But we suggest that you limit your first database tables to a small number of fields. DYNAMIC ROSTER Students submissions are stored in a roster that indicates whether the submission is correct, how many attempts were made, and the actual code submissions from each attempt. It must be a numeric variable. 4. Check the flowchart or pseudocode for errors. is information that is passed to a function when the 13. Step 2: Practice turning the Auto Hide feature on and off for the Solution Explorer window, the Properties window, and the Toolbox. When the user edits the model name, the control modifies the BindingSource.Current object somehow, and the BindingSource raises the CurrentItemChanged event. The importance of commenting code is also discussed. Wear a coat. In the next section, we examine the controls and event handlers more closely. HTML, which stands for HyperText Markup Language, is a standardized language that describes the appearance of pages. Theater Revenue A movie theater only keeps a percentage of the revenue earned from ticket sales. 10.8 Creating Your Own Database Always design your database structure before starting to create the database in Visual Studio. Figure 3-29 Examples of default exception messages 183 184 Chapter 3 Variables and Calculations Checkpoint 3.33 What is an exception? Forms have two properties named AcceptButton and CancelButton. The Code window will open, with an empty code template for the Form1_Load event handler. The declaration indicates the name you wish to give the variable and the type of data the variable will hold. 175 176 Chapter 3 Variables and Calculations Failure Can Be Graceful Exceptions are typically thrown because of events outside the programmers control. a. Each Visual Basic application that you create is called a project. The following is a pseudocode version of the btnCalcGrossPay_Click event handler: Store Number of Hours Worked Hourly Pay Rate in the grossPay variable. Converting Celsius to Fahrenheit Create an application that converts Celsius to Fahrenheit. A variables data type determines the type of information that the variable can hold. This statement in line 6 converts the decTotal variable to a string, and assigns the result to the lblTotal controls Text property. 727 728 Chapter 11 Developing Web Applications Figure 11-21 Picnic application Design view, after inserting the TextBox controls Step 10: Insert a blank line, then on the next line insert a Label control. Step 2: On the form, create a list box as shown in Figure 5-8. When a TextBox control is created, it will be given a default name. Complete the event handler by writing the following bold code shown in lines 2 through 15. When you set AutoPostBack to True for a list-type control, users experience a short delay each time they click on the list. Easily arrange diagram components in layout such as. The flowchart in Figure 5-13 shows the logic of a posttest Do While loop. For example, compare the following statements: If decSales > 50000 Then lblMessage.Text = "You've earned a bonus!" Step 8: Click the Exit button to terminate the application. 7. Next, when you type a period, an IntelliSense list pops up showing every property and method belonging to the lblTranslation control. NumberGroupSeparator - By default, the comma (,) separates group of digits before the decimal point. 3.6 Class-Level Variables CONCEPT: Class-level variables are accessible to all procedures in a class. T F: When you lock the controls on a form, the user must enter a password before the application will run. Press the to select the highlighted data type. For example, it is evident that the btnCalcGrossPay control is a button that calculates the gross pay. Then, verify that Option Explicit and Option Strict are set to On. Add a preview text input event. You can modify the tab order by changing a controls property. 10. Figure 3-11 Project Properties page Set Option strict to On Select Compile Type Conversion Runtime Errors The following statement does not compile with Option Strict set to On: Dim intCount As Integer = "abc123" But if Option Strict has been set to Off, a program containing this statement will compile without errors. Resize a node in eight different directions. 171 172 Chapter 3 Variables and Calculations Step 7: Switch your view back to the Designer and double-click the picTenCents control. The data source to ComboBox can be set by using GridComboBoxColumn.ItemsSource property. Unlike the SQL operators, however, the LINQ operators are built into the Visual Basic language. The exceptions that may be caused by these functions and methods are also listed. The text My First Program will now appear in the forms title bar, as shown in Figure 2-5. Suppose we had stored the value &Exit in the buttons Text property. Step 1: Start Visual Studio and begin a new Visual Basic Windows Forms Application project named Guess the President. 