Computer Programming Concepts and Visual Basic David I. Schneider

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266 Computer Programming Concepts and Visual Basic 2. The following technique can be used to determine a good range of values for a Scale method when graphs with only positive values are to be drawn. (a) Let r be the x coordinate of the rightmost point that will be drawn by any Line, PSet, or Circle method. (b) Let h be the y coordinate of the highest point that will be drawn by any Line, PSet, or Circle method. (c) Let the numbers on the x axis range from about –[20% of r] to about r + [20% of r]. Let the numbers on the y axis range from about –[20% of h] to about h + [20% of h]. That is, use picOutput.Scale (-.2 * r, 1.2 * h)-(1.2 * r, -.2 * h) 3. Usually one unit on the x axis is a different length than one unit on the y axis. The statement picBox.Circle (x, y), r draws a circle whose radius is r x-axis units. 4. If one or both of the points used in the Line method fall outside the picture box, the computer only draws the portion of the line that lies in the picture box. This behavior is referred to as line clipping and is used for the Circle method also. 5. A program can execute a picOutput.Scale statement more than once. Executing a new picOutput.Scale statement has no effect on the text and graphics already drawn; however, future graphics statements will use the new coordinate system. This technique can be used to produce the same graphics figure in different sizes and/or locations within the picture box. The output from the following event procedure is shown in Figure 9-8. Private Sub cmdDraw_Click() Dim i As Integer picOutput.Cls For i = 0 To 3 picOutput.Scale (0, 2 ^ i)-(2 ^ i, 0) picOutput.Line (0, 0)-(.5, 1) picOutput.Line (.5, 1)-(.8, 0) picOutput.Line (.8, 0)-(0, .8) picOutput.Line (0, .8)-(1, .5) picOutput.Line (1, .5)-(0, 0) Next i End Sub FIGURE 9-8 Output from Comment 5 6. The programs in this section can be modified to produce colorful displays. Lines, points, and circles can be drawn in color through use of the vbColor constants. To use color, place “, vbColor” at the end of the corresponding graphics statement. For instance, the statement picBox.Line (x1, y1)-(x2, y2), vbRed draws a red line.
9.2 LINE CHARTS A line chart displays the change in a certain quantity in relation to another quantity (often time). The following steps produce a line chart. 1. Look over the data to be displayed. A typical line chart displays between 3 and 20 items of data corresponding to evenly spaced units of time: years, months, or days. The positions on the x axis will contain labels such as “Jan Feb Mar Apr . . .” or “1996 1997 1998 1999 . . .”. These labels can be placed at the locations 1, 2, 3, . . . on the x axis. 2. Choose a coordinate system based on the number of data items and the size of the quantities. A convenient scale for the x axis is from –1 to one more than the number of data items. The scale for the y axis is determined by the largest quantity to be displayed. 3. Draw the line segments. It is a good idea to draw a small circle around the end points of the line segments. 4. Draw and label tick marks on the coordinate axes. The x axis should have a tick mark for each time period. The y axis should have at least one tick mark to indicate the magnitude of the quantities displayed. 5. Title the chart, and give the source of the data. EXAMPLE 1 Table 9.1 gives enrollment data for 2-year colleges taken from the Statistical Abstract of the United States (the data for 2000 is a projection). Write a program to display the total enrollments for the given years in a line chart. TABLE 9.1 Two-Year College Enrollments (in Thousands) Year 1960 1970 1980 1990 2000 Male 283 1375 2047 2233 2398 Female 170 945 2479 3007 3358 Total 453 2320 4526 5240 5756 SOLUTION: Figure 9-9 shows the graph that results from executing the following program. The data in ENROLL.TXT are taken from the first and fourth lines of Table 9.1. For example, the first line in the file is “1960”, 453. (Explanatory remarks follow the program.) ‘In (Declarations) section of (General) Dim numYears As Integer, maxEnroll As Single Private Sub cmdDraw_Click() ‘Line Chart of Total Two-Year College Enrollments numYears = 5 ReDim label(1 To numYears) As String ReDim total(1 To numYears) As Single Call ReadData(label(), total()) Call DrawAxes Call DrawData(total()) Call ShowTitle Call ShowLabels(label()) End Sub Private Sub DrawAxes() ‘Draw axes Line Charts 267
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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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Page 223: S E C T I O N 7 SEQUENTIAL FILES
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Page 251: S E C T I O N 8 RANDOM-ACCESS FILES
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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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