Hello, World! – again

In 15 Exercises for Learning a new Programming Language, Prashant Mhatre kicks off with:

First of all, get familiar with Compiler, compiler option, editor shortcuts or integrated development environment (IDE). Start with a simple ‘Hello World’ program. Compile it. Use basic functionalities of debugger like setting break points, printing variable values, moving to the next or specific position, stopping debugger etc.

Let’s jump straight into the code first.

Here’s the most basic “Hello World” in C#:

class MainClass
{
    static void Main()
    {
        System.Console.WriteLine("Hello, World!");
    }
}

This looks a little different to the way it’s presented in most tutorials, but I’ll get to that in a minute.

The first thing to notice here is the MainClass class.  In general terms, the only things that can be at the global level of a C# source file are certain type declarations, namespace and alias declarations, and using-namespace-directives.  This means that the entry point of the program (the main() function in C) must actually be a method of a class.  The name of the class here is not important. 

The Main() method must be a static member.  A static member operates without reference to a specific class instance, and exists independent of class instantiation.  More on this at a later time.

The Main() method, like in C, can be declared to return void or int, and may take command-line arguments as an array of strings, like this:

static int Main(string[] args) { ... }

The last thing to notice about “Hello World” is the line that does the actual work. In this line, WriteLine is a method of the Console class which is a member of the System namespace.  In C#, classes, and other types, are organised into a namespace hierarchy.  In the code above the MainClass class is in the global namespace.  A program is able to declare its own namespaces.

The other thing we can do is tell the compiler which namespaces we want to use the members of, with a using directive.  So “Hello World” can also be written:

using System;

class MainClass
{
    static void Main()
    {
        Console.WriteLine("Hello, World!");
    }
}

This is the form usually seen in C# tutorials.  The first line says that we want to be able to use the members of the System namespace without using the fully qualified name.  Thus, in the program we are now able to use the Console class directly.

Now that we’ve got some code we need a compiler so we can turn it into an executable program.  The .NET framework provides a C# compiler called csc.exe.  On my computer with version 4.0 of the .NET framework, the compiler is at C:\Windows\Microsoft.NET\Framework\v4.0.30319\csc.exe.  I added the folder to my PATH to make things easier.

Save the above code in a file called HelloWorld.cs and then do:

csc.exe HelloWorld.cs

This will create HelloWorld.exe which will write the familiar greeting to the console.  “csc.exe /?” will give the list of options available when running the compiler.

Of course, an easier way to do things is to use an IDE, and for the price (free) you really can’t go past Microsoft Visual C# Express.  I won’t go into all the options and debugging methods here – I’ll leave that as an exercise for the reader.  Suffice to say that if you’re at all familiar with Microsoft’s Visual Studio family of products you’ll be right at home.

I think that will do it for this time.  In the next post we’ll tackle Prashant’s first exercise.