65 66 Chapter 2 Creating Applications with Visual Basic When you are ready to run an application that you are developing, you can execute it without leaving the Visual Studio environment. You can show a list within a record in a ListBox or ComboBox. Below code, creates GridCellMultiColumnDropDownRendererExt to set AllowImmediatePopup property. Unless you are certain a variable will be assigned a value before being used in an operation, always initialize it. a. b. c. d. 12. Step 4: After you select an image file, you will see its contents displayed in the Select Resource window. If it is true, then the statements in the body of the loop are executed. Figure 5-3 Input box with default input N O T E : In most applications, the InputBox function should not be used as the primary method of input because it draws the users attention away from the applications form. Suppose an applications GUI has a Label control named lblOutput. What is the purpose of inserting comments in a program? A dataset is an in-memory copy of the data pulled from database tables. Optical devices such as the CD (compact disc) and the DVD (digital versatile disc) are also popular for data storage. (The Block Format tool is located on the left side of the formatting toolbar.) An exception is an unexpected error that occurs while a program is running, causing the program to abruptly halt. $34.95 c. 2,300 d. Twelve 3.5 Formatting Numbers and Dates Users of computer programs generally like to see numbers and dates displayed in an attractive, easy to read format. 4.1 The Decision Structure CONCEPT: The decision structure allows a programs logic to have more than one path of execution. Test when the output is zero, the zero records should be affected. Although we have shown only arrays of numbers up to this point, it is important to note that arrays often contain strings. The following example is like the previous example, but uses a DataSet instead of Airplane and Passenger classes. Web Browser Support Web pages would be easier to create if all end users ran the same Web browser. 1.3 More about Controls and Programming Its important to remember that control names must be one word. Returns a copy of a string without leading spaces. (If you mistyped something, and as a result have any syntax errors, correct them.) Heres what happens: If txtInput.Text is successfully converted to an Integer, the resulting value is assigned to the intNumber variable, and the method returns True. Step 4: Click the Calculate Average button. WARNING! Similarly, the next statement rounds upward to the nearest integer when the fractional part of the number is .5 or greater: Dim intCount As Integer = 12.5 'intCount = 13 Another narrowing conversion occurs when assigning a Double value to a variable of type Single. This window is generally used by advanced programmers. If the expression is true, a statement or group of statements is executed. You can display the GroupCaptionText based on DisplayMemberPath using GroupColumnDescription.Converter property. A PictureBox control can have a Click event handler that responds when the user clicks the control at run time. Heads or Tails In the student sample programs that accompany this book, you will find a folder named Images\Coins that contains images showing the heads and tails sides of a coin. When a button has the focus, pressing the key executes the buttons Click event handler. How would i go about doing this? On modern operating systems such as Windows, most of the programs that people use have a graphical user interface, or GUI (pronounced gooey). Special programming techniques, called saving state, are available to overcome this challenge. We will permit the store manager to display and filter the rental history list by choosing either a customer name or a date range. For instructors, a comprehensive gradebook tracks correct and incorrect answers and stores the code inputted by students for review. 11.11 What happens the first time you run a Web application in Debug mode? T F: GroupBox and Label controls have a TabIndex property, but they are skipped in the tab order. Before doing any work with the elements of a string array, you must store values in them, even if the values are empty strings. CheckBoxList* ListBox DropDownList (similar to ComboBox control) Image (similar to PictureBox control) Calendar* HyperLink* Button ImageButton LinkButton TextBox Label RadioButton RadioButtonList* CheckBox Web controls have similar properties to their Windows Forms counterparts. Notice that the first step in the flowchart is to set the accumulator variable to 0. The WPF Diagram control has predefined alignment commands to align the selected objects nodes and connectors to the selection boundary. Aggregates for column values can be easily displayed using the aggregate feature. Change its name to lstYears. If the expression converts to a value outside the range of a Double, or is not a numeric value, a runtime error is