C#.NET Tutorial - Day - 2 - The Basics - First Simple Example "Hello, World!" & Explanation.

If you have ever learned a programming language, you know that they all start with the "Hello, world!" example, and who are we to break such a fine tradition? Start Visual C# Express (introduced in the last Post), and select File -> New project… From the project dialog, select the Console application. This is the most basic application type on a Windows system, but don't worry, we won't stay here for long. Once you click Ok, Visual C# Express creates a new project for you, including a file called Program.cs. This is where all the fun is, and it should look something like this: 

Actually, all these lines doesn't really accomplish anything, or at least it may seem so. Try running the application by pushing F5 on your keyboard. This will make Visual C# Express compile and execute your code, but as you will see, it doesn't do much. You will likely just see a black window launch and close again. That is because our application doesn't do anything yet. In the next chapter we will go through these lines to see what they are all about, but for now, we really would like to see some results, so let's pretend that we know all about C# and add a couple of lines to get some output. Within the last set of { }, add these lines: 

The code of  your first application should now look like this:

Once again, hit F5 to run it, and you will see the black window actually staying, and even displaying our greeting to the world. Okay, so we added two lines of code, but what to they do? One of the nice things about C# and the .NET framework is the fact that a lot of the code makes sense even to the untrained eye, which this example shows. 

The first line uses the Console class to output a line of text, and the second one reads a line of text from the console. Read? Why? Actually this is a bit of a trick, since without it, the application would just end and close the window with the output before anyone could see it. 

The ReadLine command tells the application to wait for input from the user, and as you will notice, the console window now allows you to enter text. Press Enter to close it. Congratulations, you have just created your first C# application! Read on in the next chapter for even more information about what's actually going on.

EXPLANATION 

Above, we tried writing a piece of text to the console, in our first C# application. To see some actual progress, we didn't go into much detail about the lines of code we used, so this chapter is an explanation of the Hello world example code. As you can probably see from the code, some of the lines look similar, so we will bring them back in groups for an individual explanation. Let's start with the shortest and most common characters in our code: The { and }. They are often referred to as curly braces, and in C#, they mark the beginning and end of a logical block of code. The curly braces are used in lots of other languages, including C++, Java, JavaScript and many others. As you can see in the code, they are used to wrap several lines of code which belongs together. In later examples, it will be clearer how they are used. 

Now let's start from the beginning:

using is a keyword, highlighted with blue by the editor. The using keyword imports a namespace, and a namespace is a collection of classes. Classes brings us some sort of functionality, and when working with an advanced IDE like Visual C# Express, it will usually create parts of the trivial code for us. In this case, it created a class for us, and imported the namespaces which is required or expected to be used commonly. In this case, 3 namespaces are imported for us, each containing lots of useful classes. For instance, we use the Console class, which is a part of the System namespace. 

As you can see, we even get our own namespace:

The namespace ConsoleApplication1 is now the main namespace for this application, and new classes will be a part of it by default. Obviously, you can change this, and create classes in another namespace. In that case, you will have to import this new namespace to use it in your application, with the using statement, like any other namespace. 

Next, we define our class. Since C# is truly an Object Oriented language, every line of code that actually does something, is wrapped inside a class. In the case, the class is simply called Program:

We can have more classes, even in the same file. For now, we only need one class. A class can contain several variables, properties and methods, concepts we will go deeper into later on. For now, all you need to know is that our current class only contains one method and nothing else. It's declared like this:

This line is probably the most complicated one in this example, so let's split it up a bit. The first word is static. The static keyword tells us that this method should be accesible without instantiating the class, but more about this in our chapter about classes. 

The next keyword is void, and tells us what this method should return. For instance, int could be an integer or a string of text, but in this case, we don't want our method to return anything, or void, which is the same as no type. 

The next word is Main, which is simply the name of our method. This method is the so-called entry-point of our application, that is, the first piece of code to be executed, and in our example, the only piece to be executed. 

Now, after the name of a method, a set of arguments can be specified within a set of parentheses. In our example, our method takes only one argument, called args. The type of the argument is a string, or to be more precise, an array of strings, but more on that later. If you think about it, this makes perfect sense, since Windows applications can always be called with an optinal set of arguments. These arguments will be passed as text strings to our main method. 

And that's it. You should now have a basic understanding of our first C# application, as well as the basic principles of what makes a console application work.