Lesson 14: Mastering Functions and Sub Procedures in VB6

Public Function FV(PV As Variant, i As Variant, n As Variant) As Variant
    ' Formula to calculate Future Value(FV)
    ' PV denotes Present Value 
    FV = PV * (1 + i / 100) ^ n
End Function

Private Sub compute_Click()
    ' This procedure will calculate Future Value 
    Dim FutureVal As Variant
    Dim PresentVal As Variant
    Dim interest As Variant
    Dim period As Variant
    PresentVal = PV.Text
    interest = rate.Text
    period = years.Text 
    ' Calling the function
    FutureVal = FV(PresentVal, interest, period)
    MsgBox ("The Future Value is " & FutureVal)
End Sub

Public Function grade(mark As Variant) As String 
    Select Case mark
        Case Is >= 80 
            grade = "A"
        Case Is >= 70
            grade = "B" 
        Case Is >= 60 
            grade = "C"
        Case Is >= 50 
            grade = "D"
        Case Is >= 40 
            grade = "E"
        Case Else 
            grade = "F"
    End Select
End Function

Private Sub compute_Click() 
    grading.Caption = grade(mark)
End Sub

Private Sub cmdCal_Click()
    Dim x As Single, y As Single
    x = Val(TxtNum1.Text)
    y = Val(TxtNum2.Text)
    ' Call the sub procedure
    sum x, y
End Sub

Sub sum(a As Single, b As Single)
    MsgBox ("sum = " & a + b)
End Sub

Public Sub buy_decision(size As Integer, price As Single)
    Dim buy As Boolean
    If size >= 7 And price <= 200 Then
        buy = True
        MsgBox ("Buy")
    Else
        buy = False
        MsgBox ("Don't Buy")
    End If
End Sub

Private Sub CmdDecide_Click()
    Dim shoe_size As Integer, shoe_price As Single
    shoe_size = TxtX.Text
    shoe_price = TxtY.Text
    ' Call the sub procedure
    buy_decision shoe_size, shoe_price
End Sub