Computer Programming Concepts and Visual Basic David I. Schneider

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264 Computer Programming Concepts and Visual Basic text appropriately in the picture box is essential to good-looking graphs. A picture box has two properties, CurrentX and CurrentY, and two methods, TextHeight and TextWidth, that allow us to precisely position text alongside graphics. The properties CurrentX and CurrentY record the precise horizontal and vertical location at which the next character of text will be printed. By assigning appropriate values to these properties before executing a Print method, text can be positioned very precisely in the picture box. In the following event procedure, the coordinates of the right end of the tick mark are (x, y) = (.3, 3). As a first attempt at labeling a tick mark on the y axis, the CurrentX and CurrentY properties are set to these coordinates. The results are shown in Figure 9-7(a). Private Sub cmdDraw_Click() picOutput.Cls picOutput.Scale (-4, 4)-(4, -4) picOutput.Line (-4, 0)-(4, 0) ‘Draw x-axis picOutput.Line (0, -4)-(0, 4) ‘Draw y-axis picOutput.Line (-.3, 3)-(.3, 3) ‘Draw tick mark picOutput.CurrentX = .3 ‘Right end of tick mark picOutput.CurrentY = 3 ‘Same vertical position as tick mark picOutput.Print “y=3” End Sub ‘Label for tick mark FIGURE 9-7 Placing Labels: (a) First Attempt and (b) Second Attempt Note that the top of the text is even with the tick mark. This reflects the fact that the value of the CurrentY property used by Visual Basic is the location for the top of the character cursor. Ideally, the text should be moved up so that the tick mark aligns with the middle of the text. To do this, the value of the CurrentY property needs to be increased by one-half the height of the text. The following statement assigns a corrected value to the CurrentY property by using the TextHeight method to obtain the height of the text being used as the tick mark label. (Since c < d in the scale method, TextHeight returns (–1) � [height of text].) picOutput.CurrentY = 3 - picOutput.TextHeight(“y=3”) / 2 The result of using this corrected value for CurrentY is shown in Figure 9-7(b). When the TextHeight method is used, all characters have the same height. Thus the height of a string can be obtained by asking for the height of any single character. The following procedure uses the TextHeight method with a space character to center the text cursor at the requested graphic point. Private Sub PositionText(x As Single, y As Single) ‘Center text cursor at the point (x, y) picOutput.CurrentX = x picOutput.CurrentY = y – picOutput.TextHeight(“ ”) / 2 End Sub Another useful picture box method is TextWidth. Whereas the Len function returns the number of characters in a string, the TextWidth method considers the varying widths of characters and returns the physical width of the entire string in the units of the current scale for
the picture box. The TextWidth method is essential when centering text, as illustrated in the following example. EXAMPLE 5 Write an event procedure to display the phrase “Th-that’s all Folks!” centered and double underlined in a picture box with x values ranging from 0 to 6 and y values ranging from 0 to 4. SOLUTION: Centering text requires knowing the coordinates of the center of the picture box, which for the given ranges will be the point (3, 2). Next, we need the width and height of the text being centered. These values are available using the TextWidth and TextHeight methods. The text cursor needs to start with a CurrentX that is half the text’s width to the left of center and a CurrentY that is half the text’s height above center. The first underline can be placed at half the text’s height below center. The additional distance down to the second underline should be in proportion to the height of the text. We decided after some experimenting to use a proportion of 1/6th. Private Sub cmdDraw_Click() ‘Center and double underline a phrase Dim xCenter As Single, yCenter As Single, phrase as String Dim w As Single, h As Single, leftEdge As Single, rightEdge As Single Dim ul1Pos As Single, ul2Pos As Single picOutput.Scale (0, 4)-(6, 0) picOutput.Cls xCenter = 3 yCenter = 2 phrase = “Th-that’s all Folks!” w = picOutput.TextWidth(phrase) h = picOutput.TextHeight(“ ”) picOutput.CurrentX = xCenter - w / 2 picOutput.CurrentY = yCenter - h / 2 picOutput.Print phrase leftEdge = xCenter - w / 2 rightEdge = xCenter + w / 2 ul1Pos = yCenter + h / 2 ul2Pos = ul1Pos + h / 6 picOutput.Line (leftEdge, ul1Pos)-(rightEdge, ul1Pos) picOutput.Line (leftEdge, ul2Pos)-(rightEdge, ul2Pos) End Sub [Run, and then click the command button. The resulting picture box follows.] COMMENTS 1. In Examples 1 through 4, examples that produce graphs, the range of numbers on the axes extended from a negative number to a positive number. Actually, any value of a, b, c, and d can be used in a Scale method. In certain cases, however, you will not be able to display one or both of the axes on the screen. (For instance, after picOutput.Scale (1, 10)–(10, –1) has been executed, the y axis cannot be displayed.) Introduction to Graphics 265
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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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Page 295 and 296: 10.1 LIST BOXES AND COMBO BOXES The
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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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