Computer Programming Concepts and Visual Basic David I. Schneider

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246 Computer Programming Concepts and Visual Basic Care must be taken when comparing an ordinary (variable-length) string with a fixedlength string or comparing two fixed-length strings of different lengths. EXAMPLE 2 In the following program, the strings assigned to the variables town, city, and municipality have lengths 7, 9, and 12, respectively, and therefore are all different. Private Sub cmdGo_Click() Dim town As String * 7 Dim city As String * 9 Dim municipality As String * 12 ‘Illustrate fixed-length strings town = “Chicago” city = “Chicago” municipality = “Chicago” picOutput.Cls If (city = town) Or (city = municipality) Then picOutput.Print “same” Else picOutput.Print “different” End If picOutput.Print “123456789012345” picOutput.Print city & ”***” picOutput.Print town & “***” picOutput.Print municipality & “***” End Sub [Set picOutput’s Font property to Courier. Run, and click the command button.] There are times when we want to consider the values assigned to variables of different types as being the same, such as city and town in Example 2. In this situation, the function RTrim comes to the rescue. If info is an ordinary string or a fixed-length string, then the value of RTrim(info) is the (variable-length) string consisting of info with all right-hand spaces removed. For instance, the value of RTrim(“hello”) is the string “hello”. In Example 2, if the If block is changed to If (RTrim(city) = town) And (RTrim(city) = RTrim(municipality)) Then picOutput.Print “same” Else picOutput.Print “different” End If then the first line of the output will be “same”.
■ RECORDS In this text, we have worked with numbers, strings, arrays, and now fixed-length strings. Strings and numbers are built-in data types that can be used without being declared, although we have always elected to declare numeric and string variables using Dim statements. On the other hand, arrays and fixed-length strings are user-defined data types that must be declared with a Dim statement before being used. A record is a user-defined data type that groups related variables of different types. Figure 8-1 shows an index card that can be used to hold data about colleges. The three pieces of data—name, state, and year founded—are called fields. Each field functions like a variable in which information can be stored and retrieved. The length of a field is the number of spaces allocated to it. In the case of the index card, we see that there are three fields having lengths 30, 2, and 4, respectively. The layout of the index card can be identified by a name, such as collegeData, called a record type. Name: State: Year Founded: FIGURE 8-1 An Index Card Having Three Fields For programming purposes, the layout of the record is declared by a block of statements similar to Type collegeData nom As String * 30 state As String * 2 yearFounded As Integer End Type User-Defined Data Types 247 Each character of a string is stored in a piece of memory known as a byte. Therefore, a field of type String * n requires n bytes of memory. However, numbers (that is, the integer or single-precision numbers we use in this text) are stored in a different manner than strings. Integer numbers always use two bytes of memory, whereas single-precision numbers always use four bytes of memory. Visual Basic requires that Type declarations, such as the preceding record structure collegeData, be placed in either (General) or in a special file, referred to as a BAS Module. When placed in the (General) portion of a form, the word “Type” must be preceded by “Private” and the record type is only valid for that form. When placed in a BAS module, the word “Type” may be preceded by either “Private” (valid for the current BAS module) or “Public” (valid throughout the entire program). In this text, we will primarily place our declarations inside BAS Modules and make them Public. To create a BAS Module for the program currently being designed, press Alt/P/M and double-click on Module. A window like the one in Figure 8-2 will appear. This window is where our Type declarations will be entered. To switch between this BAS Module window and the form(s), press Ctrl+R to activate the Project Explorer and double-click on a form or
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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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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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