C#. net Basic Tutor - skills to develop....

[arun]

There are basic elements that all C# executable programs have and that's what we'll concentrate on for this first lesson, starting off with a simple C# program. After reviewing the code in Listing 1-1, I'll explain the basic concepts that will follow for all C# programs we will write throughout this tutorial. Please see Listing 1-1 to view this first program.

Warning: C# is case-sensitive.
Listing 1-1. A Simple Welcome Program: Welcome.cs

// Namespace Declaration
using System;

// Program start class
class WelcomeCSS
{
    // Main begins program execution.
    static void Main()
    {
        // Write to console
        Console.WriteLine("Welcome to the C# Station Tutorial!");
    }
}

The program in Listing 1-1 has 4 primary elements, a namespace declaration, a class, a Main method, and a program statement. It can be compiled with the following command line:
csc.exe Welcome.cs



Get Setup Instructions For How to Run this Program

This produces a file named Welcome.exe, which can then be executed. Other programs can be compiled similarly by substituting their file name instead of Welcome.cs. For more help about command line options, type "csc -help" on the command line. The file name and the class name can be totally different.

Note for VS.NET Users: The screen will run and close quickly when launching this program from Visual Studio .NET.; To prevent this add the following code as the last line in the Main method:

// keep screen from going away
// when run from VS.NET
Console.ReadLine();

Note: The command-line is a window that allows you to run commands and programs by typing the text in manually. It is often refered to as the DOS prompt, which was the operating system people used years ago, before Windows. The .NET Framework SDK, which is free, uses mostly command line tools. Therefore, I wrote this tutorial so that anyone would be able to use it. Do a search through Windows Explorer for "csc.exe", which is the C# compiler. When you know its location, add that location to your Windows path. If you can't figure out how to add something to your path, get a friend to help you. With all the different versions of Windows available, I don't have the time in this tutorial, which is about C# language programming, to show you how to use your operating system. Then open the command window by going to the Windows Start menu, selecting Run, and typing cmd.exe.

The first thing you should be aware of is that C# is case-sensitive. The word "Main" is not the same as its lower case spelling, "main". They are different identifiers. If you are coming from a language that is not case sensitive, this will trip you up several times until you become accustomed to it.

The namespace declaration, using System;, indicates that you are referencing the System namespace. Namespaces contain groups of code that can be called upon by C# programs. With the using System; declaration, you are telling your program that it can reference the code in the System namespace without pre-pending the word System to every reference. I'll discuss this in more detail in Lesson 06: Namespaces, which is dedicated specifically to namespaces.

The class declaration, class WelcomeCSS, contains the data and method definitions that your program uses to execute. A class is one of a few different types of elements your program can use to describe objects, such as structs, interfaces , delegates, and enums, which will be discussed in more detail in Lesson 12: Structs, Lesson 13: Interfaces, Lesson 14: Delegates, and Lesson 17: Enums, respectively. This particular class has no data, but it does have one method. This method defines the behavior of this class (or what it is capable of doing). I'll discuss classes more in Lesson 07: Introduction to Classes. We'll be covering a lot of information about classes throughout this tutorial.

The one method within the WelcomeCSS class tells what this class will do when executed. The method name, Main, is reserved for the starting point of a program. Main is often called the "entry point" and if you ever receive a compiler error message saying that it can't find the entry point, it means that you tried to compile an executable program without a Main method.

A static modifier preceeds the word Main, meaning that this method works in this specific class only, rather than an instance of the class. This is necessary, because when a program begins, no object instances exist. I'll tell you more about classes, objects, and instances in Lesson 07: Introduction to Classes.

Every method must have a return type. In this case it is void, which means that Main does not return a value. Every method also has a parameter list following its name with zero or more parameters between parenthesis. For simplicity, we did not add parameters to Main. Later in this lesson you'll see what type of parameter the Main method can have. You'll learn more about methods in Lesson 05: Methods.

The Main method specifies its behavior with the Console.WriteLine(...) statement. Console is a class in the System namespace. WriteLine(...) is a method in the Console class. We use the ".", dot, operator to separate subordinate program elements. Note that we could also write this statement as System.Console.WriteLine(...). This follows the pattern "namespace.class.method" as a fully qualified statement. Had we left out the using System declaration at the top of the program, it would have been mandatory for us to use the fully qualified form System.Console.WriteLine(...). This statement is what causes the string, "Welcome to the C# Station Tutorial!" to print on the console screen.

Observe that comments are marked with "//". These are single line comments, meaning that they are valid until the end-of-line. If you wish to span multiple lines with a comment, begin with "/*" and end with "*/". Everything in between is part of the comment. You can place a single line comment within a multi-line comment. However, you can't put multi-line comments within a multi-line comment. Comments are ignored when your program compiles. They are there to document what your program does in plain English (or the native language you speak with every day).

All statements end with a ";", semi-colon. Classes and methods begin with "{", left curly brace, and end with a "}", right curly brace. Any statements within and including "{" and "}" define a block. Blocks define scope (or lifetime and visibility) of program elements.
Accepting Command-Line Input

In the previous example, you simply ran the program and it produced output.  However, many programs are written to accept command-line input. This makes it easier to write automated scripts that can invoke your program and pass information to it. If you look at many of the programs, including Windows OS utilities, that you use everyday; most of them have some type of command-line interface.  For example, if you type Notepad.exe MyFile.txt (assuming the file exists), then the Notepad program will open your MyFile.txt file so you can begin editing it. You can make your programs accept command-line input also, as shown in Listing 1-2, which shows a program that accepts a name from the command line and writes it to the console.