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PART I
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NOTE Although the preceding instructions are sufficient to compile and run the programs in this
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book, if you will be using the Visual Studio IDE for your main work environment, you should become familiar with all of its capabilities and features It is a very powerful development environment that helps make large projects manageable The IDE also provides a way of organizing the files and resources associated with a project It is worth the time and effort that you spend to become proficient at running Visual Studio
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The First Sample Program, Line by Line
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Although Examplecs is quite short, it includes several key features that are common to all C# programs Let s closely examine each part of the program, beginning with its name The name of a C# program is arbitrary Unlike some computer languages (most notably, Java) in which the name of a program file is very important, this is not the case for C# You were told to call the sample program Examplecs so that the instructions for compiling and running the program would apply, but as far as C# is concerned, you could have called the file by another name For example, the preceding sample program could have been called Samplecs, Testcs, or even Xcs By convention, C# programs use the cs file extension, and this is a convention that you should follow Also, many programmers call a file by the name of the principal class defined within the file This is why the filename Examplecs was chosen Since the names of C# programs are arbitrary, names won t be specified for most of the sample programs in this book Just use names of your own choosing The program begins with the following lines:
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/* This is a simple C# program Call this program Examplecs */
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This is a comment Like most other programming languages, C# lets you enter a remark into a program s source file The contents of a comment are ignored by the compiler Instead, a comment describes or explains the operation of the program to anyone who is reading its source code In this case, the comment describes the program and reminds you to call the source file Examplecs Of course, in real applications, comments generally explain how some part of the program works or what a specific feature does C# supports three styles of comments The one shown at the top of the program is called a multiline comment This type of comment must begin with /* and end with */ Anything between these two comment symbols is ignored by the compiler As the name suggests, a multiline comment can be several lines long The next line in the program is
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using System;
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Part I:
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The C# Language
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This line indicates that the program is using the System namespace In C#, a namespace defines a declarative region Although we will examine namespaces in detail later in this book, a brief description is useful now Through the use of namespaces, it is possible to keep one set of names separate from another In essence, names declared in one namespace will not conflict with names declared in a different namespace The namespace used by the program is System, which is the namespace reserved for items associated with the NET Framework class library, which is the library used by C# The using keyword simply states that the program is using the names in the given namespace (As a point of interest, it is also possible to create your own namespaces, which is especially helpful for large projects) The next line of code in the program is shown here:
class Example {
This line uses the keyword class to declare that a new class is being defined As mentioned, the class is C# s basic unit of encapsulation Example is the name of the class The class definition begins with the opening curly brace ({) and ends with the closing curly brace (}) The elements between the two braces are members of the class For the moment, don t worry too much about the details of a class except to note that in C#, most program activity occurs within one The next line in the program is the single-line comment, shown here:
// A C# program begins with a call to Main()
This is the second type of comment supported by C# A single-line comment begins with a // and ends at the end of the line Although styles vary, it is not uncommon for programmers to use multiline comments for longer remarks and single-line comments for brief, line-byline descriptions (The third type of comment supported by C# aids in the creation of documentation and is described in the Appendix) The next line of code is shown here:
static void Main() {
This line begins the Main( ) method As mentioned earlier, in C#, a subroutine is called a method As the comment preceding it suggests, this is the line at which the program will begin executing All C# applications begin execution by calling Main( ) The complete meaning of each part of this line cannot be given now, since it involves a detailed understanding of several other C# features However, since many of the examples in this book will use this line of code, we will take a brief look at it here The line begins with the keyword static A method that is modified by static can be called before an object of its class has been created This is necessary because Main( ) is called at program startup The keyword void indicates that Main( ) does not return a value As you will see, methods can also return values The empty parentheses that follow Main indicate that no information is passed to Main( ) Although it is possible to pass information into Main( ), none is passed in this example The last character on the line is the { This signals the start of Main( ) s body All of the code that comprises a method will occur between the method s opening curly brace and its closing curly brace The next line of code is shown here Notice that it occurs inside Main( )
ConsoleWriteLine("A simple C# program");
2:
An Overview of C#
This line outputs the string A simple C# program followed by a new line on the screen Output is actually accomplished by the built-in method WriteLine( ) In this case, WriteLine( ) displays the string that is passed to it Information that is passed to a method is called an argument In addition to strings, WriteLine( ) can be used to display other types of information The line begins with Console, which is the name of a predefined class that supports console I/O By connecting Console with WriteLine( ), you are telling the compiler that WriteLine( ) is a member of the Console class The fact that C# uses an object to define console output is further evidence of its object-oriented nature Notice that the WriteLine( ) statement ends with a semicolon, as does the using System statement earlier in the program In general, statements in C# end with a semicolon The exception to this rule are blocks, which begin with a { and end with a } This is why those lines in the program don t end with a semicolon Blocks provide a mechanism for grouping statements and are discussed later in this chapter The first } in the program ends Main( ), and the last } ends the Example class definition One last point: C# is case-sensitive Forgetting this can cause serious problems For example, if you accidentally type main instead of Main, or writeline instead of WriteLine, the preceding program will be incorrect Furthermore, although the C# compiler will compile classes that do not contain a Main( ) method, it has no way to execute them So, had you mistyped Main, you would see an error message that states that Exampleexe does not have an entry point defined
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