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Understanding and Using Visual Basic Part 4
By: Jared Hoylman -
Advanced String Parsing
In the last
article we showed the four major string parsing functions along with a few
simple examples. In this article we are going to kill two birds with
one stone. PBASIC is not very friendly when it comes to conditional
statements. Without the If...ElseIf...Else...EndIf kind of conditional
statements, beginners find it difficult to program a Basic Stamp to do exactly
what they want. If the PBASIC language had the If...ElseIf...Else...EndIf
kind of conditional statements I believe it would be much easier for beginners
to learn and program the Basic Stamp. So in this article we are going
to use our VB string parsing functions to make a complete application that
will manipulate true If...ElseIf...Else...EndIf VB style conditionals
into functioning PBASIC code..!
Lets take
for example a VB type If conditional...
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If [Condition1=True]
Then
DoCode#1
ElseIf [Condition2=True]
Then
DoCode#2
Else
DoCode#3
End If
|
This could
be transformed into PBASIC code by doing the following...
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If [Condition1=True]
Then DoCode1
If [Condition2=True]
Then DoCode2
DoCode#3
EndIf:
' End of Main Program
' Start Extra Subs
DoCode1:
DoCode#1
Goto EndIf
DoCode2:
DoCode#2
Goto EndIf
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This code
would flow the exact same way as the VB typeIf conditional, only it looks
a little more complex...
Creating
The VB Program
Now you need
to open up a New Standard EXE project. Add two labels (Label1 and
Label2), two Textboxes (txtVB and txtPBASIC), and a command button (cmdConvert)
to your form. Your form should look like the one below...
Now we need
to set a few properties before we continue...
txtVB
and txtPBASIC
Multiline = True
ScrollBars = 2 - Vertical
Text = "" ("" means nothing)
cmdConvert
Caption = "Convert"
And you can change the Label captions to whatever you wish.
How To
Go About It
OK. The
easiest way that I can think of doing it would be to loop through every line
one at a time in the VB type code and convert it to the PBASIC type code.
So we need a function to extract a specific line from txtVB. I went
ahead and wrote one for you. It is a little confusing if you are not experienced
in VB programming so I added LOTS of comments to help you out. Add This
code to your form.
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Private
Function GetLineText(txtBox As TextBox,
_
lLine
As Long
) As String
Dim x As
Long
Dim sText As
String
' Holds Textbox Text
Dim lLineStart
As Long '
Chr That Begins Line
Dim lLineEnd As
Long
' Chr That Ends Line
Dim lLength As
Long
' Length of line
sText = txtBox.Text
' We need to make sure that the text ends
in a
' vbCrlf so...
If Right$(sText, 2) <> vbCrLf
Then
sText = sText & vbCrLf
End If
' If you want the first line of the textbox
you
' know that the first character of the
line
' will be the first character of the TextBox.
If lLine = 1 Then
lLineStart = 1
Else
' If it isn't line 1 then we must find
the first
' character of the line. We
know that each line
' is seperated by a vbCrLf (carriage return
and
' line feed). So to find the second line
starting
' position we find the 1st vbCrLf. And
to find
' the end of the second line we find the
3rd
' vbCrLf.
' This next little bit of code finds each
vbCrlf
' up to (lLine - 1) which is the one that
we need.
lLineStart = 1 ' Initialize
Offset
For x = 1
To lLine - 1
lLineStart = InStr(lLineStart, sText, vbCrLf)
' Compensate for the 2 characters
in vbCrLf
lLineStart = lLineStart + 2
Next x
End If
' Now we need to find the end of the line. We
' know that it is the very next vbCrLf
after
' lLineStart, so...
lLineEnd = InStr(lLineStart, sText, vbCrLf)
' Get Line Length
lLength = lLineEnd - lLineStart
' Now we have the starting and ending characters
' for the line that we are trying to find. Do
' you remember the Mid$ statement from
the
' previous article..?
GetLineText = Mid$(sText, lLineStart, lLength)
End Function
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OK. Now with
that out of the way we need to discuss how we are going to convert the VB
code to PBASIC code. Lets take the example code that I gave above.
|
If [Condition1=True]
Then
DoCode#1
ElseIf [Condition2=True]
Then
DoCode#2
Else
DoCode#3
End If
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And the PBASIC
equivalent...
|
If [Condition1=True]
Then DoCode1
If [Condition2=True]
Then DoCode2
DoCode#3
EndIf:
' End of Main Program
' Start Extra Subs
DoCode1:
DoCode#1
Goto EndIf
DoCode2:
DoCode#2
Goto EndIf
|
Really it's
not that difficult to do. If a line is like If [condition] Then or
ElseIf [condition] Then we simple copy the line and add a
Label to the end of the line. All of the code in between these statements
gets put into a subroutine at the end of the program. If we find that a
line equals Else then we simply copy the rest of the lines of code
as they are. And finally if a line equals End If then we convert
it to the Label EndIf:.
