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Event Driven Programming

A variable passed to a function procedure is normally passed by value. It can
also be passed by reference and thereby possibly have its value changed by
the function procedure. However, passing a variable by reference violates
good design principles, since a function is intended to only create a single
result and not cause any other changes.

Two examples of function procedure are as follows:
function FtoC(ByVal t As Double) As Double
‘Convert Fahrenheit temperature to Celsius
Return (5/9) * (t –32)
End function
function FirstName(ByVal name As String) As String
‘Extract the first name from a full name
Dim firstSpace As Integer
firstSpace = name.IndexOf(“ “)
Return name.Substring(0, firstSpace)
End function
The value of each of the preceding function is assigned by a statement of the form return
expression. The variables t and name appearing in the preceding function are parameters. They
can be replaced with any variable of the same type without affecting the function definition. For
instance, the function FtoC could have been defined as
function FtoC(ByVal temp As Double) As Double
‘Convert Fahrenheit temperature to Celsius
Return (5/9) * (temp –32)
End function

1: The following program uses the function FtoC.

Object Property Setting

frmConvert Text Convert Fahrenheit to Celsius
lblTempF Text Temperature (Fahrenheit)
txtTempF

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