Computer Programming Concepts and Visual Basic David I. Schneider

362 Computer Programming Concepts and Visual Basic
SOLUTION:
We will create a new class, named CPFStudent, with the same member variables and property procedures
as the class CStudent. The only change needed in the class module occurs in the SemGrade method. The
new code for this method is
Public Function SemGrade() As String
Dim grade As Single
grade = (m_midterm + m_final) / 2
grade = Round(grade) ‘Round the grade
If grade = 60 Then
SemGrade = “Pass”
Else
SemGrade = “Fail”
End If
End Function
The only change needed in the Form code is to replace the two occurrences of CStudent
with CPFStudent. When the program is run with the same input as in Example 1, the output
will be
Adams, Al 123-45-6789 Pass
■ THE INITIALIZE EVENT PROCEDURE
The Object drop-down combo box in a class module window displays two items General and
Class. When you click on Class, the following template appears:
Private Sub Class_Initialize()
End Sub
This event procedure is automatically invoked when an object is created from the class. Any
code you type into the procedure is then executed. This procedure is used to set default values
for member variables and to create other objects associated with this object.
Since methods are created with ordinary Function or Sub procedures, arguments can be
passed to them when they are called. The graphical program in Example 3 makes use of arguments.
The program involves “twips,” which are a unit of screen measurement. (One inch is
about 1440 twips.) The settings for the Top, Left, Height, and Width properties of a control
are given in twips. For instance, the statements
Image1.Width = 1440 ‘1 inch
Image1.Height = 2160 ‘1.5 inch
Image1.Top = 2880 ‘2 inches
Image1.Left = 7200 ‘5 inches
set the size of the image control as 1” by 1.5”, and place the control 2 inches from the top of
the form and 5 inches from the left side of the form. (See Figure 6-6 in Section 6.3.) Programs
using the Height property of the form should have the BorderStyle property of the form set to
“0-None” since otherwise the height of the border is included in the height of the form.
EXAMPLE 3
Write a program containing a Circle object. The object should keep track of the center and radius of the
circle. (The center is specified by two numbers, called the coordinates, giving the distance from the left
side and top of the form. Distances and the radius should be measured in twips.) A Show method should
display the circle on the form and a Move method should add 500 twips to each coordinate of the center
of the circle. Initially, the circle should have its center at (500, 500) and radius 500. The form should have
a command button captioned “Move and Show Circle” that invokes both methods.