans
{
public static void Main()
{
bool content = true;
bool noContent = false;

Console.WriteLine("It is {0} that Portal-management provides C# programming language content.", content);
Console.WriteLine("The statement above is not {0}.", noContent);
}
}
, the boolean values are written to the console as a part of a sentence. The only legal values for the bool type are either true or false, as shown by the assignment of true to content and false to noContent. When run, this program produces the following output:
It is True that Portal-management provides C# programming language content.
The statement above is not False.

The string Type:
A string is a sequence of text characters. You typically create a string with a string literal, enclosed in quotes: "This is an example of a string." You've seen strings being used in Lesson 1, where we used the Console.WriteLine method to send output to the console.
Some characters aren't printable, but you still need to use them in strings. Therefore, C# has a special syntax where characters can be escaped to represent non-printable characters. For example, it is common to use newlines in text, which is represented by the '\n' char. The backslash, '\', represents the escape. When preceded by the escape character, the 'n' is no longer interpreted as an alphabetical character, but now represents a newline.
You may be now wondering how you could represent a backslash character in your code. We have to escape that too by typing two backslashes, as in '\\'.
Escape Sequence Meaning
\' Single Quote
\" Double Quote
\\ Backslash
\0 Null, not the same as the C# null value
\a Bell
\b Backspace
\f form Feed
\n Newline
\r Carriage Return
\t Horizontal Tab
\v Vertical Tab

Another useful feature of C# strings is the verbatim literal, which is a string with a @ symbol prefix, as in @"Some string". Verbatim literals make escape sequences translate as normal characters to enhance readability. To appreciate the value of verbatim literals, consider a path statement such as "c:\\topdir\\subdir\\subdir\\myapp.exe". As you can see, the backslashes are escaped, causing the string to be less readable. You can improve the string with a verbatim literal, like this: @"c:\topdir\subdir\subdir\myapp.exe".
That is fine, but now you have the problem where quoting text is not as easy. In that case, you would specify double double quotes. For example, the string "copy \"c:\\source file name with spaces.txt\" c:\\newfilename.txt" would be written as the verbatim literal @"copy ""c:\source file name with spaces.txt"" c:\newfilename.txt".

C# Operators
Results are computed by building expressions. These expressions are built by combining variables and operators together into statements. The following table describes the allowable operators, their precedence, and associativity.

Operators with their precedence and Associativity


Left associativity means that operations are evaluated from left to right. Right associativity mean all operations occur from right to left, such as assignment operators where everything to the right is evaluated before the result is placed into the variable on the left.
Most operators are either unary or binary. Unary operators form expressions on a single variable, but binary operators form expressions with two variables.

Unary Operators: Unary.cs

using System;
class Unary
{
public static void Main()
{
int unary = 0;
int preIncrement;
int preDecrement;
int postIncrement;
int postDecrement;
int positive;
int negative;
sbyte bitNot;
bool logNot;

preIncrement = ++unary;
Console.WriteLine("pre-Increment: {0}", preIncrement);

preDecrement = --unary;
Console.WriteLine("pre-Decrement: {0}", preDecrement);

postDecrement = unary--;
Console.WriteLine("Post-Decrement: {0}", postDecrement);

postIncrement = unary++;
Console.WriteLine("Post-Increment: {0}", postIncrement);

Console.WriteLine("Final Value of Unary: {0}", unary);

positive = -postIncrement;
Console.WriteLine("Positive: {0}", positive);

negative = +postIncrement;
Console.WriteLine("Negative: {0}", negative);

bitNot = 0;
bitNot = (sbyte)(~bitNot);
Console.WriteLine("Bitwise Not: {0}", bitNot);

logNot = false;
logNot = !logNot;
Console.WriteLine("Logical Not: {0}", logNot);
}
}
Here's the output :
pre-Increment: 1
pre-Decrement 0
Post-Decrement: 0
Post-Increment: -1
Final Value of Unary: 0
Positive: 1
Negative: -1
Bitwise Not: -1
Logical Not: true

