Computer Programming Concepts and Visual Basic David I. Schneider

296 Computer Programming Concepts and Visual Basic
When a check box has the focus, the spacebar can be used to check (or uncheck) the box
and invoke the Click event. In addition, the state of a check box can be toggled from the keyboard
without first setting the focus to the check box if you create an access key for the check
box by including an ampersand in the Caption property. (Access keys appear underlined at
run time.) For instance, if the Caption property for the Dental Plan in Example 1 is set as
“&Dental Plan”, then the user can check (or uncheck) the box by pressing Alt+D.
Notice that the program code for the solution to Example 1 involved four identical click
event procedures. This is a good indication that a control array of check boxes will simplify
the program, as shown in Example 2.
EXAMPLE 2
The following program reworks Example 1 using a control array of check boxes, with an access key for
each check box. The program has been made more general and easy to update by placing the name and
cost of each benefit plan in the data file BENEFITS.TXT. Each line of the file consists of the name of the
plan followed by the cost of the plan, as illustrated by the first line of the file:
“&Prescription Drug Plan”, 12.51
Object Property Setting
frmBenefits Caption Benefits Menu
chkPlan( ) Index 0 through 3
lblTotal Caption Total monthly payment:
lblAmount Caption $0.00
Dim price(0 To 3) As Single ‘In (Declarations) section of (General)
Dim sum As Single
Private Sub Form_Load()
Dim i As Integer, plan As String, cost As Single
Open “BENEFITS.TXT” For Input As #1
For i = 0 To 3
Input #1, plan, cost
price(i) = cost
chkPlan(i).Caption = plan & “ (” & FormatCurrency(cost) & “)”
Next i
Close 1
sum = 0
End Sub
Private Sub chkPlan_Click(Index As Integer)
If chkPlan(Index).Value = 1 Then
sum = sum + price(Index)
Else
sum = sum - price(Index)
End If
lblAmount.Caption = FormatCurrency(sum)
End Sub
The Value property of a check box also can be set to “2-Grayed”. When a grayed square
is clicked, it becomes unchecked. When clicked again, it becomes checked.
THE OPTION BUTTON CONTROL
Option buttons are used to give the user a single choice from several options. Normally, a
group of several option buttons is attached to a frame or picture box with the single-clickdraw
technique. Each button consists of a small circle accompanied by text that is set with the
Caption property. When a circle or its accompanying text is clicked, a solid dot appears in the