generated. Also notice the statement that caused the error (line 8 in the previously shown code). The second problem occurs if this number is used in other calculations throughout the program and must be changed periodically. Microsoft has ended support for older versions of IE. Then, create an application that has a Label and two buttons on a form. Else statement Private Sub btnCalculate_Click() Handles btnCalculate.Click ' Variables to hold scores and the average score Dim dblScore1 As Double Dim dblScore2 As Double Dim dblScore3 As Double Dim dblAverage As Double 4.3 The IfThenElse Statement ' Constants Const NUM_SCORES As Integer = 3 Const dblHIGH_SCORE As Double = 95.0 Try ' Copy the TextBox scores into the variables. a. dblResult = 6 + 3 * 5 b. dblResult = 12 / 2 4 c. dblResult = 2 + 7 * 3 6 d. dblResult = (2 + 4) * 3 e. dblResult = 10 \ 3 f. dblResult = 6 2 3.13 What value will be stored in intResult after each statement executes? When an exception occurs, programmers commonly say an exception was thrown. If the output is not correct, you know there is a logic error somewhere in your code. The Items.Remove and Items.RemoveAt Methods The Items.Remove and Items.RemoveAt methods both remove one item from a list boxs Items property. The TextAlign property lets you position the text to the left or right of the box. In the third statement, the TrimEnd method is called. If the BMI value is greater than 25, the person is considered to be overweight. (Alternatively, you button.) 1.12 What is the default name given to the first TextBox control created in an application? These terms do not mean the same thing, but they are sometimes used interchangeably. Click the Calculate button. For our first example, we will show how to create a simple database to keep track of information about commercial films. Shows the student how to convert a mathematical expression into a Visual Basic programming statement. a. b. c. d. 5. Step 2: Open Form1 in design mode and double-click the Enter Sales button. Then the Not operator is applied to that value. If the expression dblX = 0 is true, then we know that the compound expression is true, so the function call can be skipped. lblInfo.Text = txtInput.Text The following statement shows another example. A description of each window follows: The Autos window displays a list of the variables appearing in the current statement, the three statements before, and the three statements after the current statement. Figure 3-12 A function receives input and produces a single output Input(s) Function Output When we send a piece of data as input to a function, we typically say that we are passing the data as an argument. T F: In the Code window, Visual Studio examines each statement as you type it, and reports any syntax errors that are found. No further action will be taken. Software reliability is particularly hard to guarantee when users have lots of choices. 1 2 3 4 5 6 7 Dim intNumber As Integer If Integer.TryParse(txtInput.Text, intNumber) Then lblResult.Text = "The value is " + intNumber Else lblResult.Text = "Cannot convert to an integer" End If The purpose of this code snippet is to convert the value of txtInputs Text property to an Integer and assign that value to the intNumber variable, which is declared in line 1. 119 120 Chapter 2 Creating Applications with Visual Basic Programming Challenges 1. The value given after the = sign is the value of the constant throughout the programs execution. This statement in line 6 converts the decTotal variable to a string, and assigns the result to the lblTotal controls Text property. The form in the figure is from a project named Tab Order Demo, in the Chap3 folder of the student sample programs. You might produce a number such as 1.234567824724. For example, Forms, Buttons, and Labels have a Text property that works in the following manner: A Forms Text property determines the text that is displayed in the Forms title bar. 5.8 Assume lstNames is a list box and strSelectedName is a String variable. 5. Figure 2-81 A form with an Exit button btnExit In Tutorial 2-7 you will add an Exit button to the Guess the President application that you created in Tutorial 2-4. Figure 2-42 Code window and Designer tabs 1 Right-click Form1.vb in the Solution Explorer 2 Click View Code 2.3 Writing the Code for the Hello World Application If you detach the Code window and move it to another part of the screen, you can see the Code window and the Designer at the same time. Once the values are entered and the user clicks the Calculate Average button, check each input field for two criteria: 1. Single-stepping is the debugging technique of executing an applications programming statements one at a time. The following example uses -.2345: 23.45 % Specifying the Precision Each numeric format string can optionally be followed by an integer that indicates how many digits to display after the decimal point. In essence, intCount keeps track of the number of iterations the loop has performed. For each of the following controls, make up a legal name that conforms to the standard control name convention described in this chapter. Find the error and fix it. Summary Summary 10.1 Database Management Systems A database is a collection of one or more tables, each containing data related to a particular topic. It is also the mode that Visual Studio enters when a running application encounters a runtime error. 