Chapter 3: VB and C# Programming Basics

You may also come across instances in which you need to exit a loop prematurely. In these cases, you would use either Exit, if your code is in VB, or the equivalent (break) statement in C#, to terminate the loop:

Visual Basic

Dim i As Integer

For i = 0 To 10

If (i = 5) Then

Response.Write("Oh no! Not the number 5!!")

Exit For

End If

Next

C#

int i;

for (i = 0; i <= 10; i++)

{

if (i == 5)

{

Response.Write("Oh no! Not the number 5!!"); break;

}

}

In this case, as soon as our For loop hits the condition i = 5, it displays a warning message using the Response.Write method (which will be familiar to those with past ASP experience), and exits the loop so that no further passes through the loop will be made.

Although we’ve only scratched the surface, VB and C# provide a great deal of power and flexibility to web developers, and time spent learning the basics now will more than pay off in the future.

Object Oriented Programming Concepts

VB and C# are modern programming languages that give you the tools to write structured, extensible, and maintainable code. The code can be separated into modules, each of which defines classes that can be imported and used in other modules. Both languages are relatively simple to get started with, yet they offer sophisticated features for writing complex, large-scale enterprise applications.

One of the reasons why these languages are so powerful is that they facilitate object oriented programming (OOP). In this section, we’ll explain the funda-

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Objects and Classes

mentals of OOP and learn how adopting good OOP style now can help you to develop better, more versatile web applications down the road. This section will provide a basic OOP foundation angled towards the web developer. In particular, we’ll cover the following concepts:

objects

properties

methods

classes

scope

events

inheritance

In the pages that follow, we’ll discuss these concepts briefly, and from Chapter 4 onwards, you’ll see some practical examples of OOP in action.

Objects and Classes

So what does the term “object oriented programming” mean? Basically, as the name suggests, it’s an approach to development that puts objects at the center of the programming model. The object is probably the most important concept in the world of OOP; an object is a self-contained entity that has state and behavior, just like a real-world object.

In programming, an object's state is described by its fields and properties, while its behavior is defined by its methods and events. An important part of OOP’s strength comes from the natural way it allows programmers to conceive and design their applications.

We often use objects in our programs to describe real-world objects—we can have objects that represent a car, a customer, a document, or a person. Each object has its own state and behavior.

It’s very important to have a clear understanding of the difference between a class and an object. A class acts like a blueprint for the object, while an object represents an instance of the class. I just said that you could have objects of type

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Chapter 3: VB and C# Programming Basics

Car, for example. If you did, Car would be the class, or the type, and we could create as many Car objects as we wanted, calling them myCar, johnsCar, davesCar, and so on.

The class defines the behavior of all objects of that type. So all objects of type Car will have the same behavior—for example, the ability to change gear. However, each individual Car object may be in a different gear at any particular time; thus, each object has its own particular state.

Let’s take another example: think of Integer (or int) as a class, and age and height as objects of type Integer. The class defines the behavior of the ob- jects—they’re numeric, and we can perform mathematical operations on them—and the instances of objects (age and height) have their behavior defined by the class to which they belong, but they also hold state (so age could be 20).

Take a look at the following code:

Visual Basic

Dim age As Integer

Dim name As String

Dim myCar as Car

Dim myOtherCar as Car

C#

int age; string name; Car myCar;

Car myOtherCar;

As you can see, the syntax for declaring an object is the same as that for declaring a simple integer or string variable. In C#, we first mention the type of the object, then we name that particular instance. In VB, we use the Dim keyword.

Object oriented programming sounds like an advanced topic, but getting started with it is actually very easy, because OOP offers us a natural way to conceive and design programs. Instead of writing long functions of code to perform specific tasks, OOP allows us to group pieces of related functionality into classes that we can reuse over and over, or even extend to incorporate new features. In OOP, one thinks of programming problems in terms of objects, properties, and methods. And, as we’ve seen, the best way to get a handle on these terms is to consider a real-world object and imagine how it might be represented in an OOP program. For the examples that follow, we’ll use as our example my dog, an Australian Shepherd named Rayne.

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Objects and Classes

Rayne is your average great big, friendly, loving, playful mutt. You might describe him in terms of his physical properties: he’s gray, white, brown, and black, stands roughly one-and-a-half feet high, and is about three feet long. You might also describe some methods to make him do things: he sits when he hears the command “Sit,” lies down when he hears the command “Lie down,” and comes when his name is called.

So, if we were to represent Rayne in an OOP program, we’d probably start by creating a class called Dog. A class describes how certain types of objects look from a programming point of view. When we define a class, we must define the following two items:

Properties Properties hold specific information relevant to that class of object. You can think of properties as characteristics of the objects that they represent. Our Dog class might have properties such as Color,

Height, and Length.

Methods Methods are actions that objects of the class can be told to perform. Methods are subroutines (if they don’t return a value) or functions (if they do) that are specific to a given class. So the Dog class could have methods such as Sit, and LieDown.

Once we’ve defined a class, we can write code that creates objects of that class, using the class a little like a template. This means that objects of a particular class expose (or make available) the methods and properties defined by that class. So, we might create an instance of our Dog class called rayne, set its properties accordingly, and use the methods defined by the class to interact with Rayne, as shown in Figure 3.6.

Figure 3.6. An instance of Dog

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