But first
we need to go over another very useful string operator. It is the Like
operator. The Like operator is used to compare two strings, usually
using wildcards. So lets see an example...
|
Dim bResult
As Boolean
bResult = "If X=1 Then" Like "If * Then"
|
In this example
bResult would equal True because the wildcard *
can be any number of characters, so the pattern matches.
So with that
out of the way here is the core part of the program. Again I added TONS of
comments.
|
Private
Sub cmdConvert_Click()
Dim sLine As
String
' Holds the line text
Dim sPBASIC As
String ' Hold
converted string
Dim sSubs As
String
' Hold subroutines
Dim lLabelCount
As Long ' Unique label
counter
Dim lCurrentLine
As Long
' Current Line
Dim sCurrentLabelText
As String
Dim bSubInitialized
As Boolean
Dim bMakingElse
As Boolean
Dim lSubsAdded
As Long '
Counts subs added
' We will simply loop through every line
of txtVB
' until we find a line that equals "End
If"
lCurrentLine = 0 ' Initialize
line counter
lLabelCount = 0 ' Initialize
the label count
Do
lCurrentLine = lCurrentLine + 1 ' Get next line
' Get current line text
sLine = GetLineText(txtVB, lCurrentLine)
' Convert line to lowercase for comparison
reasons
sLine = LCase(sLine)
' remove all leading and trailing spaces
sLine = Trim(sLine)
If sLine Like "if * then"
Then
' we have a line like "If [Condition}
Then
' Increment LabelCount and set
label name
lLabelCount = lLabelCount + 1
sCurrentLabelText = "Label" & lLabelCount
' Add the line
sPBASIC = sPBASIC & sLine
' Then add the label and a vbCrLf
sPBASIC = sPBASIC & " " & sCurrentLabelText
sPBASIC = sPBASIC & vbCrLf
' We are now making a subroutine
bSubInitialized = False
ElseIf sLine Like "elseif * then"
Then
' we have a line like "ElseIf
[Condition} Then
' we also need to take off the
first 4 letters
' of the line to be vaid PBASIC
sLine = Right$(sLine, Len(sLine) - 4)
' Increment LabelCount and set
label name
lLabelCount = lLabelCount + 1
sCurrentLabelText = "Label" & lLabelCount
' Add the line
sPBASIC = sPBASIC & sLine
' Then add the label and a vbCrLf
sPBASIC = sPBASIC & " " & sCurrentLabelText
sPBASIC = sPBASIC & vbCrLf
' We are now making a subroutine
bSubInitialized = False
ElseIf sLine = "else"
Then
' we are now making the Else
Part
' set the flag = True
bMakingElse = True
ElseIf sLine = "end if"
Then
' simply add the "EndIf:" label
sPBASIC = sPBASIC & "EndIf:" & vbCrLf
' we are done so exit the loop
Exit
Do
ElseIf bMakingElse =
True Then
' simply copy the lines
sPBASIC = sPBASIC & sLine & vbCrLf
ElseIf bSubInitialized =
False Then
bSubInitialized = True
' if this is not the first sub then we
need to
' end the previous sub
If lSubsAdded > 0
Then
sSubs = sSubs & "Goto
EndIf" & vbCrLf
sSubs = sSubs & vbCrLf
End
If
' Increment counter
lSubsAdded = lSubsAdded + 1
' Now add the new sub name and the current
line
sSubs = sSubs & sCurrentLabelText & ":"
sSubs = sSubs & vbCrLf
sSubs = sSubs & sLine & vbCrLf
Else
' none of the other criteria
above were met so
' we must be adding the line
to the end of the
' Subroutines
sSubs = sSubs & sLine & vbCrLf
End If
Loop
' Do next line
' We found the last line and exited the
loop
' so now we must END the program and finish
up
' the subroutines
sPBASIC = sPBASIC & "End" & vbCrLf & vbCrLf
If lSubsAdded > 0
Then
' subs were added so we need
to end them
sSubs = sSubs & "Goto EndIf" & vbCrLf
End If
' Now we just have to combine sPBASIC and
sSubs
' and show them in txtPBASIC
txtPBASIC = sPBASIC & sSubs
End Sub
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I know that
is really long, but if you take your time and go through the code line by
line it is not that hard to figure out the concept that is being used. If
you just can't figure it out or just want to download the project already
made...then click here.
Be sure to
try it out as it might make programming you Basic Stamp just a little bit
easier. And if you study this code and fully understand it, you are on your
way to becoming a very good VB programmer. ;-)
Limitations
This code
does have some limitations..!
- You can not nest If blocks
- There is no error checking. Try typing "End If" as "EndIf" and see what
happens.
- There is no syntax checking. You can type anything you want in between
the "If" lines and it will copy them anyways.
Anyways I
hope that you learn something from this article. There are a lot of neat
little tricks in this code that took me years to figure out. Learn from
someone that has learned the hard way and make it easy on your self. ;-)
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