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130 Control Structures: Part 1 Chapter 4 5. Examine the results of the ASimpleProgram_Load method. Notice that the text in the label looks the same in Design mode as it did in Fig. 4.22. Note also that the property window still displays the value VisualC# .NET as the label s Text property and that the IDE generated code has not changed either. Select Build > Build then Debug > Start to run the program. Once the form is displayed, the text in the label reflects the property assignment in ASimpleProgram_Load (Fig. 4.24). 6. Terminate program execution. Click the close button to terminate program execution. Once again, notice that both the label and the label s Text property contain the text Visual C#.NET. The IDE generated code also contains the text VisualC#. NET, which is assigned to the label s Text property. In this chapter, we introduced program building blocks called control structures. We also discussed aspects of Windows application programming. In Chapter 5, Control Structures: Part 2, we continue our discussion of control structures by presenting additional selection and repetition structures. In addition, we also build upon the Windows application concepts presented in this chapter by creating a richer Windows application. SUMMARY Executing a series of actions in a specific order can solve many computing problems. A procedure for solving a problem in terms of the actions to execute and the order in which these actions execute is an algorithm. Program control specifies the order in which statements execute in a computer program. Pseudocode is an artificial and informal language that helps programmers develop algorithms and think out a program during the program design process. C# code corresponds closely to pseudocode. This is a property of pseudocode that makes it a useful program development tool. Normally, statements in a program execute one after the other in the order in which they appear. This is called sequential execution. Fig. 4.24 Changing a property value at runtime.
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Chapter 4 Control Structures: Part 1 129 Text property value Fig. 4.22 New Text property value reflected in design mode. 4. Change the label s Text property at runtime. In the previous steps, we set properties at design time. Often, however, it is necessary to modify a property while a program is running. For example, to display the result of a calculation, a label s text can be assigned a string containing the result. In console applications, such code is located in Main. In Windows applications, we must create a method that executes when the form is loaded into memory during program execution. Like Main, this method is invoked when the program is run. Double-clicking the form in design view adds a method named ASimpleProgram_Load to the class (Fig. 4.23). The cursor is placed in the body of the ASimpleProgram_Load method definition. Notice that ASimpleProgram_Load is not part of the Windows Form Designer generated code. Add the statement welcomeLabel.Text=”C#”; in the body of the method definition (Fig. 4.23). In C#, properties are accessed by placing the property name (i.e., Text) after the object name (i.e., welcomeLabel), separated by the dot operator. This syntax is similar to that used when accessing object methods. Notice that the IntelliSense feature displays the Text property in the member list after the class name and dot operator have been typed (Fig. 4.29). In Chapter 8, Object-Based Programming, we discuss how programmers can create their own properties. ASimpleProgram_Load method Fig. 4.23 Method FrmASimpleProgram_Load.
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128 Control Structures: Part 1 Chapter 4 2. Examine the changes in the code view. Switch to code view and examine the code. Notice that the label s Text property is now assigned the text that we entered in the Properties window (Fig. 4.20). When a property is changed in design mode, the Windows Form Designer updates the appropriate line of code in the class to reflect the new value. 3. Modifying a property value in code view. In the code view editor, locate the three lines of comments indicating the initialization for welcomeLabel and change the string assigned to this.welcomeLabel.Text from Deitel to VisualC#.NET (Fig. 4.21). Now, switch to design mode. The label now displays the updated text, and the Properties window for welcomeLabel displays the new Text value (Fig. 4.22). [Note: Property values should not be set using the techniques presented in this step. Here, we modify the property value in the IDE generated code only as a demonstration of the relationship between program code and the Windows Form Designer.] Fig. 4.20 Windows Form Designer generated code reflecting new property values. Text property Fig. 4.21 Changing a property in the code view editor.
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Chapter 4 Control Structures: Part 1 127 Property initializations Click here for Click here for for welcomeLabel design view code view Fig. 4.18 Code generated by the IDE for welcomeLabel. The values assigned to the properties are based on the values in the Properties window. We now demonstrate how the IDE updates the Windows Form Designer generated code it generates when a property value in the Properties window changes. During this process, we must switch between code view and design view. To switch views, select the corresponding tabs Form1.cs* for code view and Form1.cs* [Design] for design view. Alternatively, the programmer can select View > Code or View > Designer. Perform the following steps: 1. Modify the label control s Text property using the Properties window. Recall that properties can be changed in design view by clicking a form or control to select it, then modifying the appropriate property in the Properties window. Change the Text property of the label to Deitel (Fig. 4.19). Text property Fig. 4.19 Using the Properties window to set a property value.
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