Computer Programming Concepts and Visual Basic David I. Schneider

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170 Computer Programming Concepts and Visual Basic index = Asc(letter) charCount(index) = charCount(index) + 1 End If Next letterNum ‘List the tally for each letter of alphabet picLetterCount.Font = “Courier” picLetterCount.Cls column = 1 ‘Next column at which to display letter & count For letterNum = Asc(“A”) To Asc(“Z”) letter = Chr(letterNum) picLetterCount.Print Tab(column); letter; picLetterCount.Print Tab(column + 1); charCount(letterNum); column = column + 6 If column > 42 Then ‘only room for 7 sets of data in a line picLetterCount.Print column = 1 End If Next letterNum End Sub [Run, type in the given sentence, and click the command button.] COMMENTS 1. Arrays must be dimensioned in a Dim or ReDim statement before they are used. If a statement such as a(6) = 3 appears without a previous Dim or ReDim of the array a( ), then the error message “Sub or Function not defined” will be displayed when an attempt is made to run the program. 2. Subscripts in ReDim statements can be numeric expressions. Subscripts whose values are not whole numbers are rounded to the nearest whole number. Subscripts outside the range of the array produce an error message as shown below when the last line of the event procedure is reached.
3. The two arrays in Example 3 are referred to as parallel arrays because subscripted variables having the same subscript are related. 4. The integers m and n in the statement Dim arrayName(m To n) As varType can be positive, negative, or zero. The only restriction is that m cannot be greater than n. The same holds true for ReDim statements. 5. Until a value is assigned to an element of an array, the element has its default value. Numeric variables have a default value of 0, and string variables have the default value “”, the empty string. 6. The statement Dim arrayName(0 To n) As varType can be replaced by the statement Dim arrayName(n) As varType. The same holds for the ReDim statement. 7. An array whose range has been specified by a ReDim statement is said to be dynamic. If array1() is a dynamic array, and array2() is another array of the same data type (such as String), then the line array1 = array2 makes array1() an exact duplicate of array2(). It will have the same size and contain the same information. This feature was added in Visual Basic 6.0. 8. A dynamic array can be resized with another ReDim statement. However, the resized array loses all its information. If it is resized with the words ReDim Preserve, as much information as possible will be retained. 6.2 USING ARRAYS This section considers three aspects of the use of arrays: processing ordered arrays, reading part of an array, and passing arrays to procedures. ■ ORDERED ARRAYS An array is said to be ordered if its values are in either ascending or descending order. The following arrays illustrate the different types of ordered and unordered arrays. In an ascending ordered array, the value of each element is less than or equal to the value of the next element. That is, [each element] ≤ [next element]. For string arrays, the ANSI table is used to evaluate the “less than or equal to” condition. Using Arrays 171
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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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220 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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