When evaluating expressions, post-increment (x++) and post-decrement (x--) operators return their current value and then apply the operators. However, when using pre-increment (++x) and pre-decrement (--x) operators, the operator is applied to the variable prior to returning the final value.
the unary variable is initialized to zero. When the pre-increment (++x) operator is used, unary is incremented to 1 and the value 1 is assigned to the preIncrement variable. The pre-decrement (--x) operator turns unary back to a 0 and then assigns the value to the preDecrement variable.
When the post-decrement (x--) operator is used, the value of unary, 0, is placed into the postDecrement variable and then unary is decremented to -1. Next the post-increment (x++) operator moves the current value of unary, -1, to the postIncrement variable and then increments unary to 0.
The variable bitNot is initialized to 0 and the bitwise not (~) operator is applied. The bitwise not (~) operator flips the bits in the variable. In this case, the binary representation of 0, "00000000", was transformed into -1, "11111111".
While the (~) operator works by flipping bits, the logical negation operator (!) is a logical operator that works on bool values, changing true to false or false to true. In the case of the logNot variable in Listing 2-2, the value is initialized to false, and the next line applies the logical negation operator, (!), which returns true and reassigns the new value, true, to logNot. Essentially, it is toggling the value of the bool variable, logNot.
The setting of positive is a little tricky. At the time that it is set, the postIncrement variable is equal to -1. Applying the minus (-) operator to a negative number results in a positive number, meaning that postitive will equal 1, instead of -1. The minus operator (-), which is not the same as the pre-decrement operator (--), doesn't change the value of postInc - it just applies a sign negation. The plus operator (+) doesn't affect the value of a number, assigning negative with the same value as postIncrement, -1.
Notice the expression (sbyte)(~bitNot). Any operation performed on types sbyte, byte, short, or ushort return int values. To assign the result into the bitNot variable we had to use a cast, (Type), operator, where Type is the type you wish to convert to (in this case - sbyte). The cast operator is shown as the Unary operator, (T)x, in table 2-4. Cast operators must be performed explicity when you go from a larger type to a smaller type because of the potential for lost data. Generally speaking, assigning a smaller type to a larger type is no problem, since the larger type has room to hold the entire value. Also be aware of the dangers of casting between signed and unsigned types. You want to be sure to preserve the integrity of your data. Many basic programming texts contain good descriptions of bit representations of variables and the dangers of explicit casting.

Binary Operators: Binary.cs
using System;

class Binary
{
public static void Main()
{
int x, y, result;
float floatresult;

x = 7;
y = 5;

result = x+y;
Console.WriteLine("x+y: {0}", result);

result = x-y;
Console.WriteLine("x-y: {0}", result);

result = x*y;
Console.WriteLine("x*y: {0}", result);

result = x/y;
Console.WriteLine("x/y: {0}", result);

floatresult = (float)x/(float)y;
Console.WriteLine("x/y: {0}", floatresult);

result = x%y;
Console.WriteLine("x%y: {0}", result);

result += x;
Console.WriteLine("result+=x: {0}", result);
}
}
And here's the output:
x+y: 12
x-y: 2
x*y: 35
x/y: 1
x/y: 1.4
x%y: 2
result+=x: 9
It shows several examples of binary operators. As you might expect, the results of addition (+), subtraction (-), multiplication (*), and division (/) produce the expected mathematical results.
The floatresult variable is a floating point type. We explicitly cast the integer variables x and y to calculate a floating point value.
There is also an example of the remainder(%) operator. It performs a division operation on two values and returns the remainder.
The last statement shows another form of the assignment with operation (+=) operator. Any time you use the assignment with operation operator, it is the same as applying the binary operator to both the left hand and right hand sides of the operator and putting the results into the left hand side. The example could have been written as result = result + x; and returned the same value.

The Array Type
Another data type is the Array, which can be thought of as a container that has a list of storage locations for a specified type. When declaring an Array, specify the type, name, dimensions, and size.
Array Operations: Array.cs
using System;

class Array
{
public static void Main()
{
int[] myInts = { 5, 10, 15 };
bool[][] myBools = new bool[2][];
myBools[0] = new bool[2];
myBools[1] = new bool[1];
double[,] myDoubles = new double[2, 2];
string[] myStrings = new string[3];

Console.WriteLine("myInts[0]: {0}, myInts[1]: {1}, myInts[2]: {2}", myInts[0], myInts[1], myInts[2]);

myBools[0][0] = true;
myBools[0][1] = false;
myBools[1][0] = true;
Console.WriteLine("myBools[0][0]: {0}, myBools[1][0]: {1}", myBools[0][0], myBools[1][0]);

myDoubles[0, 0] = 3.147;
myDoubles[0, 1] = 7.157;
myDoubles[1, 1] = 2.117;
myDoubles[1, 0] = 56.00138917;
Console.WriteLine("myDoubles[0, 0]: {0}, myDoubles[1, 0]: {1}", myDoubles[0, 0], myDoubles[1, 0]);

myStrings[0] = "Joe";
myStrings[1] = "Matt";
myStrings[2] = "Robert";
Console.WriteLine("myStrings[0]: {0}, myStrings[1]: {1}, myStrings[2]: {2}", myStrings[0], myStrings[1], myStrings[2]);

}
}
And here's the output:
myInts[0]: 5, myInts[1]: 10, myInts[2]: 15
myBools[0][0]: true, myBools[1][0]: true
myDoubles[0, 0]: 3.147, myDoubles[1, 0]: 56.00138917
myStrings[0]: Joe, myStrings[1]: Matt, myStrings[2]: Robert

