Computer Programming Concepts and Visual Basic David I. Schneider

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196 Computer Programming Concepts and Visual Basic 2. In Example 3, parallel arrays already ordered by one field were sorted by another field. Usually, parallel arrays are sorted by the field to be searched when accessing the file. This field is called the key field. 3. Suppose an array of 2000 items is searched sequentially—that is, one item after another—in order to locate a specific item. The number of comparisons would vary from 1 to 2000, with an average of 1000. With a binary search, the number of comparisons would be at most 11 because 211 > 2000. 4. The built-in function UCase converts all the characters in a string to uppercase. UCase is useful in sorting and searching arrays of strings when the alphabetic case (upper or lower) is unimportant. For instance, Example 5 includes UCase in the Select Case comparisons, and so the binary search will locate “Mobil” in the array even if the user entered “MOBIL”. 5. The Visual Basic function Timer can be used to determine the speed of a sort. Precede the sort with the statement t = Timer. After the sort has executed, the statement picOutput.Print Timer – t will display the duration of the sort in seconds. 6.5 TWO-DIMENSIONAL ARRAYS Each array discussed so far held a single list of items. Such array variables are called singlesubscripted variables. An array can also hold the contents of a table with several rows and columns. Such arrays are called two-dimensional arrays or double-subscripted variables. Two tables follow. Table 6.4 gives the road mileage between certain cities. It has four rows and four columns. Table 6.5 shows the leading universities in three disciplines. It has three rows and five columns. TABLE 6.4 Road Mileage Between Selected U.S. Cities Chicago Los Angeles New York Philadelphia Chicago 0 2054 802 738 Los Angeles 2054 0 2786 2706 New York 802 2786 0 100 Philadelphia 738 2706 100 0 TABLE 6.5 University Rankings 1 2 3 4 5 Business U of PA U of IN U of MI UC Berk U of VA Comp Sci. MIT Cng-Mellon UC Berk Cornell U of IL Engr/Gen. U of IL U of OK U of MD Cng-Mellon CO Sch. of Mines Source: A Rating of Undergraduate Programs in American and International Universities, Dr. Jack Gourman, 1998 Two-dimensional array variables store the contents of tables. They have the same types of names as other array variables. The only difference is that they have two subscripts, each with its own range. The range of the first subscript is determined by the number of rows in the table, and the range of the second subscript is determined by the number of columns. The statement
dimensions an array of type varType corresponding to a table with rows labeled from m1 To n1 and columns labeled from m2 To n2. The entry in the jth row, kth column is arrayName (j,k). For instance, the data in Table 6.4 can be stored in an array named rm( ). The statement Dim rm(1 To 4, 1 To 4) As Single will dimension the array. Each element of the array has the form rm(row, column). The entries of the array are rm(1,1)=0 rm(1,2)=2054 rm(1,3)=802 rm(1,4)=738 rm(2,1)=2054 rm(2,2)=0 rm(2,3)=2786 rm(2,4)=2706 rm(3,1)=802 rm(3,2)=2786 rm(3,3)=0 rm(3,4)=100 rm(4,1)=738 rm(4,2)=2706 rm(4,3)=100 rm(4,4)=0 As with one-dimensional arrays, when a two-dimensional array is created using Dim in the (Declarations) section of (General), the array becomes a form-level subscripted variable, and is therefore accessible in all event procedures and general procedures and retains whatever values are assigned until the program is terminated. Two-dimensional arrays also can be created with Dim that are local to a procedure and cease to exist once the procedure is exited. When the range of the subscripts is given by one or more variables, the proper statement to use is ReDim arrayName(m1 To n1, m2 To n2) As varType The data in Table 7.10 can be stored in a two-dimensional string array named univ( ). The statement Dim univ(1 To 3, 1 To 5) As String will dimension the array as form-level. Some of the entries of the array are univ(1,1) = “U of PA” univ(2,3) = “UC Berk” univ(3,5) = “CO Sch. of Mines” EXAMPLE 1 Write a program to store and access the data from Table 6.4. SOLUTION: Data are read from the data file DISTANCE.TXT into a two-dimensional form-level array using a pair of nested loops. The outer loop controls the rows and the inner loop controls the columns. Object Property Setting frmDist Caption Intercity Distances lblCh Caption 1. Chicago lblLA Caption 2. Los Angeles lblNY Caption 3. New York lblPh Caption 4. Philadelphia lblOrig Caption Origin txtOrig Text (blank) lblDest Caption Destination txtDest Text (blank) cmdShow Caption Show Mileage between Origin and Destination picMiles Dim rm(1 To 4, 1 To 4) As Single ‘In (Declarations) section of (General) Private Sub cmdShow_Click() Dim row As Integer, col As Integer ‘Determine road mileage between cities row = Val(txtOrig.Text) col = Val(txtDest.Text) Two-Dimensional Arrays 197
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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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Page 167: S E C T I O N 6 ARRAYS
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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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