Computer Programming Concepts and Visual Basic David I. Schneider

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point. (Pressing F9 is referred to as toggling a breakpoint. You also can toggle a breakpoint with the Toggle Breakpoint option from the Debug menu.) 10. Press F5 and click on the command button. Respond to the request by entering 5. The program executes the first three lines and stops at the breakpoint. The breakpoint line is not executed. 11. Open the Immediate window by pressing Ctrl+G. If necessary, clear the contents of the window. Type the statement Print “num =”; num into the Immediate window and then press Enter to execute the statement. The appearance of “num = 6” on the next line of the Immediate window confirms that the breakpoint line was not executed. 12. Press F7 to return to the Code window. 13. Move the cursor to the line num = num + 1 and then press Ctrl+F9 to specify that line as the next line to be executed. (You can also use the Set Next Statement option from the Debug menu.) 14. Press F8 to execute the selected line. 15. Press Ctrl+G to return to the Immediate window. Move the cursor to the line containing the Print method and press Enter to confirm that the value of num is now 7, and then return to the Code window. 16. Move the cursor to the breakpoint line and press F9 to deselect the line as a breakpoint. 17. Press F5 to execute the remaining lines of the program. Observe that the value displayed in the picture box is 9. General Comment: As you step through a program, the form will become hidden from view. However, the form will be represented by a button on the Windows taskbar at the bottom of the screen. The button will contain the name of the form. You can see the form at any time by clicking on its button. STEPPING THROUGH A PROGRAM CONTAINING A GENERAL PROCEDURE: SECTION 3 The following walkthrough uses the single-stepping feature of the debugger to trace the flow through a program and a Sub procedure 1. Create a form with a command button (cmdButton) and a picture box (picBox). Set the AutoRedraw property of the picture box to True. Then enter the following two Sub procedures: Private Sub cmdButton_Click() Dim p As Single, b As Single picBox.Cls p = 1000 ‘Principal Call GetBalance(p, b) picBox.Print “The balance is”; b End Sub Private Sub GetBalance(prin As Single, bal As Single) ‘Calculate the balance at 5% interest rate Dim interest As Single interest = .05 * prin bal = prin + interest End Sub 2. Press F8, click the command button, and press F8 again. The picBox.Cls statement is highlighted to indicate that it is the next statement to be executed. Appendix D 461
462 Computer Programming Concepts and Visual Basic 3. Press F8 two more times. The Call statement is highlighted. 4. Press F8 once and observe that the heading of the Sub procedure GetBalance is now highlighted in yellow. 5. Press F8 three times to execute the assignment statements and to highlight the End Sub statement. (Notice that the Dim and Rem statements were skipped.) 6. Press F8 and notice that the yellow highlight has moved back to the cmdButton_Click event procedure and is on the statement immediately following the Call statement. 7. Click on the End icon to end the program. 8. Repeat Steps 2 and 3, and then press Shift+F8 to step over the procedure Get- Balance. The procedure has been executed in its entirety. 9. Click on the End icon to end the program. COMMUNICATION BETWEEN ARGUMENTS AND PARAMETERS The following walkthrough uses the Locals window to monitor the values of arguments and parameters during the execution of a program. 1. If you have not already done so, type the preceding program into the Code window. 2. Press F8 and click on the command button. 3. Select “Locals Window” from the View window. Notice that the variables from the cmdButton_Click event procedure appear in the Locals window. 4. Press F8 three more times to highlight the Call statement. Notice that the value of the variable p has changed. 5. Press F8 to call the Sub procedure. Notice that the variables displayed in the Locals window are now those of the procedure GetBalance. 6. Press F8 three times to execute the procedure. 7. Press F8 to return to cmdButton_Click event procedure. Notice that the value of the variable b has inherited the value of the variable bal. 8. Click on the End icon to end the program. STEPPING THROUGH PROGRAMS CONTAINING SELECTION STRUCTURES: SECTION 4 If Blocks The following walkthrough demonstrates how an If statement evaluates a condition to determine whether to take an action. 1. Create a form with a command button (cmdButton) and a picture box (picBox). Set the AutoRedraw property of the picture box to True. Then open the Code window and enter the following procedure: Private Sub cmdButton_Click() Dim wage As Single picBox.Cls wage = Val(InputBox(“wage:”)) If wage < 5.15 Then picBox.Print “Below minimum wage.” Else picBox.Print “Wage Ok.” End If End Sub
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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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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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Page 431 and 432: APPENDIX C VISUAL BASIC STATEMENTS,
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Page 481: SYSTEM REQUIREMENTS CD-ROM INSTRUCT
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Computer Programming Concepts and Visual Basic David I. Schneider

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