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Left-bracket problem in a string
Posted: Thu May 01, 2003 1:38 am
by ^OO^
Hi y'all
I have come across a wierd problem in string disection.
I wrote this bit of code to illustrate it ...
Please notice that math_b has a pair of brackets.
See what this does to the output!
Code: Select all
; Disect a string into its constituent parts for parsing ...
Dim s.s(64) ; hold the parts in this array
Global c.s
Global math_a.s
Global math_b.s
; setup example srings ...
math_a="14.582*3.2/4.5-625+10.1*17.2/13.4-25.123"
math_b="14.582*3.2/4.5-(625)+10.1*17.2/13.4-25.123"
Procedure Test(M.s)
For i=0 To 63
s(i)=""
Next
n=0
For i=1 To Len(M)
c=Mid(M,i,1)
If c="*" Or c="(" Or c="/" Or c=")" Or c="+" Or c="-"
n+1
s(n)=c
n+1
Else
s(n)=s(n)+c
EndIf
Next
WriteString(Chr(10)+Chr(10)+M+Chr(10)+Chr(10))
n=0
While s(n)>""
WriteString(":"+s(n)+","+Chr(10))
n+1
Wend
EndProcedure
; make an output file for the results ...
r=CreateFile(1,"output.txt")
Test(math_a)
Test(math_b)
CloseFile(1)
End
It is holding up my efforts to produce a math expression parser.
Is this a bug?
Is it deliberate for some purpose?
Can anyone see a way round it?
Posted: Thu May 01, 2003 2:44 am
by Pupil
You create a hole in the array(i.e. an empty string) whenever you encounter two reserved characters in a row, this makes your save routine fail...
Posted: Thu May 01, 2003 3:23 am
by ^OO^
Hi Pupil,
this makes your save routine fail...
This problem is not confined to saving.
Try windowing it in a string gadget.
I wrote the little demo to show what happens when I try to separate a string into characters for analysis.
Can you suggest a way of storing and manipulating strings that contain brackets?
Posted: Thu May 01, 2003 4:06 am
by Paul
I think that your logic is a bit wrong.
Try changing this part of your procedure:
Code: Select all
n=0
While s(n)>""
WriteString(":"+s(n)+","+Chr(10))
n+1
Wend
to this:
Code: Select all
For tmp=0 To n
WriteStringN(":"+s(tmp)+","+Chr(10))
Next
Maybe now you see your problem?
Posted: Thu May 01, 2003 6:25 am
by ^OO^
Hi Paul,
I am pretending that the two math strings are unpredictable user input.
The reason I did it the way I did it was that the strings break into irregular sized chunks.
This means that the number of instances of s() cannot be known in advance.
For instance, "14.582" is one chunk. it is six chars long. "*" is another chunk, a smaller one.
None of this is touching on the point ...
This whole thing as about the peculiar problem presented by "(" and ")".
Why don't you mess around with this code and make math_b print out as neatly as math_a?
If you find, as I have, that this is not possible, perhaps you can pin down the reason?
Should you succeed in either of these outcomes, I shall be intensely interested as,
so far, the solution has eluded me.
Posted: Thu May 01, 2003 11:09 am
by Pupil
I told you what the problem was, just change your save routine to this and say otherwise :)
Code: Select all
While n<64
If s(n) <> ""
WriteString(":"+s(n)+","+Chr(10))
EndIf
n+1
Wend
Before you had this:
what do you think happend when an empty string is in s(n)? -The loop will stop.
Why is there an empy string in the middle of the array? -It's because when two control characters('+-*/()') is encountered in a row your routine jumps one instance extra (n+1) without storing something in the array and thus effecively creating a hole in the array...
Posted: Thu May 01, 2003 8:22 pm
by ^OO^
Hi, Pupil
I wrote it the way I wrote it to demonstrate the problem. Having the output terminate prematurely shows the problem and where it occours.
I NEED to store these charaters, individally, in the array, not leaving any blanks. Not just to print them. I need the array to be intact so that I can do the math expression parsing. This 'control character' behavior is a major obstruction.
Oooh. I just had a thought. Must do an experiment. I'll tell you what happens ===>
Ah ha! It worked - a little for-next loop to remove the blanks.
Onwards!