Computer Programming Concepts and Visual Basic David I. Schneider

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34 Computer Programming Concepts and Visual Basic button. After you click on Debug, the line containing the offending word will be highlighted. 7. At design time, colors are selected from a palette. At run time, the eight most common colors can be assigned with the color constants vbBlack, vbRed, vbGreen, vbYellow, vbBlue, vbMagenta, vbCyan, and vbWhite. For instance, the statement picBox.BackColor = vbYellow gives picBox a yellow background. 8. For statements of the form object.property = setting, with properties Caption, Text, or Font.Name, the setting must be surrounded by quotes. (For instance, lblTwo.Caption = “Name”, txtBox.Text = “Fore”, and picBox.Font.Name = “Courier”.) When the words True or False appear to the right of the equal sign, they should not be surrounded by quotation marks. 9. Code windows have many features of word processors. For instance, the operations cut, copy, paste, find, undo, and redo can be carried out with the sixth through eleventh icons of the Toolbar. These operations, and several others, also can be initiated from the Edit menu. 10. Names of existing event procedures associated with an object are not automatically changed when you rename the object. You must change them yourself and also must change any references to the object. Therefore, you should finalize the names of your objects before you put any code into their event procedures. 11. If you find the automatic List Properties/Methods feature distracting, you can turn it off by pressing Tools/Options, selecting the Editor page, and clicking on Auto List Members. If you do so, you can still display a list manually at the appropriate time by pressing Ctrl+J. 12. Earlier versions of Visual Basic used the property FontSize instead of Font.Size. Although Font.Size is preferred, FontSize is allowed for compatibility. Similarly, properties such as FontBold, FontItalic, and FontName have been included for compatibility with earlier versions of Visual Basic. 13. Assignment statements can be written preceded with the keyword Let. For instance, txtBox.Text = “Hello” also can be written Let txtBox.Text = “Hello”. Therefore, assignment statements are also known as Let statements. 2.3 NUMBERS Much of the data processed by computers consists of numbers. In “computerese,” numbers are often called numeric constants. This section discusses the operations that are performed with numbers and the ways numbers are displayed.
■ ARITHMETIC OPERATIONS The five arithmetic operations in Visual Basic are addition, subtraction, multiplication, division, and exponentiation. (Because exponentiation is not as familiar as the others, it is reviewed in detail in Comment 10.) Addition, subtraction, and division are denoted in Visual Basic by the standard symbols +, –, and /, respectively. However, the notations for multiplication and exponentiation differ from the customary mathematical notations. Mathematical Notation Visual Basic Notation a � b or a � b a * b ar a ^ r (The asterisk [*] is the upper character of the 8 key. The caret [^] is the upper character of the 6 key.) Note: In this book, the proportional font used for text differs from the monospaced font used for programs. In the program font, the asterisk appears as a five-pointed star (*). One way to show a number on the screen is to display it in a picture box. If n is a number, then the instruction picBox.Print n displays the number n in the picture box. If the picBox.Print instruction is followed by a combination of numbers and arithmetic operations, it carries out the operations and displays the result. Print is a reserved word and the Print operation is called a method. Another important method is Cls. The statement picBox.Cls erases all text and graphics from the picture box picBox. EXAMPLE 1 The following program applies each of the five arithmetic operations to the numbers 3 and 2. Notice that 3/2 is displayed in decimal form. Visual Basic never displays numbers as common fractions. Note 1: The star in the fifth and eighth lines is the computer font version of the asterisk. Note 2: The word “Run” in the phrasing [Run ...] indicates that F5 should be pressed to execute the program. Note 3: All programs appearing in examples and case studies are provided on the CD accompanying this book. See the discussion on the next to last page of the book for details. Below is the form design and a table showing the names of the objects on the form and the settings, if any, for properties of these objects. This form design is also used in the discussion and examples in the remainder of this section. Private Sub cmdCompute_Click() picResults.Cls picResults.Print 3 + 2 picResults.Print 3 - 2 picResults.Print 3 * 2 picResults.Print 3 / 2 picResults.Print 3 ^ 2 picResults.Print 2 * (3 + 4) End Sub [Run and then click the command button.] Object Property Setting frm3_3_1 Caption, 3-3-1 picResults cmdCompute Caption Compute Numbers 35
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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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