Today’s Menu:

Functions…

To outline what you are going to do. Instead of doing it there, you write it somewhere else and give it a call.

There are two types of functions.

·         Built in functions – most mathematical functions are built in funtions.

·         User defined functions

Referenced from: http://72.14.207.104/search?q=cache:oxLTmINI14QJ:www.math.uaa.alaska.edu/~afkjm/cs109/handouts/Chap1.pdf+vb+function+calculate+gross+pay&hl=en&gl=us&ct=clnk&cd=6
Computing Gross Pay

Display message: "How many hours did you work?"

Allow user to enter number of hours worked

Store the number the user enters in memory

Display message: "How much are you paid per hour?"

Allow the user to enter an hourly pay rate

Store the number the user enters in memory

Multiply hours worked by pay rate and store the result in

Memory.

Display a message with the result of the previous step

This well-defined, ordered set of steps for solving a problem

is called an algorithm

referenced from: http://www.vbtutor.net/lesson11.html

11.1 Creating Your Own Functions
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 program and
   Private indicates that the function is only applicable to a certain module or procedure.
 
Example 11.1

In this example, a user can calculate 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.

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

FutureVal = FV(PresentVal, interest, period)
MsgBox ("The Future Value is " & FutureVal)
End Sub

Our version with some minor changes without functions.
   Dim FutureVal As Double

        Dim PresentVal As Double

        Dim interest As Integer

        Dim period As Integer

        PresentVal = PV.Text

        interest = Rate.Text

        period = years.Text

        FutureVal = FormatCurrency(PresentVal * (1 + interest / 100) ^ period)

        MsgBox("The Future Value is " & FutureVal)

Now, same program using functions…

Function computefuturevalue(ByVal PresentVal, ByVal interest, ByVal period)

        computefuturevalue = FormatCurrency(PresentVal * (1 + interest / 100) ^ period)

    End Function

    Private Sub compute_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles compute.Click

        Dim FutureVal As Double

        Dim PresentVal As Double

        Dim interest As Integer

        Dim period As Integer

        PresentVal = PV.Text

        interest = rate.Text

        period = years.Text

        FutureVal = computefuturevalue(PresentVal, interest, period)

        MsgBox("The Future Value is " & FutureVal)

Convert Case Study 5 to Case Study 6: Work with a function

Use a function and make it to work…