5.1 Input Boxes CONCEPT: Input boxes provide a simple way to gather input without placing a text box on a form. Once all syntax errors are corrected, run the program with test data for input. 2.13 Customizing an Applications Form Figure 2-94 Minimize, Maximize, and Close buttons on a form Maximize Minimize Close Tutorial 2-9: Setting the FormBorderStyle property and locking the controls on a form Step 1: Start Visual Studio and open the Guess the President project that you created in Tutorial 2-4. An algorithm is a set of well-defined steps for performing a task or solving a problem. T F: It is not possible to write Boolean expressions that contain math, relational, and logical operators. For example, two different templates loaded alternatively in OrderID column. The following control names appear in a Visual Basic application used in a retail store. (You may see a fourth type, Source Control, which we do not discuss in this book.) Step 4: Run the application and input the following test scores in the three text boxes: 80, 90, 75. Thats because you havent written the code for the buttons event handler. Upgrade to Internet Explorer 8 or newer for a better experience. 11. 11.17 Which list-type control automatically initializes its SelectedIndex property to zero? From there, you can find the "Data Source Configuration Wizard" (to reach it, click "Choose Data Source", "Add Project Data Source"). You store and work with values in an array by using a subscript. After a moment you should see a Reset Complete window. Private Sub btnExit_Click() Handles btnExit.Click ' Close the form. 6. For example, assume an application has a list box named lstEmployees. It is important to remember that the Name property and the Text property are two different things. 14. 11.3 Web Server Controls Figure 11-20 The Student Picnic application Step 1: Select New Web Site from the Visual Studio File menu. The user can select either Coffee, Tea, or Soft Drink by clicking the appropriate button. Enough space should be provided between field labels, columns, rows, and error messages. AllowAutoComplete property will autocomplete the input value by comparing it to each item of the underlying data source of GridMultiColumnDropDownList and returns the matched value by DisplayMember. . 4.4 The IfThenElseIf Statement The IfThenElseIf statement is like a chain of IfThenElse statements that perform their tests, one after the other, until one of them is found to be true. The following statement shows an example of how you would call the MessageBox.Show method to display the message box shown in Figure 2-88: MessageBox.Show("Thanks for clicking the button!") . It hosts CheckBox element as GridCell content. Converting TextBox Input VideoNote Converting TextBox Input The conversion functions listed in Table 3-11 are commonly used to convert values that the user has entered into TextBox controls. For example, when you are reading your own, or someone elses, code, and you see a variable name such as intUnitsSold, you immediately know that it is an Integer variable because of the int prefix. A table your program , each containing data related source connects data-bound controls to a dataset. The default value of PopUpMinHeight is 300.0. Programmers can write their applications in programming language statements, and then use special software called a compiler to convert the program into machine language. For instance, the following string has three leading spaces: " Hello" A trailing space is a space that appears at the end, or right side, of a string, after the nonspace characters. End If Dim str As String = "Hello" Dim intLength As Integer c. intLength = Length(str) If intZ < 10 Then lblResult.Text = "Invalid Data" d. Dim str As String = "123" If str.IsNumeric Then lblResult.Text = "It is a number." Also, we will modify the code behind the store clerk interface, so rentals may be saved in the database. Keywords (Reserved Words) Each high-level language has its own set of words that the programmer must learn in order to use the language. Use a parameterized query to retrieve the matching table rows and display them in a DataGridView control. The variable has class scope, so it is visible to both of the event handlers. 