Computer Programming Concepts and Visual Basic David I. Schneider

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180 Computer Programming Concepts and Visual Basic ready to reproduce as many copies as you desire. To create a copy, press Ctrl+V (or open the Edit menu and select Paste). The copy of txtBox(0) appears in the upper-left corner of the form. The value of the Index property for this new text box is 1; thus the text box is referred to as txtBox(1). Move this text box to the desired position. Press Ctrl+V again and another copy of txtBox(0) appears in the upper left corner of the form. Its Index property is 2. Move txtBox(2) to an appropriate position. Continue copying txtBox(0) in this manner until all desired controls have been created. It is important to note that all property settings of txtBox(0) are being passed (as default settings) to the other elements of the txtBox( ) control array, with the exception of the Index, Top, and Left settings. Thus, as a matter of efficiency, before you begin copying txtBox(0), set all properties that you want carried over to all elements of txtBox( ). For example, if you desire to have the Text property blank for all txtBox( ) elements, set the Text property of txtBox(0) to (blank) before starting the copying process. The preceding discussion gave a process for creating an array of text boxes. This same process applies to creating arrays of labels or any other control. In summary, the following steps create an array of controls while designing a form: 1. Add one instance of the desired control to the form. 2. Set the Index property of this control to 0. 3. Set any other properties of the control that will be common to all elements of the array. 4. Click on the control and then press Ctrl+C to prepare to make a copy of the control. 5. Press Ctrl+V to create a copy of the control. Position this control as desired. 6. Repeat Step 5 until all desired elements of the control array have been created. EXAMPLE 1 A department store has five departments. The following program requests the amount of sales for each department and displays the total sales. We use a control array of five labels and a control array of five text boxes to handle the input. For the label captions we use “Department 1”, “Department 2”, and so on. Because these labels are the same except for the number, we wait until run time and use a For...Next loop inside the Form_Load ( ) event procedure to assign the captions to each element of the lblDepart( ) control array. At design time, before making copies of lblDepart(0), we set the Alignment property to “1 – Right Justify” so that all elements of the array inherit this property. Similarly, the Text property of txtSales(0) is set to (blank) before copying. Object Property Setting frm7_3_1 Caption (blank) lblDepart() Index 0 to 4 Alignment 1 – Right Justify txtSales( ) Index 0 to 4 Text (blank) cmdCompute Caption Compute Total Sales picTotal Private Sub Form_Load() Dim depNum As Integer For depNum = 0 To 4 lblDepart(depNum).Caption = “Department” & Str(depNum + 1) Next depNum End Sub Private Sub cmdCompute_Click() Dim depNum As Integer, sales As Single
sales = 0 For depNum = 0 To 4 sales = sales + Val(txtSales(depNum).Text) Next depNum picTotal.Cls picTotal.Print “Total sales were ”; FormatCurrency(sales) End Sub [Run, type the following data into the text boxes, and click the command button.] ■ CONTROL ARRAY EVENT PROCEDURES In Section 3 we discussed several events related to text boxes. One example was the GotFocus event procedure. If txtBox is an ordinary text box, then the GotFocus event procedure begins with the statement Private Sub txtBox_GotFocus() If, on the other hand, we make txtBox a control array, the GotFocus event procedure begins with the statement Private Sub txtBox_GotFocus(Index As Integer) Two points should be noted. First, even though we may have a dozen or more elements in the txtBox( ) control array, we will have just one txtBox_GotFocus event procedure to deal with. Second, Visual Basic passes to this one event procedure the value of the Index property for the element of the control array that has just received the focus. We may wish to respond in the same manner whenever any element of txtBox( ) has the focus, in which case we simply ignore the value of Index. If, on the other hand, we wish to respond in different ways, depending on which element has the focus, then we write the GotFocus event procedure in the form Private Sub txtBox_GotFocus(Index As Integer) Select Case Index Case 0 action when txtBox( ) gets the focus Case 1 action when txtBox(1) gets the focus . . End Select End Sub In general, all event procedures for a control array have the additional parameter Index As Integer. This additional parameter can be used, if desired, to base the action taken by the event procedure on which element of the control array underwent the event. EXAMPLE 2 The following program creates an electronic dialing pad. The form contains a control array of 10 command buttons. Each time a command button is clicked, the Index parameter conveys the digit to be added onto the phone number. This program illustrates using the Index parameter without employing a Select Case statement. Control Arrays 181
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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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230 Computer Programming Concepts a
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S E C T I O N 8 RANDOM-ACCESS FILES
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S E C T I O N 9 THE GRAPHICAL DISPL
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10.1 LIST BOXES AND COMBO BOXES The
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Private Sub cmdAdd_Click() Dim item
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either typing in information or jus
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Private Sub cmdDisplay_Click() picF
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clicks on the square to toggle betw
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circle and the button is said to be
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hsbBar.Value changes accordingly. T
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THE SHAPE CONTROL The shape control
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FIGURE 10-9 A Picture Created with
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Rows 9 ScrollBars 0 - flexScrollBar
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Private Sub cmdQuit_Click() End End
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Here, the menu bar contains two men
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Clipboard.Clear deletes the content
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cedures that are available to all f
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The Flags property influences certa
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13. Additional forms serve as new w
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6. Voting Machine. The members of t
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11.1 AN INTRODUCTION TO DATABASES T
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9. Click on the down arrow to the r
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clicked or a Move, Update, Delete,
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Do While (Not foundFlag) And (Not d
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mary key. Databases of student enro
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question mark stands for a single c
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1995 populations. When the second c
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If a Find method does not locate a
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place an x in the check box next to
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population (in descending order). W
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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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