Computer Programming Concepts and Visual Basic David I. Schneider

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296 Computer Programming Concepts and Visual Basic When a check box has the focus, the spacebar can be used to check (or uncheck) the box and invoke the Click event. In addition, the state of a check box can be toggled from the keyboard without first setting the focus to the check box if you create an access key for the check box by including an ampersand in the Caption property. (Access keys appear underlined at run time.) For instance, if the Caption property for the Dental Plan in Example 1 is set as “&Dental Plan”, then the user can check (or uncheck) the box by pressing Alt+D. Notice that the program code for the solution to Example 1 involved four identical click event procedures. This is a good indication that a control array of check boxes will simplify the program, as shown in Example 2. EXAMPLE 2 The following program reworks Example 1 using a control array of check boxes, with an access key for each check box. The program has been made more general and easy to update by placing the name and cost of each benefit plan in the data file BENEFITS.TXT. Each line of the file consists of the name of the plan followed by the cost of the plan, as illustrated by the first line of the file: “&Prescription Drug Plan”, 12.51 Object Property Setting frmBenefits Caption Benefits Menu chkPlan( ) Index 0 through 3 lblTotal Caption Total monthly payment: lblAmount Caption $0.00 Dim price(0 To 3) As Single ‘In (Declarations) section of (General) Dim sum As Single Private Sub Form_Load() Dim i As Integer, plan As String, cost As Single Open “BENEFITS.TXT” For Input As #1 For i = 0 To 3 Input #1, plan, cost price(i) = cost chkPlan(i).Caption = plan & “ (” & FormatCurrency(cost) & “)” Next i Close 1 sum = 0 End Sub Private Sub chkPlan_Click(Index As Integer) If chkPlan(Index).Value = 1 Then sum = sum + price(Index) Else sum = sum - price(Index) End If lblAmount.Caption = FormatCurrency(sum) End Sub The Value property of a check box also can be set to “2-Grayed”. When a grayed square is clicked, it becomes unchecked. When clicked again, it becomes checked. THE OPTION BUTTON CONTROL Option buttons are used to give the user a single choice from several options. Normally, a group of several option buttons is attached to a frame or picture box with the single-clickdraw technique. Each button consists of a small circle accompanied by text that is set with the Caption property. When a circle or its accompanying text is clicked, a solid dot appears in the
circle and the button is said to be “on.” At most one option button in a group can be on at the same time. Therefore, if one button is on and another button in the group is clicked, the first button will turn off. By convention, the names of option buttons have the prefix opt. The Value property of an option button tells if the button is on or off. The property optButton.Value is True when optButton is on and False when optButton is off. The statement optButton.Value = True turns on optButton and turns off all other buttons in its group. The statement optButton.Value = False turns off optButton and has no effect on the other buttons in its group. The Click event for an option button is triggered only when an off button is turned on. It is not triggered when an on button is clicked. EXAMPLE 3 The following program tells you if an option button is on. Private Sub cmdStatus_Click() picStatus.Cls If optOpt1.Value Then picStatus.Print “Option1 is on.” ElseIf optOpt2.Value Then picStatus.Print “Option2 is on.” End If End Sub Object Property Setting frmOptions Caption Option Buttons fraOptions Caption Options optOpt1 optOpt2 cmdStatus Caption Determine Status picStatus Private Sub Form_Load() optOpt1.Value = False ‘Turn off optOpt1 optOpt2.Value = False ‘Turn off optOpt2 End Sub [Run, click on one of the option buttons, and then click the command button.] Nine Elementary Controls 297 The text alongside an option button is specified with the Caption property. As with a command button and a check box, an ampersand can be used to create an access key for an option button.
