Lesson 14: Creating User-Defined Functions

14.1 Creating Your Own Function
The general format of a function is as follows:

Public  Function functionName (Arg As dataType,..........) As dataType
or
Private  Function functionName (Arg As dataType,..........) As dataType

* Public indicates that the function is applicable to the whole project and
   Private indicates that the function is only applicable to a certain module or procedure.

Example 14.1

In this example, a user can calculate the future value of a certain amount of money he has today based on the interest rate and the number of years from now,  supposing  he will invest this amount of money somewhere .The calculation is based on the compound interest rate. 

The code 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 funciton FutureVal = FV(PresentVal, interest, period) MsgBox ("The Future Value is " & FutureVal) End Sub Example 14.2 The following program will automatically compute examination grades based on the marks that a student obtained. The code is shown on the right. The Code 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 http://www.vbtutor.net/vb6/vbtutor.html