4 shows different implementations of Arrays. The first example is the myInts Array, which is a single-dimension array. It is initialized at declaration time with explicit values.
Next is a jagged array, myBools. It is essentially an array of arrays. We needed to use the new operator to instantiate the size of the primary array and then use the new operator again for each sub-array.
The third example is a two dimensional array, myDoubles. Arrays can be multi-dimensional, with each dimension separated by a comma. It must also be instantiated with the new operator.
One of the differences between jagged arrays, myBools[][], and multi-dimension arrays, myDoubles[,], is that a multi-dimension array will allocate memory for every element of each dimension, whereas a jagged array will only allocate memory for the size of each array in each dimension that you define. Most of the time, you'll be using multi-dimension arrays, if you need multiple dimensions, and will only use jagged arrays in very special circumstances when you are able to save significant memory by explicitly specifying the sizes of the arrays in each dimension.
Finally, we have the single-dimensional array of string types, myStrings.
In each case, you can see that array elements are accessed by identifying the integer index for the item you wish to refer to. Arrays sizes can be any int type value. Their indexes begin at 0.
A variable is an identifier with a type that holds a value of that type. Simple types include the integrals, floating points, decimal, and bool. C# has several mathematical and logical operators that participate in forming expressions. C# also offers the single dimension, multi-dimension and jagged array types.

Tutorial 1:Getting Started with C#

C# (pronounced "C-sharp") is an object-oriented programming language from Microsoft that aims to combine the computing power of C++ with the programming ease of Visual Basic. C# is based on C++ and contains features similar to those of Java.
C# is case-sensitive.There are basic elements that all C# executable programs have and that's what we'll concentrate on for this first lesson, starting off with a simple C# program.

A Simple Welcome Program: "Welcome.cs" written in a simple notepad

// Namespace Declaration
using System;

// Program start class
class WelcomeCSS
{
// Main begins program execution.
static void Main()
{
// Write to console
Console.WriteLine("Welcome to the Portal-management Tutorial!");
}
}

The program has 4 primary elements, a namespace declaration, a class, a Main method, and a program statement. It can be compiled with the following command line:
csc.exe Welcome.cs

You can find the csc.exe in the following path

C:\Program Files\Microsoft Visual Studio 8\VC
For more help about command line options, type "csc -help" on the command line.

Note for VS.NET Users: The screen will run and close quickly when launching this program from Visual Studio .NET Console Application. To prevent this, add the following code as the last line in the Main method:
// keep screen from going away
// when run from VS.NET
Console.ReadLine();

The first thing you should be aware of is that C# is case-sensitive. The word "Main" is not the same as its lower case spelling, "main". They are different identifiers. If you are coming from a language that is not case sensitive, this will trip you up several times until you become accustomed to it.
The namespace declaration, using System;, indicates that you are referencing the System namespace. Namespaces contain groups of code that can be called upon by C# programs. With the using System; declaration, you are telling your program that it can reference the code in the System namespace without pre-pending the word System to every reference.
The class declaration, class WelcomeCSS, contains the data and method definitions that your program uses to execute.
The one method within the WelcomeCSS class tells what this class will do when executed. The method name, Main, is reserved for the starting point of a program. Main is often called the "entry point" and if you ever receive a compiler error message saying that it can't find the entry point, it means that you tried to compile an executable program without a Main method.
A static modifier precedes the word Main, meaning that this method works in this specific class only, rather than an instance of the class. This is necessary, because when a program begins, no object instances exist.
Every method must have a return type. In this case it is void, which means that Main does not return a value. Every method also has a parameter list following its name with zero or more parameters between parenthesis. For simplicity, we did not add parameters to Main.
The Main method specifies its behavior with the Console.WriteLine(...) statement. Console is a class in the System namespace. WriteLine(...) is a method in the Console class. We use the ".", dot, operator to separate subordinate program elements. Note that we could also write this statement as System.Console.WriteLine(...). This follows the pattern "namespace.class.method" as a fully qualified statement. Had we left out the using System declaration at the top of the program, it would have been mandatory for us to use the fully qualified form System.Console.WriteLine(...). This statement is what causes the string, "Welcome to the Portal-management Tutorial!" to print on the console screen.
Observe that comments are marked with "//". These are single line comments, meaning that they are valid until the end-of-line. If you wish to span multiple lines with a comment, begin with "/*" and end with "*/". Everything in between is part of the comment. Comments are ignored when your program compiles. They are there to document what your program does in plain English (or the native language you speak with every day).
All statements end with a ";", semi-colon. Classes and methods begin with "{", left curly brace, and end with a "}", right curly brace. Any statements within and including "{" and "}" define a block. Blocks define scope (or lifetime and visibility) of program elements.

