Hello World: Your First C# Program
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Hello World is traditionally the first program a learner will write. It's simple, basic, and also verifies that your environment is set up correctly. It's important to start somewhere, so we'll start here.
Why is this important to learn about?
This is the basic introduction to a language; specifically: C#. If you don't start with a good foundation, you risk learning bad habits that are almost impossible to break later.
Definitions of terms used.
Note: All examples were created using Visual Studio 2010, targetting the .NET Framework 4.0. We'll do our best to point out anything that might not work in older versions.
Hello World
Getting Started
We'll start at the very beginning. Open up Visual Studio. Again, I'm using Visual Studio 2010, but for a program like this, any version all the way back to Visual Studio.NET will work, including Express Editions (the freeware versions).
Here's what you should see (or something similar to it).
Let's make a new project. There's a button on the toolbar, or we can do this through the File menu. Choose a Windows Console Application, and name it HelloWorld.
It should take a moment or two to create the project for you. It should finish, and then open up a file named Program.cs with some code already added.
This is your basic console application template. If you ran this code right now, the console would appear and quickly disappear, since you haven't written anything. That's what a basic console application will do: start and finish. You have to provide all the stuff in between.
The Default Template Explained
So, before we write any code, let's take a look at each part that was already included. The first line is:
using System;
This is what is known as a using directive. The .NET Framework is broken up across several libraries into what are called namespaces. These namespaces are used for logical grouping of types. For instance, you'll find tools to write and read from files in System.IO, or tools for network communication in System.Net.
Using directives tell the compiler to look in these namespaces to find the tools we're using. We don't have to use these using directives. We could fully qualify all the types we use (it's just plainly inconvenient). The most important one for this example: System. It contains basic tools, classes, and exceptions. In this example, we'll use it to write text to the console.
The other using directives are not important for this example. They're included automatically because they are frequently used, but we don't care about them at the moment.
Next, we see a namespace declared. As we mentioned before, these are to create logical groupings of scopes. You'll notice that this namespace is the same name as our project: HelloWorld.
Next, the line class Program. This line begins our class definition. Classes are a construct that can contain properties and methods. We'll learn more about them later in the series. For now, just understand that our program exists inside this class named Program.
Next, the line static void Main(string[] args). This is what is known as the Main method. This is the entry point of the application; this is where the program starts when it is run. Methods (also known as functions) are effectively blocks of code created to do something. You can create more than one, and call them repeatedly. Main is a special one. When the computer runs the program, Main is where it always starts.
After that, all there are are closing braces. Braces in C# define scopes. We'll cover scope more deeply in later tutorials. For now, notice how for every open brace {, there's a closing brace }. And notice that the braces correspond with the constructs we've already discussed: methods, classes and namespaces. There are several others, but again, we'll cover them more deeply in later tutorials.
Adding Our Own Code!
C# is a fairly semantic language, and the "Hello World" program is a great example of this. Let's think what we want to do. We want to write a line of text to the console. To do that, we use Console.WriteLine().
Add this in the Main method, in between the braces:
Console.WriteLine("Hello World");
Now you have a complete program. If you run it now, it will print what's in the quotation marks out to the console. Let's run it now. Press F5, or click the green right-facing triangle on the toolbar. You can also go to the Debug menu and choose "Start Debugging".
What happened?! The console popped up and disappeared too quickly to read! Why did it do that? Well, it's just the nature of the windows console. If a program that runs in the console opened the console, the console will be closed when the program exits. And our program exits immediately after it prints. So the console exits too, faster than we can read it.
There's a simple way to solve this. We add one more line of code: one that waits for user input:
Console.ReadKey();
That code takes in the next key that the user presses. It "blocks" the program until that key is pressed. So when it gets to that line, everything stops and waits. Which works perfectly for our purposes. Run the program again. This time, the console will appear and wait for you to push a key before it goes away.
That's it! You've just written your first C# application. Not too hard, right? Visual Studio does most of the work for you.
On that note, I'd like to start now impressing upon you the importance of trusting Visual Studio's tools. This is not a low level language with tools that don't help much. Visual Studio is a very well designed IDE, with excellent auto-completion features (known as IntelliSense) and great error checking. If you're trying to use a name and IntelliSense is trying to correct it into something else, either you've misspelled it, or there's a compilation error preventing it from finding what you want. If there's a red squiggly line under some code, it means that there's an error there or somewhere near it. Trust your tools, and your work will go much faster and easier. Don't try to fight against it.
In Conclusion
To wrap all this up, don't be afraid of trying stuff. Change the code a bit, and see what happens. See what happens when you add more WriteLines. Experiment. Read the MSDN, and the rest of our tutorials. Look up more tutorials. Learning how to program is great fun!
See all the C# Learning Series tutorials here!
This post has been edited by insertAlias: 22 March 2011 - 09:52 PM
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