Computer Programming Concepts and Visual Basic David I. Schneider

Private Sub ShowTitle()
‘Display source and title
Call Locate(-.5, -.1 * maxEnroll)
picEnroll.Print “Source: Statistical Abstract of the United States”
Call Locate(.5, 1.2 * maxEnroll)
picEnroll.Print “Two-Year College Enrollments (in thousands)”
End Sub
FIGURE 9-9 Chart for Example 1
Remarks on the program in Example 1
1. The value of tickFactor in the Sub procedure ShowLabels was set to 2 percent
of the scale determiners (numYears and maxEnroll) for the x and y axes. This
percentage is appropriate for picture boxes that occupy 1/4th to 1/3rd of the
screen. Smaller picture boxes might require a factor of 3 percent or 4 percent
for good-looking tick marks. Picture boxes that almost fill the screen might
have good results with a factor as small as 1 percent.
2. In the Sub procedure ShowLabels, the TextWidth and TextHeight methods were
used to obtain the width and height of each label. These values were used
together with the coordinates of the appropriate end of the tick mark to assign
values to CurrentX and CurrentY for proper placement of the label relative to
the graphics.
3. In the event procedure cmdDraw_Click, the number of data points (5) was
assigned to the variable numYears, and then numYears was used as a parameter
to all other Sub procedures. This feature makes it easy to add additional data to
the line chart. For instance, if we decide to include the data for one additional
year, we will only have to change the value of numYears and add one more line
to the data file.
■ LINE STYLING
Patterned, or “styled,” lines can be drawn between two points. Some available line styles are
shown in Figure 9-10. Each line has an associated number identifying its style. If s is one of
the numbers in the figure, then the statements
picBox.DrawStyle = s
picBox.Line (a, b)-(c, d)
draw the line from (a, b) to (c, d) in the style corresponding to the number s.
Line Charts 269