ummm...... how to evaluate the formulae??

[Mars]

if I want to write a program to evaluate a formulae,
what kind of algorithm should I use??

for example,
input:
(2+3)*(3/4)+6-8

how to deal with the brackets??
need to use stacks??

Thx.......




?_?

 

[Lew Pitcher]

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if I want to write a program to evaluate a formulae,
what kind of algorithm should I use??

for example,
input:
(2+3)*(3/4)+6-8

Google for "recursive descent parser"

how to deal with the brackets??

That's part of what the parser does.

need to use stacks??

Perhaps. Or not, as your implementation requires.

Thx.......




?_?

- --

Lew Pitcher, IT Specialist, Enterprise Data Systems
Enterprise Technology Solutions, TD Bank Financial Group

(Opinions expressed here are my own, not my employer's)
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[Steven]

if I want to write a program to evaluate a formulae,
what kind of algorithm should I use??

for example,
input:
(2+3)*(3/4)+6-8

how to deal with the brackets??
need to use stacks??

You can convert the algebraic expression to reverse polish notation.
Try searching for reverse polish notation. It is very effective with
computational expressions and parenthesis.
Try http://en.wikipedia.org/wiki/Reverse_Polish_notation

 

[Mars]

Steven mentioned:

You can convert the algebraic expression to reverse polish notation.
Try searching for reverse polish notation. It is very effective with
computational expressions and parenthesis.
Try http://en.wikipedia.org/wiki/Reverse_Polish_notation

icic,
so if I enters
1+3*4+2

it is
1 3 4 * + 2 +

right??

 

[Mars]

Lew Pitcher mentioned:

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Google for "recursive descent parser"




That's part of what the parser does.




Perhaps. Or not, as your implementation requires.

THX~~

 

[infobahn]

icic,
so if I enters
1+3*4+2

it is
1 3 4 * + 2 +

right??

Looks right to me.

 

[sipetar]

if I want to write a program to evaluate a formulae,
what kind of algorithm should I use??

for example,
input:
(2+3)*(3/4)+6-8

how to deal with the brackets??
need to use stacks??

Thx.......




?_?

RPN calculator (reverse polish notation)
I' ve got one implementaion with stach so fi you need it I can send you
by mail..

 

[sipetar]

RPN calculator (reverse polish notation)
I' ve got one implementaion with stach so fi you need it I can send you
by mail..

I mean stack! sorry

 

[Gregory Toomey]

if I want to write a program to evaluate a formulae,
what kind of algorithm should I use??

for example,
input:
(2+3)*(3/4)+6-8

how to deal with the brackets??
need to use stacks??

Thx.......




?_?

Try flex/bison, or write you own lexical analyser & parser.
http://www.gnu.org/software/bison/bison.html

If you dont know the basics of BNF/recursive descent you wont get far.

gtoomey

 

[Eric Sosman]

Mars wrote:




Try flex/bison, or write you own lexical analyser & parser.
http://www.gnu.org/software/bison/bison.html

If you dont know the basics of BNF/recursive descent you wont get far.

These tools are surely overkill for so small a problem.
A stack and a precedence table will do the job just fine
and with less fuss. Two stacks if you want to evaluate at
the same time you're parsing.

 

[Mars]

(e-mail address removed) mentioned:

RPN calculator (reverse polish notation)
I' ve got one implementaion with stack so fi you need it I can send you
by mail..

Great~
my email is : (e-mail address removed)

Thx~