12. Figure 5-12 Output from the Do While Demo application Infinite Loops In all but rare cases, loops must contain within themselves a way to terminate. MessageBox.Show("un") End Sub Private Sub btnTwo_Click() Handles btnTwo.Click ' Display the French word for two. Preventing Data Conversion Exceptions In Chapter 3 you learned that an exception will occur if you try to convert the contents of a TextBox to a number, but the TextBox contains nonnumeric data. Complete the event handler by writing the code shown here in bold: Private Sub btnGo_Click() Handles btnGo.Click ' Variable declarations Dim intStartIndex As Integer ' Starting index of the search Dim intFoundIndex As Integer ' Index of the found substring ' Determine whether the starting index is numeric. Step 2: Set up the applications form as shown in Figure 2-74. a. b. c. d. Input Text Value Keyboard 219 220 Chapter 3 Variables and Calculations 2. They are shown for reference only, to help us discuss specific lines of code.) Figure 2-52 The Font dialog box Figure 2-53 A labels appearance with altered font attributes 2.4 More About Label Controls The BorderStyle Property Label controls have a BorderStyle property that allows you to display a border around the controls text. Unsigned integers can hold only positive values (zero is considered positive). lblDateToday.Text = Now.ToString("D") ' Get the current time from the system and display it. What is the purpose or Goal of Compatibility testing? If the expression is true, the statements in the body of the loop (lines 5 and 6) are executed. The names of the Click event handlers will be btnFirst_Click, btnSecond_Click, and btnThird_Click. Simply use an assignment statement to set the desired check boxs Checked property. Verify the parameter names, types and number of parameters. At runtime, when the user switches between the radio buttons, their event handlers can assign one of the two binding sources to the DataSource property of the DataGridView control. Step 3: Click inside the area that holds the Text propertys value and delete the current value. Number Roman Numeral 1 2 3 4 5 6 7 8 9 10 I II III IV V VI VII VIII IX X Input validation: Do not accept a number less than 1 or greater than 10. MessageBox.Show("quatre") End Sub Private Sub btnFive_Click() Handles btnFive.Click ' Display the French word for five. There are two formats: StringExpression.Substring(Start) StringExpression.Substring(Start, Length) The positions of the characters in StringExpression are numbered, with the first character at position 0. The names of the controls are shown in the figure. The function accepts a string as its argument and returns True if the string contains a number, or False if the strings contents cannot be recognized as a number. Dynamic Data: Controls that let you automatically generate Web pages from database tables. Table 4-8 Sales commission rates Sales This Month Commission Rate Less than $10,000 5% $10,000 $14,999 10% $15,000 $17,999 12% $18,000 $21,999 14% $22,000 or more 16% 273 274 Chapter 4 Making Decisions Because the staff is paid once per month, Crazy Als allows each employee to take up to $1,500 per month in advance pay. When there are multiple check boxes on a form or in a group box, any number of them can be selected at a given time. In the Properties window, give it a meaningful name such as 105 106 Chapter 2 Creating Applications with Visual Basic lblStatus. 10.5 Structured Query Language (SQL) SQL is a universal language for creating, updating, and retrieving data from databases. ", "Provide a Value") dblDistance = CDbl(strUserInput) Figure 5-2 Input box prompting for a distance You can also provide an optional third argument to the InputBox function, to specify a default input value. 8. You can customize the editor control while loading by overriding OnEditElementLoaded method. This is the second step performed on the computer. You can use the IntelliSense boxes to automatically complete some programming statements after typing only the first few characters. pulls data from one or more database tables and passes it to Multiple Choice 1. Line 5 declares a Decimal constant named decTWENTY_FIVE_CENTS_VALUE, initialized with the value 0.25D. After each statement executes, you can examine variable and property contents. First, in a DropDownList, the initial value of SelectedIndex is always 0, causing the first item to display when the form is loaded. can click the 85 86 Chapter 2 Creating Applications with Visual Basic Table 2-2 Form and control property settings Control Name Control Type Property Settings Form1 (Default name) Form Text: Guess the President Size: 280, 435 Label1 (Default name) Label Text: Who is this president? If the calories from fat are less than 30% of the total calories of the food, it should also display a message indicating the food is low in fat. People who look at screens all day usually like to see colors that do not tire their eyes. For example, suppose we know the number of minutes it will take to finish a job, and we want to calculate the number of hours that are contained in that many minutes.
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