result of a mathematical formula

coma · Post by **coma** » Mon Dec 11, 2006 3:12 am

Hi everybody.

In my program I have mathematical expressions in strings, for example a$="200+100/2"

How can I put the result of the operation into a numeric variable ? Does anyone know a procedure to do this ?

It seems very difficult to me, especially because of priority of operators.

Froggerprogger · Post by **Froggerprogger** » Mon Dec 11, 2006 8:38 am

Have a look at these three. keyword: expression parser:

http://www.purebasic.fr/english/viewtopic.php?t=15762

http://www.purebasic.fr/english/viewtopic.php?t=17371

http://www.purebasic.fr/english/viewtopic.php?t=15845

PB · Post by PB » Mon Dec 11, 2006 10:50 am

And there's also these two shorter versions:

http://www.purebasic.fr/english/viewtopic.php?t=24836
http://www.purebasic.fr/english/viewtopic.php?t=24921

netmaestro · Post by **netmaestro** » Mon Dec 11, 2006 1:16 pm

You can also tap into the windows scripting host:

Code: Select all

Procedure.d Evaluate(exp.s)
  If CreateFile(0,"tmp.vbs")
    WriteStringN(0, "wscript.stdout.writeline "+exp) : CloseFile(0)
    prg=RunProgram("wscript"," tmp.vbs",GetCurrentDirectory(),#PB_Program_Open|#PB_Program_Read)
    If prg
      result.d = ValD(ReadProgramString(prg))
      CloseProgram(prg)
      ProcedureReturn result ; success
    Else
      ProcedureReturn 0 ; scripting host failure
    EndIf
  Else
    ProcedureReturn 0 ; CreateFile failure
  EndIf
EndProcedure

Debug Evaluate("47+2*10/3")

which is probably the shortest and most powerful solution. The scripting host can do anything VBScript is capable of, which is quite a lot.

Trond · Post by **Trond** » Mon Dec 11, 2006 1:31 pm

You forgot CloseProgram()

netmaestro · Post by **netmaestro** » Mon Dec 11, 2006 1:36 pm

Quite right, thanks for pointing it out. Should be reasonably correct now. Also, it doesn't seem to need #PB_Program_Hide.

PB · Post by PB » Mon Dec 11, 2006 1:40 pm

> Should be reasonably correct now

Well, technically the "If prg" block should go inside the "If CreateFile" block,
because if the file was never created then there's no need to do an "If prg"
check.

Also, I'd make the code create the file in the TEMP dir, so the user
is never aware of it.

netmaestro · Post by **netmaestro** » Mon Dec 11, 2006 1:43 pm

No, you have to make a separate check, to cover two eventualities: couldn't create the file, couldn't load the scripting host. Agreed on the TEMP dir though, good idea. I'm also looking to see if I can stream the command line into the host, no file needed. Should be doable, if anyone knows how, pls post before I spend a lot of time on it

PB · Post by PB » Mon Dec 11, 2006 1:48 pm

> two eventualities: couldn't create the file, couldn't load the scripting host

Yes, but if CreateFile fails, there's no need to check "prg". But if CreateFile
worked, then you can go ahead and check "prg" in the same block, so both
cases are covered with only one decision and not two.

Here's two "Visustin" flowcharts to show what I mean:

http://img15.imgspot.com/?u=/u/06/344/19/Image11165881937.gif

netmaestro · Post by **netmaestro** » Mon Dec 11, 2006 1:52 pm

You win. It does have a cleaner feel to it. Updated.

Helle · Post by **Helle** » Mon Dec 11, 2006 2:03 pm

Not nice, but the result is correct (PB 4.0 or higher):

Code: Select all

Debug ValD(StrD((ValD("47") + ValD("2") * ValD("10") / ValD("3"))))

Gruss
Helle

coma · Post by **coma** » Mon Dec 11, 2006 2:40 pm

thank you all for the replies, it will help me a lot.

PB · Post by PB » Tue Dec 12, 2006 12:17 am

@TheFool: I changed my link, just for you, to use ImgSpot to avoid the ads.