Accepting Command-Line Input:
In the previous example, you simply ran the program and it produced output. However, many programs are written to accept command-line input. This makes it easier to write automated scripts that can invoke your program and pass information to it.
Following code show you how to handle command-line input
// Namespace Declaration
using System;

// Program start class
class NamedWelcome
{
// Main begins program execution.
static void Main(string[] args)
{
// Write to console
Console.WriteLine("Hello, {0}!", args[0]);
Console.WriteLine("Welcome to the Portal-management Tutorial!");
}
}
If you are running Visual Studio, right-click on the project in Solution Explorer, select Properties, click the Debug tab, locate Start Options, and type YourName into Command line arguments. If you forget to to enter YourName on the command-line or enter it into the project properties, as I just explained, you will receive an exception that says "Index was outside the bounds of the array."
you'll notice an entry in the Main method's parameter list. The parameter name is args, which you'll use to refer to the parameter later in your program. The string[] expression defines the type of parameter that args is. The string type holds characters. These characters could form a single word, or multiple words. The "[]", square brackets denote an Array, which is like a list. Therefore, the type of the args parameter, is a list of words from the command-line. Anytime you add string[] args to the parameter list of the Main method, the C# compiler emits code that parses command-line arguments and loads the command-line arguments into args. By reading args, you have access to all arguments, minus the application name, that were typed on the command-line.
You'll also notice an additional Console.WriteLine(...) statement within the Main method. The argument list within this statement is different than before. It has a formatted string with a "{0}" parameter embedded in it. The first parameter in a formatted string begins at number 0, the second is 1, and so on. The "{0}" parameter means that the next argument following the end quote will determine what goes in that position. Hold that thought, and now we'll look at the next argument following the end quote.
The args[0] argument refers to the first string in the args array. The first element of an Array is number 0, the second is number 1, and so on. For example, if I typed NamedWelcome Manab on the command-line, the value of args[0] would be "Manab". This is a little tricky because you know that you typed NamedWelcome.exe on the command-line, but C# doesn't include the executable application name in the args list - only the first parameter after the executable application.
Returning to the embedded "{0}" parameter in the formatted string: Since args[0] is the first argument, after the formatted string, of the Console.WriteLine() statement, its value will be placed into the first embedded parameter of the formatted string. When this command is executed, the value of args[0], which is "Manab" will replace "{0}" in the formatted string. Upon execution of the command-line with "NamedWelcome Manab", the output will be as follows:
Hello, Manab!
Welcome to the Portal-management Tutorial!

Besides command-line input, another way to provide input to a program is via the Console. Typically, it works like this: You prompt the user for some input, they type something in and press the Enter key, and you read their input and take some action. Following code shows how to obtain interactive input from the user.
// Namespace Declaration
using System;

// Program start class
class InteractiveWelcome
{
// Main begins program execution.
public static void Main()
{
// Write to console/get input
Console.Write("What is your name?: ");
Console.Write("Hello, {0}! ", Console.ReadLine());
Console.WriteLine("Welcome to the Portal-management Tutorial!");
}
}
The Main method doesn't have any parameters -- mostly because it isn't necessary this time. Notice also that I prefixed the Main method declaration with the public keyword. The public keyword means that any class outside of this one can access that class member. For Main, it doesn't matter because your code would never call Main, but as you go through this tutorial, you'll see how you can create classes with members that must be public so they can be used. The default access is private, which means that only members inside of the same class can access it. Keywords such as public and private are referred to as access modifiers.
There are three statements inside of Main and the first two are different from the third. They are Console.Write(...) instead of Console.WriteLine(...). The difference is that the Console.Write(...) statement writes to the console and stops on the same line, but the Console.WriteLine(...) goes to the next line after writing to the console.
The first statement simply writes "What is your name?: " to the console.
The second statement doesn't write anything until its arguments are properly evaluated. The first argument after the formatted string is Console.ReadLine(). This causes the program to wait for user input at the console. After the user types input, their name in this case, they must press the Enter key. The return value from this method replaces the "{0}" parameter of the formatted string and is written to the console. This line could have also been written like this:
string name = Console.ReadLine();
Console.Write("Hello, {0}! ", name);
The last statement writes to the console as described earlier. Upon execution of the command-line with "InteractiveWelcome", the output will be as follows:
>What is your Name? [Enter Key]
>Hello, ! Welcome to the Portal-management Tutorial!

Now you know the basic structure of a C# program. using statements let you reference a namespace and allow code to have shorter and more readable notation. The Main method is the entry point to start a C# program. You can capture command-line input when an application is run by reading items from a string[] (string array) parameter to your Main method. Interactive I/O can be performed with the ReadLine, Write and WriteLine methods of the Console class.