Introduction to C# Applications

This chapter is from the book

C# 2010 for Programmers, 4th Edition

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This chapter is from the book

This chapter is from the book 

C# 2010 for Programmers, 4th Edition

Learn More Buy

3.3 Creating a Simple Application in Visual C# Express

Now that we have presented our first console application (Fig. 3.1), we provide a step-by-step explanation of how to compile and execute it using Visual C# Express.

Creating the Console Application

After opening Visual C# 2010Express, select File > New Project... to display the New Project dialog (Fig. 3.3), then select the Console Application template. In the dialog's Name field, type Welcome1. Click OK to create the project. The IDE now contains the open console application, as shown in Fig. 3.4. The editor window already contains some code provided by the IDE. Some of this code is similar to that of Fig. 3.1. Some is not, and uses features that we have not yet discussed. The IDE inserts this extra code to help organize the application and to provide access to some common classes in the .NET Framework Class Library—at this point in the book, this code is neither required nor relevant to the discussion of this application; delete all of it.

Fig. 3.3 Creating a Console Application with the New Project dialog.

Fig. 3.4 IDE with an open console application.

The code coloring scheme used by the IDE is called syntax-color highlighting and helps you visually differentiate application elements. For example, keywords appear in blue, and comments appear in green. When present, comments are green. In this black-and-white book, we syntax-shade our code similarly—bold for keywords, gray for comments, bold gray for literals and constants, and black for other text. One example of a literal is the string passed to Console.WriteLine in line 10 of Fig. 3.1. You can customize the colors shown in the code editor by selecting Tools > Options.... This displays the Options dialog. Then expand the Environment node and select Fonts and Colors. Here you can change the colors for various code elements.

Modifying the Editor Settings to Display Line Numbers

Visual C# Express provides many ways to personalize your coding experience. In this step, you'll change the settings so that your code matches that of this book. To have the IDE display line numbers, select Tools > Options.... In the dialog that appears (Fig. 3.5), click the Show all settings checkbox on the lower left of the dialog, then expand the Text Editor node in the left pane and select All Languages. On the right, check the Line numbers checkbox. Keep the Options dialog open.

Fig. 3.5 Modifying the IDE settings.

Setting Code Indentation to Three Spaces per Indent

In the Options dialog that you opened in the previous step (Fig. 3.5), expand the C# node in the left pane and select Tabs. Make sure that the option Insert spaces is selected. Enter 3 for both the Tab size and Indent size fields. Any new code you add will now use three spaces for each level of indentation. Click OK to save your settings, close the dialog and return to the editor window.

Changing the Name of the Application File

For applications we create in this book, we change the default name of the application file (i.e., Program.cs) to a more descriptive name. To rename the file, click Program.cs in the Solution Explorer window. This displays the application file's properties in the Properties window (Fig. 3.6). Change the File Name property to Welcome1.cs.

Fig. 3.6 Renaming the program file in the Properties window.

Writing Code and Using IntelliSense

In the editor window (Fig. 3.4), type the code from Fig. 3.1. As you begin typing (in line 10) the class name class name Console, an IntelliSense window containing a scrollbar is displayed as shown in Fig. 3.7. This IDE feature lists a class's members, which include method names. As you type characters, Visual C# Express highlights the first member that matches all the characters typed, then displays a tool tip containing a description of that member. You can either type the complete item name (e.g., Console), double click the item name in the member list or press the Tab key to complete the name. Once the complete name is provided, the IntelliSense window closes. While the IntelliSense window is displayed, pressing the Ctrl key makes the window transparent so you can see the code behind the window.

Fig. 3.7 feature of Visual C# Express.

When you type the dot (.) after Console, the IntelliSense window reappears and shows only the members of class Console that can be used on the right side of the dot (Fig. 3.7, part 1). When you type the open parenthesis character, (, after Console.WriteLine, the Parameter Info window is displayed (Fig. 3.8). This window contains information about the method's parameters. As you'll learn in Chapter 7, there can be several versions of a method.

That is, a class can define several methods that have the same name, as long as they have different numbers and/or types of parameters—a concept known as overloaded methods. These methods normally all perform similar tasks. The Parameter Info window indicates how many versions of the selected method are available and provides up and down arrows for scrolling through the different versions. For example, there are 19 versions of the WriteLine method—we use one of these 19 versions in our application. The Parameter Info window is one of many features provided by the IDE to facilitate application development. In the next several chapters, you'll learn more about the information displayed in these windows. The Parameter Info window is especially helpful when you want to see the different ways in which a method can be used. From the code in Fig. 3.1, we already know that we intend to display one string with WriteLine, so, because you know exactly which version of WriteLine you want to use, you can simply close the Parameter Info window by pressing the Esc key.

Fig. 3.8 Parameter Info window.

