Computer Programming Concepts and Visual Basic David I. Schneider

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292 Computer Programming Concepts and Visual Basic The same program with a style 0 combo box produces the output shown. DRIVE, DIRECTORY, AND FILE LIST BOX CONTROLS Boxes similar to those inside the Open Project dialog box of Figure 10-1 are available to any Visual Basic program via icons from the Toolbox. Visual Basic does much of the work of providing the appropriate lists for the three boxes. Windows determines the contents of the drive box. The programmer determines the contents of directory list boxes and file list boxes with Path properties. Most of the properties, methods, and events of list boxes are also valid for the three filerelated list boxes. For instance, in the file list box File1, File1.ListCount is the number of files and File1.List(n) is the name of the nth file, where counting begins with 0. The selected items for the three controls are identified by the Drive, Path, and FileName properties, respectively. For instance, in the drive list box Drive1, the selected drive is given by the string Drive1.Drive. Suppose a form contains a drive list box named Drive1, a directory list box named Dir1, and a file list box named File1. (These names are the default names supplied by Visual Basic.) When the user selects a new drive from the Drive1 list box, the directories in Dir1 should reflect this change. The proper event procedure to effect the change is Private Sub Drive1_Change() Dir1.Path = Drive1.Drive End Sub This event is triggered by clicking on the drive name or using the arrow keys to highlight the drive name and then pressing Enter. When the user selects a new directory in Dir1, the files in File1 can be changed with the event procedure Private Sub Dir1_Change() File1.Path = Dir1.Path End Sub This event procedure is triggered by double-clicking on a directory name. If the preceding two event procedures are in place, a change of the drive will trigger a change of the directory, which in turn will trigger a change in the list of files. The standard prefixes for the names of the drive, directory, and file list box controls are drv, dir, and fil, respectively. EXAMPLE 4 The following program can be used to display the full name of any file on any drive. Object Property Setting frmFiles drvList dirList filList Caption Select a File cmdDisplay picFileSpec Caption Display Complete Name of File
Private Sub cmdDisplay_Click() picFileSpec.Cls picFileSpec.Print dirList.Path; If Right(dirList.Path, 1) “\” Then picFileSpec.Print “\”; End If picFileSpec.Print filList.FileName End Sub Private Sub dirList_Change() filList.Path = dirList.Path End Sub Private Sub drvList_Change() dirList.Path = drvList.Drive End Sub [Run, select a drive, double-click on a directory, select a file, and then click the command button.] COMMENTS List Boxes and Combo Boxes 293 1. If a list or combo box is too short to display all the items that have been added to it, Visual Basic automatically places a vertical scroll bar on the right side of the list box. The user can then scroll to see the remaining items of the list. 2. When the Style property of a combo box is set to 2, the combo box becomes a dropdown list box. The Drive list box is an example of a dropdown list box. 3. Dropdown combo boxes (Style 0) are used in Windows applications as a text box with a “history list” (list of past entries) from which you can either type a new entry or select an old entry. 4. The standard Windows convention for opening a file is to double-click on a name in a file list box. The program must contain code for a DblClick event procedure to carry out this task. 5. File list boxes can be made to display selective lists based on wildcard characters by setting the Pattern property. For instance, setting File1.Pattern equal to “*.TXT” dictates that only files with the extension TXT will be displayed.
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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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Page 251: 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
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Page 309 and 310: THE SHAPE CONTROL The shape control
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Page 315 and 316: Private Sub cmdQuit_Click() End End
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Creating and Designing Databases 34
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9. When all fields have been specif
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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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