Programming C#, Third Edition

Chapter 2. Getting Started: “Hello World”

It is a time-honored tradition to start a programming book with a “Hello World” program. In this chapter, we create, compile, and run a simple "Hello World” program written in C#. The analysis of this brief program will introduce key features of the C# language.

Example 2-1 illustrates the fundamental elements of a very elementary C# program.

Example 2-1. A simple “Hello World” program in C#

class Hello
{
    static void Main( )
    {
        // Use the system console object
        System.Console.WriteLine("Hello World");
    }
}

Compiling and running this code displays the words “Hello World” at the console. Let’s take a closer look at this simple program.

Classes, Objects, and Types

The essence of object-oriented programming is the creation of new types. A type represents a thing. Sometimes the thing is abstract, such as a data table or a thread; sometimes it is more tangible, such as a button in a window. A type defines the thing’s general properties and behaviors.

If your program uses three instances of a button type in a window—say, an OK, a Cancel, and a Help button—each instance will share certain properties and behaviors. Each, for example, will have a size (though it might differ from that of its companions), a position (though again, it will almost certainly differ in its position from the others), and a text label (e.g., “OK,” “Cancel,” and “Help”). Likewise, all three buttons will have common behaviors, such as the ability to be drawn, activated, pressed, ...