stacks and linked lists question,can somebody figure it out please?

[nefsan]

question1



Write a program to process commands as follows.A command can be S(for set) or P(for print),upper or lower case.Each command is on a line by itself ,but can apperar any where on the line.

The S command is followed by two arguments separated by one or more spaces.The first argument is a sssingle letter(upper or lower caese).The scond argument is an arithmetic expression.The command assigns the value of the expression to a single letter variable.Variables are Case-sensitive.(A is different from a).


An expression may include single letter variables ,numeric constants,(with or without decimal point),the binary operators +,-,/,* and the function names ln,exp,sqrt,sin, and cos.If a variable appears in the expression ,then the current value of the variable is used in evaluating the expression.If the expression contains an error (eg mismatched brackets or undefines brackets),a message is printed and the value of the variable to be set reamins unchanged.

the P command is folllowed by a varable,.The value of the variable is printed.

data consists of a series of commands in any order.The commands must be executed in the order given.Data is terminated by the"command",E.It is permitted for the S caomand to be specified by S,s,set,Set,setting variable,etc.(only the first letter is significant);similarly for P


sample data:

S p 24
set r 3.75
s a P+r*21
Set B sin(p+r)*cos(p-r)+p/(r+3.0)
print B
P p
P a
S C (a+B)/(p+r)
set discr B*B -4.0 a*C
PRINT discr
E

[robwhit]

that's not a question. what have you tried so far?

[matsp]

So what exactly are you asking? For us to write your homework?

I would suggest that you make an attempt to write the code, and then post what you've got, and then we can discuss. This is also the "Homework policy" which you could find if you search the forum.

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Mats

[iMalc]

Write a program to process commands as follows

No! I will do nothing of the sort!
The moment I come across an imperative statement like that in a post I immediately ignore it, and I'm sure many others do the same.

Does this look like www.WeDoYourHomeworkForYouNoQuestionsAsked.com ???

[matsp]

No! I will do nothing of the sort!

Are you in a bad mood today?

I think the "Write a program to ... " came directly from the assignment itself, and was not really intended to you or me - but I'm still somewhat confused as to what the original poster actually want us to help with. The title sort of hints that the OP has some clue to how to solve the problem [perhaps], but I'm not sure what he/she wants help with [unless it really _IS_ writing his/her homework of course].

--
Mats

[nefsan]

oh sorry about that- i didnt say what it is i wanted help with!.i do apologise.im studyin for final exams and this question came in a past exam but im not sure how to do it.I am able push and pop onto a linked list.Thats the only thing ive done so far.right now im tryin to break up the problem in parts.i am tryin to write the function that will read the character 's' and set the value to the variable.
like "S p 24" (set p=24) but the other line uses words not just a character. eg set discr.. where discr will be the variable.im not sure how to/cant write the fucntion to read n set the value to the variable when the variable are characeters or words.how can i go about this?

the only code ive written so far works for just pushing and integer onto a stack and popping it out whenever called.should i still post my push and pop code?im workin on my evaluation of the postfix will post it when im finished.i need heplp with the redin and settting of values part please!

[matsp]

Which part of reading & setting a variable do you have a problem with? What have you done so far?

--
Mats

[iMalc]

Yeah I overreacted in my attempt to make a point, sorry. Just never copy and paste something into a thread without adding some of your own words about it.

This is no easy question you're attempting!
You need to start by working out the grammar for the language. For example C looks like this:
http://www.quut.com/c/ANSI-C-grammar-y.html
Have you written a recursive descent parser before?

[Salem]

You need a data structure which associates a word (say "descr") with a value (say 42).
Perhaps a struct containing a string and an int ?

Then perhaps a list / array / tree / hash of these (take your pick), along with functions to say
- find a value given a name
- add a new name/value pair
- update a value