Visual Basic Functions

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Visual Basic Functions

• The least you need to know about functions.

Accompanying application illustration
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Functions

• A function is a type of subroutine which returns
  a value based on a passed parameter.
• ByVal functions do something useful with the
  passed parameter but do not change it.
• ByRef functions typically change the value of the
  passed parameter.

Same rules of scope as Procedures
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ByVal Parameter

• Private Sub btnSolution1_Click(ByVal sender As _
  System.Object, ByVal e As System.EventArgs) _
  Handles btnSolution1.Click
• DoubleIt(CDec(txtArgument1.Text))
• End Sub
• Private Function DoubleIt(ByVal decNumber1 As
  Decimal)
• txtFunction1.Text CStr(decNumber1 2)
• End Function

This function doubles the parameter passed to it
and displays it in a textbox. Any parameter
passed to this function will be known as
decNumber1 in this function.
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ByVal Parameter

• Private Sub btnSolution2_Click(ByVal sender As _
  System.Object, ByVal e As System.EventArgs)
  Handles _ btnSolution2.Click
• txtFunction2.Text _
  CStr(TripleIt(CDec(txtArgument2.Text)))
• End Sub
• Private Function TripleIt(ByVal decNumber2 As
  Decimal) As Decimal
• TripleIt decNumber2 3End Function

This function triples the parameter passed to it.
The identifier for the function is treated as a
variable and is the means by which the value is
returned.
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ByRef Parameter

• Private Sub btnSolution3_Click(ByVal sender
  As System.Object, _ ByVal e As System.EventArgs)
  Handles btnSolution3.Click
• Dim Argument3 As Decimal
• Argument3 CDec(txtArgument3.Text)
• TwiceIt(Argument3)
• txtFunction3.Text CStr(Argument3)
• End Sub
•  
• Private Function TwiceIt(ByRef decNumber As
  Decimal)
• decNumber decNumber 2
• End Function

The value of Argument3 becomes doubled by the
function.
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Why use Functions?

• Functions reduce the amount of code in a program.
• A function can be called again and again from any
  place in the program.

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Built-in Functions
and many more
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Built-in String Functions
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Randomize() function

• We need random numbers for games.
• Randomize(number) initializes the random-number
  generator.
• If you omit number, the value returned by the
  system timer is used as the new seed value.

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Rnd() returns a random positive number less than
1, but greater than or equal to zero.
Recipe for a random integer CInt(Int((upperbound
- lowerbound 1) Rnd() lowerbound))