1. Visual Basic 6 Programming.
Lecture 3 : February 2004
Dr. Andrew Paul Myers
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2. Scope of Variables.
So far variables have been local to procedures (subroutines). Could have the same names, but different values.
We can have : Form level variables.
Declare in “Declarations – General”, i.e
with Option Explicit statement.
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3. Scope of Variables. Option Explicit Private intValue as Integer
Public sngRadius as Single
Private Sub Form_Load()
‘ Some VB statements!
End Sub
Private : Form level variable
Public : All forms.
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4. Doing it again & again. So far…
The order VB statements are executed inside a subroutine can be changed using conditional statements.
VB statements can be repeated by using loops (there are several types).
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5. For… Next Loop. General Form: e.g.
For <counter> = <start> To <stop> Step <increment>
<statement(s)>
Next <counter>
e.g.
For intLoop = 0 To 10 Step 1
MyTextBox.SelText = Str(intLoop) & vbCrLf
Next intLoop
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6. Nested Loops. Dim intLoop As Integer Dim sngX As Single
For intLoop = 1 To 10
For sngX = 0# to 10# Step 0.1
<Statement(s)>
Next sngX
Next intLoop
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7. Indeterminate Loops. These do not execute a fixed number of times!
General Form: Do
<statement(s)>
Loop Until <condition(s)>
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8. Do... Until Loop. Dim strPassWord As String Do
strPassWord = _ InputBox(“Password?”)
Loop Until strPassWord = “123”
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9. More Error Checking. <statement(s)> Do
strX = InputBox(“Enter a +ve no.”)
If (IsNumeric(strX) = False) Then strX = “-1”
Loop Until ( Val(strX) > 0 )
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10. More Loops. e.g. Do <statements(s)>
Loop While <condition(s)>
e.g.
<statement(s)>
Loop While ( dblValue < 0# )
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11. Yet More Loops… Do While <condition> <statement(s)> Loop
e.g.
Dim blnProg_Finished As Boolean
blnProg_Finished = False
Do While (blnProg_Finished = False)
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12. Arrays.
An array is a simple structure, capable of storing many variables of the same type in a single data structure.
Declare arrays with other variables.
Arrays can be of any data type.
Scope can be global to a form or local to a procedure, but not global to all forms!
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13. Declaring Arrays. Dim sngValue(6) As Single
This sets up 7 single precision variables called :
sngValue(0)
sngValue(1)
sngValue(2)
sngValue(3)
sngValue(4)
sngValue(5)
sngValue(6)
Each identified by a unique subscript in brackets.
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14. Using Arrays.
After declaration, they can be used in the same way as other variables, but remember the subscript!!! e.g.
Dim intArray(20) As Integer
intArray(1) = 1
intArray(2) = 2
intArray(3) = 3 * intX
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15. Array Storage. intX(0) intX(1) intX(2) intX(3) intX(4)
Arrays can be thought of thus:
e.g. If we have a 5 element array.
Dim intX(4)
intX(0) = 21
intX(1) = 22
intX(2) = 23 etc…
intX(0) intX(1) intX(2) intX(3) intX(4)
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16. Using Arrays. Dim intLoop As Integer Dim intArray(20) As Integer
For intLoop = 0 To 20
intArray(intLoop) = 0
Next intLoop
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17. Using Arrays. Dim intLoop As Integer
Dim dblArray(360) As Double, dblPi As Double
dblPi = 4# * Atn(1#)
For intLoop = 0 To 360
dblArray(intLoop) = Sin(intLoop * dblPi / 180#)
Next dblLoop
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18. More on Arrays. Arrays bounds can be user defined:
Dim strName( 5 To 10 ) As String
Dim sngX( -25 To 25 ) As Single
intValue = LBound(sngX) gives -25
intValue = UBound(sngX) gives 25
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19. Scope of Arrays. Local : Private Sub Form_Load()
Dim strName(20) As String
End Sub
Global : In “General Declarations”.
Option Explicit
Private strName(20) As String
Note : You can not share arrays across forms!
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