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GVC Ths. Nguyn Minh o

BM CNPM - Khoa CNTT -HSPKT TP.HCM

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C# is a simple, modern, general-purpose,oriented programming language developMicrosoft within its .NET initiative led by AHejlsberg.

This tutorial will teach you basic C# prograand will also take you through various advconcepts related to C# programming languag

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STRINGS

In C#, you can use strings as array of characters, however, mopractice is to use thestring keyword to declare a string variablekeyword is an alias for the System.String class.

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You can create string object using one of thefollowing methods:By assigning a string literal to a Stringvariable

By using a String class constructor

By using the string concatenation operator (+)

By retrieving a property or calling a method threturns a string

By calling a formatting method to convert a valobject to its string representation


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The String class has the following two properties:


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STRUCTURES

In C#, a structure is a value type data type. It helps you to mavariable hold related data of various data types. Thestruct keywfor creating a structure.

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Structures are used to represent a record. Suppose ywant to keep track of your books in a library. You miwant to track the following attributes about each bo

Title

Author

Subject Book ID


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To define a structure, you must use the struct staThe struct statement defines a new data type, withan one member for your program.

For example, here is the way you would declare thstructure:


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You have already used a simple structure namedStructures in C# are quite different from that in traC or C++. The C# structures have the following featStructures can have methods, fields, indexers, pro

operator methods, and events.

Structures can have defined constructors, bdestructors. However, you cannot define aconstructor for a structure. The default constrautomatically defined and can't be changed.

Unlike classes, structures cannot inherit other stror classes.


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You have already used a simple structure namedStructures in C# are quite different from that in traC or C++. The C# structures have the following feat

Structures cannot be used as a base for other stror classes.

A structure can implement one or more interfacesStructure members cannot be specified as avirtual, or protected.


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You have already used a simple structure namedStructures in C# are quite different from that in traC or C++. The C# structures have the following feat

When you create a struct object using theNew oit gets created and the appropriate constructor is

Unlike classes, structs can be instantiated withouthe New operator.

If the New operator is not used, the fields willunassigned and the object cannot be used untilfields are initialized.

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o - Khoa CNTT -

HSPKT TP.HCM

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Classes and Structures have the followingdifferences:

classes are reference types and structs aretypes

structures do not support inheritancestructures cannot have default constructor


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ENUMS

An enumeration is a set of named integer constants. An enumerdeclared using the enum keyword.

C# enumerations are value data type. In other words, enumerationown values and cannot inherit or cannot pass inheritance.

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ENUM

The general syntax for declaring an enumeration is:

Where, The enum_name specifies the enumeration type name.

The enumeration list is a comma-separated list of identifier

Each of the symbols in the enumeration list stands for anvalue, one greater than the symbol that precedes it. Bythe value of the first enumeration symbol is 0.


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ENUM

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CLASSES

When you define a class, you define a blueprint for a data type. This dodefine any data, but it does define what the class name means, that is, whathe class will consist of and what operations can be performed on such an oare instances of a class. The methods and variables that constitute a clamembers of the class.

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A class definition startswith the keyword classfollowed by the classname; and the class body,enclosed by a pair of curly

braces.

Following is the generalform of a class definition:


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Please note that,Access specifiers specify the access rules for the memwell as the class itself, if not mentioned then the defauspecifier for a class type is internal. Default accessmembers isprivate.

Data type specifies the type of variable, and retu

specifies the data type of the data, the method returns To access the class members, you will use the dot (.) o

The dot operator links the name of an object with thea member.


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A member function of a class is a function thatdefinition or its prototype within the class definitany other variable. It operates on any object of the

which it is a member, and has access to all the mema class for that object.

Member variables are attributes of an object (fromperspective) and they are kept private to impencapsulation. These variables can only be accessethe public member functions.


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A classconstructor is a special member funca class that is executed whenever we creaobjects of that class.

A constructor will have exact same name

class and it does not have any return type


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A default constructor does not haveparameter but if you need a constructor caparameters.

Such constructors are called paramet

constructors. This technique helps you toinitial value to an object at the time of its crea


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Adestructor is a special member function ofthat is executed whenever an object of its clasout of scope. Adestructor will have exact samas the class prefixed with a tilde (~) and it canreturn a value nor can it take any parameters.

Destructor can be very useful for releasing resbefore coming out of the program like closinreleasing memories etc. Destructors canninherited or overloaded.


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We can define class members as staticthestatic keyword. When we declare a member of astatic, it means no matter how many objects of the ccreated, there is only one copy of the static member.

The keyword static implies that only one instancemember exists for a class. Static variables are u

defining constants because their values can be retriinvoking the class without creating an instance ofvariables can be initialized outside the member funclass definition. You can also initialize static variablethe class definition.


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INHERITANCE

One of the most important concepts in object-oriented programminheritance. Inheritance allows us to define a class in terms of anwhich makes it easier to create and maintain an application. This aan opportunity to reuse the code functionality and fast implementati

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When creating a class, instead of writing comnew data members and member functionprogrammer can designate that the new classinherit the members of an existing class. This eclass is called the base class, and the new creferred to as thederived class.

The idea of inheritance implements thA relationship. For example, mammal IS AdogIS-A mammal hence dogIS-A animal as wso on.


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A class can be derived from more than one cinterface, which means that it can inherit dafunctionsfrommultiple base classor interface.

The syntax used in C# for creating derived classfollows:


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The derived class inherits the base class mvariables and member methods. Therefosuper class object should be created befosubclass is created.

You can give instructions for supinitialization in the member initialization list.


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C# does not support multiple inherHowever, you can use interfaces to impmultiple inheritance.


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POLYMORPHISM

The word polymorphism means having many forms. In obje

programming paradigm,polymorphism is often expressed as 'on

multiple functions'.

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The word polymorphism means havingforms. In object-oriented programming parpolymorphism is often expressed as 'one intmultiple functions'.

Polymorphism can be static or dynamic. In

polymorphism the response to a functdetermined at the compile time. In dypolymorphism , it is decided at run-time.


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The mechanism of linking a function with anduring compile time is called early bindinalso called static binding.

C# provides two techniques to implementpolymorphism.These are:

Function overloading

Operator overloading

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You can have multiple definitions for thefunction name in the same scope.

The definition of the function must differ fromother by the types and/or the number of arguin the argument list.

You cannot overload function declarationdiffer only by return type.

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C# allows you to create abstract classes thused to provide partial class implementationinterface. Implementation is completed wderived class inherits from it.

Abstract classes contain abstract methods,

are implemented by the derived class. The dclasses have more specialized functionality.

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Please note the following rules about abclasses:

You cannot create an instance of an abstract cla

You cannot declare an abstract method outsabstract class

When a class is declared sealed, it caninherited, abstract classes cannot be declared

ABSTRACT C

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ABSTRACT C

ABSTRACT C

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ABSTRACT C

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When you have a function defined in a clayou want to be implemented in an inhclass(es), you usevirtual functions.

The virtual functions could be implemdifferently in different inherited class and the

these functions will be decided at runtime.

Dynamic polymorphism is implemby abstract classes andvirtual functions.

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