6. Menu-Driven and Calculator Projects

Running the Project:

Select Start from the Run Menu.   Then by clicking the menu items draw the word hello for three different thickness.   The final run mode window will look as shown in the figure 4.

                           Figure 4

2. Calculator Project:

The basic layout of the screen is shown in the figure 5.   There are two control arrays of buttons one for the digits 0 to 9 and another for operators +, -, /, * and =.   The form is given the name ‘calculator’ and its icon property is set to calculator icon.   The display label is given the name ‘Readout’ and the caption ‘0.’. The number buttons 0 to 9  are given the same name ‘Number’, their captions and indexes are set as 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 respectively.    The operator buttons /, +, X, - and = are given the same name, “Operator” , and their indexes are set as 0, 1, 2, 3 and 4 respy.   The ‘%’  button is given the name ‘Percent’, the ‘.’  button is given the name ‘Decimal’, the ‘C’ button is given the name ‘Cancel’ and the ‘CE’ button is given the name ‘CancelEntry’.    The codes are entered in the code window  as shown in the figure 5a.   Save and run the project and  check that the calculator functions properly.  

                            Figure 5

Option Explicit

Dim Op1, Op2                ' Previously input operand.

Dim DecimalFlag As Integer  ' Decimal point present yet?

Dim NumOps As Integer       ' Number of operands.

Dim LastInput               ' Indicate type of last keypress event.

Dim OpFlag                  ' Indicate pending operation.

Dim TempReadout

' Click event procedure for C (cancel) key.

' Reset the display and initializes variables.

Private Sub Cancel_Click()

    Readout = Format(0, "0.")

    Op1 = 0

    Op2 = 0

    Form_Load

End Sub

' Click event procedure for CE (cancel entry) key.

Private Sub CancelEntry_Click()

    Readout = Format(0, "0.")

    DecimalFlag = False

    LastInput = "CE"

End Sub

' Click event procedure for decimal point (.) key.

' If last keypress was an operator, initialize

' readout to "0." Otherwise, append a decimal

' point to the display.

Private Sub Decimal_Click()

    If LastInput = "NEG" Then

        Readout = Format(0, "-0.")

    ElseIf LastInput <> "NUMS" Then

        Readout = Format(0, "0.")

    End If

    DecimalFlag = True

    LastInput = "NUMS"

End Sub

' Initialization routine for the form.

' Set all variables to initial values.

Private Sub Form_Load()

    DecimalFlag = False

    NumOps = 0

    LastInput = "NONE"

    OpFlag = " "

    Readout = Format(0, "0.")

    'Decimal.Caption = Format(0, ".")

End Sub

' Click event procedure for number keys (0-9).

' Append new number to the number in the display.

Private Sub Number_Click(Index As Integer)

    If LastInput <> "NUMS" Then

        Readout = Format(0, ".")

        DecimalFlag = False

    End If

    If DecimalFlag Then

        Readout = Readout + Number(Index).Caption

    Else

        Readout = Left(Readout, InStr(Readout, Format(0, ".")) - 1) + Number(Index).Caption + Format(0, ".")

    End If

    If LastInput = "NEG" Then Readout = "-" & Readout

    LastInput = "NUMS"

End Sub

' Click event procedure for operator keys (+, -, x, /, =).

' If the immediately preceeding keypress was part of a

' number, increments NumOps. If one operand is present,

' set Op1. If two are present, set Op1 equal to the

' result of the operation on Op1 and the current

' input string, and display the result.

Private Sub Operator_Click(Index As Integer)

    TempReadout = Readout

    If LastInput = "NUMS" Then

        NumOps = NumOps + 1

    End If

    Select Case NumOps

        Case 0

        If Operator(Index).Caption = "-" And LastInput <> "NEG" Then

            Readout = "-" & Readout

            LastInput = "NEG"

        End If

        Case 1

        Op1 = Readout

        If Operator(Index).Caption = "-" And LastInput <> "NUMS" And OpFlag <> "=" Then

            Readout = "-"

            LastInput = "NEG"

        End If

        Case 2

        Op2 = TempReadout

        Select Case OpFlag

            Case "+"

                Op1 = CDbl(Op1) + CDbl(Op2)

            Case "-"

                Op1 = CDbl(Op1) - CDbl(Op2)

            Case "X"

                Op1 = CDbl(Op1) * CDbl(Op2)

            Case "/"

                If Op2 = 0 Then

                   MsgBox "Can't divide by zero", 48, "Calculator"

                Else

                   Op1 = CDbl(Op1) / CDbl(Op2)

                End If

            Case "="

                Op1 = CDbl(Op2)

            Case "%"

                Op1 = CDbl(Op1) * CDbl(Op2)

            End Select

        Readout = Op1

        NumOps = 1

    End Select

    If LastInput <> "NEG" Then

        LastInput = "OPS"

        OpFlag = Operator(Index).Caption

    End If

End Sub

' Click event procedure for percent key (%).

' Compute and display a percentage of the first operand.

Private Sub Percent_Click()

    Readout = Readout / 100

    LastInput = "Ops"

    OpFlag = "%"

    NumOps = NumOps + 1

    DecimalFlag = True

End Sub

Figure 5a