I my opinion it is much easier to implement a sort of RPN calc for that.
Also if you have a PC connected to the circuit you may want to do that on
the PC side generating a pcode (with converting the normal form to RPN and
do all possible pre-calculations) so then the PIC needs only a much lighter
pcode engine rather than a more complex parser.

Tamas


On Thu, Apr 23, 2009 at 12:54 PM, Isaac Marino Bavaresco <
isaacbavaresco@yahoo.com.br> wrote:

> Nice code!
>
> Out of curiosity I downloaded your code and tried to compile with
> Hi-Tech PICC.
>
> The function 'calc_number' calls itself  recursively because of the NOT
> operator, so I commented it out. I had to do other minor PIC specific
> changes.
>
> Compiled and run OK.
>
> Occupied 2087 words of FLASH and 140 bytes of RAM in a PIC16F648A.
>
> It calculates "(123+234)*34" in 11.89ms @ 20MHz.
>
> Regards,
>
> Isaac
>
>
> M. Adam Davis escreveu:
> > It took me a lot longer to find mine than I expected!  I posted one
> > simple equation parser here:
> >
> > http://www.ubasics.com/simple_c_equation_parser
> >
> > The code and compiled test executable (windows) can also be
> > downloaded, http://www.ubasics.com/files/equation.zip
> >
> > It uses a stack method with no operator precedence.  It handles binary
> > operators (+, -, *, /, |, &, ^), unary operators(!), parenthesis((,)),
> > and numbers.  Parenthesis can be used to force precedence, everything
> > else is strictly left to right evaluation.
> >
> > You'll need to add < and > binary operators (and, or, not, xor,
> > already exist), and you'll need to either add symbols to represent
> > your inputs, or modify the parse routine to accept characters and use
> > the correct variable when a word occurs in the equation.
> >
> > You'll also need to instruct users to use parenthesis rigorously:
> >
> > T1>T2&T1>72 becomes (T1>T2)&(T1>72)
> > T1>T2+5&T2<32 becomes (T1>(T2+5))&(T2<32)
> >
> > The program I posted compiles under tcc (tiny c compiler) and should
> > be standard ansi C, so it ought to port fine.  Of course you'll need
> > to remove the example main() at the bottom, and perhaps the odd
> > debugging printf scattered through the code (I believe they are all
> > commented out...).
> >
> > Good luck, let me know how it works out, and if you do add the ability
> > to use variables and <, > operators, feel free to send me the code and
> > I'll drop it on the website for others.
> >
> > -Adam
> >
> > On Wed, Apr 22, 2009 at 9:26 PM, Forrest W Christian <forrestc@imach.co=
m>
> wrote:
> >
> >> I've got a temperature control application where I'd like to be able to
> >> let the customers enter expressions (via serial) like:
> >>
> >> T1>T2&T1>72
> >>
> >> or
> >>
> >> T1>T2+5&T2<32
> >>
> >> Where T1 and T2 are temperature readings from a thermocouple.   The
> >> result of these expressions will be used to turn on and off fans and/or
> >> heaters in an application I am working on.   I could hardcode a lot of
> >> options, but I think some simple customer-modfiable rules would be best
> >> in this particular application.
> >>
> >> So, before I write my own parser and the like I figured I'd ask if
> >> there's code out there which would be suited for this, and is small (t=
he
> >> target is a PIC16F886 and CCS C - and it's not easy to change it in th=
is
> >> application).
> >>
> >> I've found some example code but it's all overly big and not well suit=
ed
> >> to what I'm looking for.    I know how to write this myself, but I'd
> >> rather just use some existing code - or perhaps hear some other ideas.
> >>
> >> Oh, I really only need a few variables (I'll probably use TA, TB inste=
ad
> >> of T1, T2 just to simplify parsing), a few boolean functions (and, or,
> >> greater than, less than, maybe >=3D or <=3D), and possibly addition,
> >> subtraction, and less possibly multiplication and/or division.
> >>
> >> -forrest
>
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