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Computer Programming Concepts and V
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CONTENTS SECTION 1: PROBLEM SOLVING
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13.3 WEB PAGE PROGRAMMING WITH VBSC
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S E C T I O N 1 PROBLEM SOLVING
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4 Computer Programming Concepts and
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10 Computer Programming Concepts an
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S E C T I O N 2 FUNDAMENTALS OF PRO
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3.1 SUB PROCEDURES, PART I Structur
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The second task performed by the ad
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‘The density (number of people pe
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"Hawaii", 1184000, 6471 "Alaska", 6
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dure by just using the variable in
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Call CalculateSum(x, y, s) Call Dis
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■ FORM-LEVEL VARIABLES Visual Bas
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3. In Appendix D, the section “St
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Private Sub cmdDetermine_Click() Di
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Private Sub cmdCompute_Click() Dim
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preceded with the word ByVal. Built
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It is clear from the hierarchy char
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The meaningful procedure names, alo
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FIGURE 3-9 Sample Run for Programmi
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4.1 RELATIONAL AND LOGICAL OPERATOR
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(a) (2 < n) And (n < 6) (b) (2 < n)
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SOLUTION: In the following program,
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The Else part of an If block can be
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picTax.Cls picTax.Print “Your FIC
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Case 4, 5 picOutcome.Print “You a
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EXAMPLE 3 The following program use
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Case Else picResult.Print “The st
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4. The items in the value list must
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The hierarchy chart in Figure 4-4 s
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‘Program to compute employees’
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Private Function TaxMarried(adjPay
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and tells us whether the food meets
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S E C T I O N 5 REPETITION
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132 Computer Programming Concepts a
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S E C T I O N 6 ARRAYS
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S E C T I O N 7 SEQUENTIAL FILES
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S E C T I O N 8 RANDOM-ACCESS FILES
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Page 265: S E C T I O N 9 THE GRAPHICAL DISPL
Page 295 and 296: 10.1 LIST BOXES AND COMBO BOXES The
Page 297 and 298: Private Sub cmdAdd_Click() Dim item
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Page 309 and 310: THE SHAPE CONTROL The shape control
Page 311 and 312: FIGURE 10-9 A Picture Created with
Page 313 and 314: Rows 9 ScrollBars 0 - flexScrollBar
Page 315 and 316: Private Sub cmdQuit_Click() End End
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Creating and Designing Databases 34
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TABLE 11.5(B) TABLE 11.5(C) course
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(a) Update the quantity field of th
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12.1 CLASSES AND OBJECTS noun A wor
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Task Statement Assign a value to a
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EXAMPLE 1 and then an instance of t
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[Run, enter the data for a student
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SOLUTION: Object Property Setting f
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4. Methods can be either Function o
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‘Student Class (CStudent) Private
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txtFinal.Text = “” picGrades.Pr
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■ EVENTS In the previous section
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frmCircles.ForeColor = vbRed ‘Mak
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Public Function X() As Integer X =
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End Sub Private Sub cmdDropBomb_Cli
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Next i End Sub Public Function Read
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Remove method. The number of object
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S E C T I O N 13 COMMUNICATING WITH
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A P P E N D I C E S
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APPENDIX C VISUAL BASIC STATEMENTS,
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CANCEL The Cancel property provides
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COLS and ROWS The Cols and Rows pro
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DEFINT, DEFLNG, DEFSNG, DEFDBL, DEF
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ENVIRON Visual Basic has an environ
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FONT.ITALIC or FONTITALIC These pro
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yields “1234.”, Format(1234000,
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the length of the string currently
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ISNUMERIC The value of the function
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Unlock statement is used to remove
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Focus Default Default Number First
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OR (Logical Operator) The logical e
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the same as in the original Dimensi
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SECOND The function Second extracts
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STRETCH When the Stretch property o
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UNLOCK The Unlock command is intend
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[COLOR]: Numbers written in base 16
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Appendix D 457
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466 Technology of the Internet D Da
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468 Technology of the Internet Rela
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470 Technology of the Internet 2. D
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SYSTEM REQUIREMENTS CD-ROM INSTRUCT
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Computer Programming Concepts and Visual Basic David I. Schneider

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