1. Visual Basic 6 Programming.
Lecture 4 : February 2004
Dr. Andrew Paul Myers
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2. Functions.
Functions return a value. So far you have been using inbuilt VB functions, e.g.
sngValue = Sin(sngX_in_rads)
dblPi = 4# * Atn(1#)
VB allows you to write your own! i.e.
dblRad = Radians(dblDegrees)
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3. Writing Functions. General Form:
Private Function <name>( <parameters> ) As <type>
<statement(s)>
<name> = <return value>
End Function
Note : Functions can be Public, i.e. across all forms!!
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4. Example Function 1. Private Function Pi() As Double
‘ A parameterless function to return Pi.
Pi = 4# * Atn(1#)
End Function
************************
‘ Use of this function.
dlbPi = Pi()
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5. Example Function 2.
Public Function Radians(dlbDegrees As Double) _ As Double
‘ Function to convert Degrees to Radians.
Dim dblPi As Double ‘ A local variable.
dlbPi=Pi() ‘ Call Pi function.
Radians = dblPi * dblDegrees / 180#
End Function
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6. Use of Function 2. Dim dlbValue As Double dblValue = Radians(90#)
dblValue = Sin(Radians(90#))
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7. Example Function 3. Public Function Add(intX As Integer, intY As _
Integer) As Integer
‘ Function to add two numbers together.
Add = intX + intY
End Function
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8. Use of Function 3. Dim intResult As Integer
Dim intFirst As Integer, intSecond As Integer
intResult = Add(1, 2) ‘ Not an array!!!
intResult = Add(intFirst, intSecond)
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9. Arrays as Parameters.
Private Function Sum(intValues() As Integer) As Integer
Dim intLoop As Integer, intTotal As Integer ‘ local scope
intTotal = 0
For intLoop = LBound(intValues) To UBound(intValues)
intTotal = intTotal + intValues(intLoop)
Next intLoop
Sum = intTotal
End Function
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10. Subroutines or Procedures.
Functions return a value. Best suited to calculations.
Subroutines/procedures do not, but they can modify the parameters (arguments) passed if required.
Hence “returning” more than one value.
The “Building Blocks” of a program!
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11. Subroutines. General Form: To execute:
Public Sub <name>( <parameters> )
<statement(s)>
End Sub
To execute:
Call <name>( <parameters> )
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12. Writing Subroutines. Public Sub change_text(strText As String)
strText = “It’s been changed!”
End Sub
To call:
Call change_text(strSome_Text)
Again Subs can be Public or Private.
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13. Multiple Forms. Projects can contain more than one Form.
Use the “Add Form” option under the “Project” pull down menu.
Addressing Object/Control Properties:
<Form>.<Object>.<Property> = <Value>
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14. Displaying Multiple Forms.
<Form Name>.Show
<Form Name>.Hide
To speed up Form display times use the Load command in the subroutine Form_Load() on the first Form. e.g.
Private Sub Form_Load()
Load Form2
Load Form3
End Sub
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15. Using Multiple Forms. e.g. Form2.TextBox3.Text = “Hello”
dblValue = Form2.Pi() * 180#
Form2.Show
Form2.Hide
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16. Exiting a Multiple Form Program.
Private Sub Form_QueryUnload(Cancel _
As Integer, UnloadMode As Integer)
Dim AForm As Form
For Each AForm In Forms
Unload AForm
Next
End
End Sub
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