Saving the Application

Select File > Save All to display the Save Project dialog (Fig. 3.9). In the Location textbox, specify the directory where you want to save this project. We chose the MyProjects directory on the C: drive. Select the Create directory for solution checkbox and click Save.

Fig. 3.9 Save Project dialog.

Compiling and Running the Application

You're now ready to compile and execute your application. Depending on its type, the compiler may compile the code into files with a .exe (executable) extension, a .dll (dynamically linked library) extension or one of several other extensions. Such files are called assemblies and are the packaging units for compiled C# code. These assemblies contain the Microsoft Intermediate Language (MSIL) code for the application.

To compile the application, select Debug > Build Solution. If the application contains no syntax errors, this will compile your application and build it into an executable file (named Welcome1.exe, in one of the project's subdirectories). To execute it, type Ctrl + F5, which invokes the Main method (Fig. 3.1). (If you attempt to run the application before building it, the IDE will build the application first, then run it only if there are no compilation errors.) The statement in line 10 of Main displays Welcome to C# Programming!. Figure 3.10 shows the results of executing this application, displayed in a console (Command Prompt) window. Leave the application's project open in Visual C# Express; we'll go back to it later in this section. [Note: Many environments show Command Prompt windows with black backgrounds and white text. We adjusted these settings in our environment to make our screen captures more readable.]

Fig. 3.10 Executing the application shown in Fig. 3.1.

Error-Prevention Tip 3.4

When learning how to program, sometimes it's helpful to "break" a working application so you can familiarize yourself with the compiler's syntax-error messages. Try removing a semicolon or brace from the code of Fig. 3.1, then recompiling the application to see the error messages generated by the omission.

Running the Application from the Command Prompt

As we mentioned at the beginning of the chapter, you can execute applications outside the IDE in a Command Prompt. This is useful when you simply want to run an application rather than open it for modification. To open the Command Prompt, select Start > All Programs > Accessories > Command Prompt. The window (Fig. 3.11) displays copyright information, followed by a prompt that indicates the current directory. By default, the prompt specifies the current user's directory on the local machine (in our case, C:\Users\paul). On your machine, the folder name paul will be replaced with your user-name.

Fig. 3.11 Command Prompt window when it's initially opened.

Enter the command cd (which stands for "change directory"), followed by the /d flag (to change drives if necessary), then the directory where the application's .exe file is located (i.e., your application's bin\Debug or bin\Release directory). For example, the command

cd /d C:\MyProjects\Welcome1\Welcome1\bin\Release

(Fig. 3.12) changes the current directory, to the Welcome1 application's Release directory on the C: drive. The next prompt displays the new directory. After changing to the proper directory, you can run the application by entering the name of the .exe file—Welcome1. The application will run to completion, then the prompt will display again, awaiting the next command. To close the Command Prompt, type exit (Fig. 3.12) and press Enter.

Fig. 3.12 Executing the application shown in Command Prompt from a Command Prompt window.

Visual C# 2010 Express maintains a Debug and a Release directory in each project's bin directory. The Debug directory contains a version of the application that can be used with the debugger (see Appendix G, Using the Visual C# 2010 Debugger). The Release directory contains an optimized version that you could provide to your clients. In the complete Visual Studio 2008, you can select the specific version you wish to build from the Solution Configurations drop-down list in the toolbars at the top of the IDE. The default is the Release version. The Debug version is created if you run the program with Debug > Start Debugging.

Syntax Errors, Error Messages and the Error List Window

Go back to the application in Visual C# Express. As you type code, the IDE responds either by applying syntax-color highlighting or by generating a syntax error, which indicates a violation of Visual C#'s rules for creating correct applications (i.e., one or more statements are not written correctly). Syntax errors occur for various reasons, such as missing parentheses and misspelled keywords.

When a syntax error occurs, the IDE underlines the error in red and provides a description of it in the Error List window (Fig. 3.13). If the Error List window is not visible in the IDE, select View > Error List to display it. In Figure 3.13, we intentionally omitted the comma between "Welcome to" and "C# Programming!" in line 10. The first error is simply indicating that line 10 is not a valid statement. The second error indicates that a right parenthesis is expected at character position 51 in the statement, because the compiler is confused by the unmatched left parenthesis from earlier in line 10. The third error has the text "Invalid expression term ')'", because the compiler thinks the closing right parenthesis should have appeared earlier in the line. The fourth error has the text "; expected", because the prior errors make the compiler think that the statement should have been terminated with a semicolon earlier in the line. Although we deleted only one comma in line 10, this caused the compiler to misinterpret several items in this line and to generate four error messages. You can double click an error message in the Error List to jump to the place in the code that caused the error.

Error-Prevention Tip 3.5

One syntax error can lead to multiple entries in the Error List window. Each error that you address could eliminate several subsequent error messages when you recompile your application. So when you see an error you know how to fix, correct it and recompile—this may make several other errors disappear.

Fig. 3.13 Syntax errors indicated by the IDE.