Computer Programming Concepts and Visual Basic David I. Schneider

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32 Computer Programming Concepts and Visual Basic FIGURE 2-20 The Three Event Procedures 10. Now run the program by pressing F5. 11. Type something into the text box. In Figure 2-21, the words “Hello Friend” have been typed. (A text box has the focus whenever it is ready to accept typing; that is, whenever it contains a blinking cursor.) FIGURE 2-21 Text Box Containing Input 12. Press the Tab key. The contents of the text box will be enlarged as in Figure 2- 22. When Tab was pressed, the text box lost the focus; that is, the event Lost- Focus happened to txtPhrase. Thus, the event procedure txtPhrase_ LostFocus was called, and the code inside the procedure was executed. FIGURE 2-22 Text Box After It Has Lost the Focus 13. Click on the command button. This calls the event procedure cmd Bold_Click, which converts the text to boldface. See Figure 2-23. FIGURE 2-23 Text Box After the Command Button Has Been Clicked
14. Click on the text box or press the Tab key to move the cursor (and, therefore, the focus) to the text box. This calls the event procedure txtPhrase_GotFocus, which restores the text to its original state. 15. You can repeat Steps 11 through 14 as many times as you like. When you are finished, end the program by pressing Alt+F4, clicking the End icon on the Toolbar, or clicking the Close button (X) on the form. COMMENTS 1. To hide the code window, press the right mouse button and click on Hide. You can also hide it by clicking on the icon at the left side of the title bar and clicking on Close. To view a hidden code window, press Alt/View/Code. To hide a form, close its container. To view a hidden form, press Alt/View/Object. 2. The form is the default object in Visual Basic code. That is, code such as Form1.property = setting can be written as property = setting Also, event procedures associated with Form1 appear as Form_event() rather than Form1_event() 3. Another useful command is SetFocus. The statement object.SetFocus moves the focus to the object. 4. We have ended our programs by clicking the End icon or pressing Alt+F4. A more elegant technique is to create a command button, call it cmdQuit, with caption Quit and the event procedure: Private Sub cmdQuit_Click() End End Sub 5. Certain words, such as Sub, End, and False, have special meanings in Visual Basic and are referred to as keywords or reserved words. The Visual Basic editor automatically capitalizes the first letter of a keyword and displays the word in blue. 6. Visual Basic can detect certain types of errors. For instance, consider the line txtPhrase.Font.Bold = False from the walkthrough. Suppose you neglected to type the word False to the right of the equal sign before leaving the line. Visual Basic would tell you something was missing by displaying the left message box at the top of page 66. (Also, the line would turn red.) On the other hand, suppose in the CmdBold_Click procedure you misspell the keyword “Bold” as “bolt.” You might notice something is wrong when the letter “b” is not capitalized. If not, you will certainly know about the problem when the program is run because Visual Basic will display the right message box at the top of page 66 when you click on the command Visual Basic Events 33
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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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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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