Computer Programming Concepts and Visual Basic David I. Schneider

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260 Computer Programming Concepts and Visual Basic and (3) place text at appropriate points on the chart. The basic tools for accomplishing each of these steps follow. ■ SPECIFYING A COORDINATE SYSTEM Suppose we have a piece of paper, a pencil, and a ruler and we want to graph a line extending from (2, 40) to (5, 60). We would most likely use the following three-step procedure: 1. Use the ruler to draw an x axis and a y axis. Focus on the first quadrant because both points are in that quadrant. 2. Select scales for the two axes. For instance, we might decide that the numbers on the x axis range from –1 to 6 and that the numbers on the y axis range from –10 to 80. 3. Plot the two points and use the ruler to draw the straight-line segment joining them. EXAMPLE 1 (a) Draw a coordinate system with the numbers on the x axis ranging from –2 to 10, and the numbers on the y axis ranging from –3 to 18. (b) Draw the straight line from (1, 15) to (8, 6). (c) Draw the straight line from (–2, 0) to (10, 0). SOLUTION: (a) (b)
(c) The point (–2, 0) is the left-hand end point of the x axis and the point (10, 0) is the right-hand end point; therefore, the line joining them is just the portion of the x axis we have already drawn. We draw these graphs on the screen with the same three steps we use with paper, pencil, and ruler. The only difference is that we first do Step 2 and then Steps 1 and 3. The Visual Basic method Scale is used to specify the range of values for the axes and the method Line serves as the ruler. The statement picBox.Scale (a, d)-(b, c) specifies that numbers on the x axis range from a to b and that numbers on the y axis range from c to d. See Figure 9-2. The ordered pair (a, d) gives the coordinates of the top left corner of the picture box, and the ordered pair (b, c) gives the coordinates of the bottom right corner of the picture box. FIGURE 9-2 Result of Scale Method FIGURE 9-3 Result of the Line Method ■ GRAPHICS METHODS FOR DRAWING LINES, POINTS, AND CIRCLES After an appropriate coordinate system has been specified by a picBox.Scale statement, graphics can be drawn in the picture box using the Line and Circle methods. The statement picBox.Line (x1, y1)-(x2, y2) draws the line segment from the point with coordinates (x1, y1) to the point with coordinates (x2, y2) in the picture box (see Figure 9-3). In particular, the statement picBox.Line (a, 0)–(b, 0) draws the x axis and the statement picBox. Line (0, c)–(0, d) draws the y axis. The following event procedure produces the graph of Example 1, part (b): Private Sub cmdDraw_Click() picOutput.Cls picOutput.Scale (-2, 18)-(10, -3) ‘Specify coordinate system picOutput.Line (-2, 0)-(10, 0) ‘Draw x-axis picOutput.Line (0, -3)-(0, 18) ‘Draw y-axis picOutput.Line (1, 15)-(8, 6) ‘Draw the straight line End Sub Introduction to Graphics 261
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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
Page 251: S E C T I O N 8 RANDOM-ACCESS FILES
Page 265: S E C T I O N 9 THE GRAPHICAL DISPL
Page 295 and 296: 10.1 LIST BOXES AND COMBO BOXES The
Page 297 and 298: Private Sub cmdAdd_Click() Dim item
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Page 309 and 310: THE SHAPE CONTROL The shape control
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Page 313 and 314: Rows 9 ScrollBars 0 - flexScrollBar
Page 315 and 316: Private Sub cmdQuit_Click() End End
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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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