Sub Procedures; Passing Values Back From Sub Procedures

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Sub ProceduresPassing Values Back From Sub
Procedures

• Passing by reference
• Passing by value

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Passing Arguments By Reference

• Passing arguments by reference gives the
  procedure access to the actual variable contents
  in its memory address location.
• The variable's value can be permanently changed
  by the procedure to which it is passed.
• Passing by reference is the default in Visual
  Basic.

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Private Sub cmdDisplay_Click() Dim amt As
Single 'Illustrate effect of value of parameter
on value of argument picResults.Cls amt 2
picResults.Print amt Call Triple(amt)
picResults.Print amt End Sub Private Sub
Triple(num As Single) 'Triple a number
picResults.Print num num 3 num
picResults.Print num End Sub
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Private Sub cmdCompute_Click() Dim x As Single,
y As Single 'Display the sum of the two numbers
Call GetNumbers(x, y) Call Add(x, y) End
Sub Private Sub Add(num1 As Single, num2 As
Single) Dim sum As Single 'Display numbers
and their sum picResult.Cls sum num1
num2 picResult.Print "The sum of" num1 "and"
num2 "is" sum End Sub Private Sub
GetNumbers(num1 As Single, num2 As Single)
'Record the two numbers in the text boxes num1
Val(txtFirstNum.Text) num2
Val(txtSecondNum.Text) End Sub
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Passing Arguments By Value

• Only a copy of a variable is passed when an
  argument is passed by value.
• If the procedure changes the value, the change
  affects only the copy and not the variable
  itself.
• Use the ByVal keyword to indicate an argument
  passed by value.
• Sub PostAccounts(ByVal intAcctNum As Integer)
• . . ' Place statements here. .
• End Sub

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Private Sub cmdCompute_Click() Dim x As Single,
y As Single 'Display the sum of the two numbers
Call GetNumbers(x, y) Call Add(x, y) End
Sub Private Sub Add(ByVal num1 As Single, ByVal
num2 As Single) Dim sum As Single 'Display
numbers and their sum picResult.Cls sum
num1 num2 picResult.Print "The sum of" num1
"and" num2 "is" sum End Sub Private Sub
GetNumbers(ByVal num1 As Single, ByVal num2 As
Single) 'Record the two numbers in the text
boxes num1 Val(txtFirstNum.Text) num2
Val(txtSecondNum.Text) End Sub
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Scope of Variables Procedure-level Variables

• The scope of a variable defines which parts of
  your code are aware of its existence.
• Procedure-level variables are recognized only in
  the procedure in which they're declared. These
  are also known as local variables.
• You declare procedure-level variables with the
  Dim or Static keywords
• Dim intTemp As Integer
• Static intPermanent As Integer

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Private Sub cmdDisplay_Click() Dim x As Single
x 2 picResults.Print x Call Trivial
picResults.Print x Call Trivial
picResults.Print x End Sub Private Sub
Trivial() Dim x As Single 'Do something
trivial picResults.Print x x 3
picResults.Print x End Sub
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Private Sub cmdDisplay_Click() Dim x As Single
x 2 picResults.Print x Call Trivial
picResults.Print x Call Trivial
picResults.Print x End Sub Private Sub
Trivial() Static x As Single 'Do something
trivial picResults.Print x x 3
picResults.Print x End Sub
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Form-level Variables

• A form-level variable is available to all
  procedures in the form.
• You create form-level variables by declaring them
  with the Private keyword in the Declarations
  section at the top of the form.
• When a form-level variable is assigned a value in
  a procedure, it retains that value when the
  procedure is exited.

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Dim num1 As Single, num2 As Single Private Sub
cmdDisplay_Click() 'Display the sum of two
numbers num1 2 num2 3 picResults.Cls
Call AddAndIncrement picResults.Print
picResults.Print "num1 " num1
picResults.Print "num2 " num2 End Sub Private
Sub AddAndIncrement() 'Display numbers and
their sum picResults.Print "The sum of" num1
"and" num2 "is" num1 num2 num1 num1 1
num2 num2 1 End Sub