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Expression Evaluation using Stacks
Bid Request Id: 25974
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Posted by: |
seatiger74 (25 ratings)
(Software buyer rating 10 )
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Non-action Ratio: |
Very Good - 3.23%
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Buyer Security Verifications: |
Good
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Approved on: |
Aug 31, 2002
11:54:48 AM EDT
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Bidding Closes: |
Sep 2, 2002
12:06:34 PM EDT
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Viewed (by coders): |
293 times
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Deadline: |
9/3/2002
TIME EXPIRED
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Description:
Expression Evaluation using Stacks
First, get the file expr.txt that will serve as your
input. This is a file with each line being an integer algebraic expression
that you will evaluate. Print each expression and its value, one per line.
Setup an ADT Stack type (based on a linked list) so you can have a stack of
integers whenever you need one.
The expressions consist of integer constants and operators +, -, *, /, ( and
). Multiplication and division are to have higher precedence than addition
and subtraction. Generally, a stack is used in this process.
There are 2 main steps in evaluating an expression. First, you need to
translate the expression from infix to postfix. For example, a * (b + c)
is an infix expression whose postfix equivalent is a b c + *. Computers
like postfix expressions because they are VERY easy to evaluate (which is
your second step). To evaluate a postfix expression, setup a stack of ints
and scan the string from left to right. Push any data value onto the stack.
When you see an operator, apply it to the top 2 stack values, pushing the
result back onto the stack. At the end, the top of the stack will be the
value of the whole expression.
First, however you need to translate infix to postfix. A stack is used here
as well. Here is the algorithm:
Scan the infix string from left to right. When you see a digit, collect any
more adjacent digits into one integer value and simply place that value
directly into the postfix string you are building. Other non-blank characters
are handled as follows: (Let c = the character in question):
if c is + - * / or ) then
while stack is not empty and precedence(c) <= precedence(TOS)
pop the stack
add the popped value to the end of the postfix string if not (
end while
if c is not ) then
push c onto stack
else
if stack is not empty, pop it
end if
if c is (, just push it.
After you are done scanning the infix string, you need to pop remaining
operators off the stack, as with
while stack not empty
pop the stack
add the popped value to the end of the postfix string if not (
end while
The 'precedence' function is just an int returning function that you write.
It takes a char c input parameter and bascially returns
1 if C is + or -, 2 if c is * or / and 0 if c is anything else.
Deliverables:
Complete and fully-functional working program(s) in executable form as well as complete source code of all work done.
Complete copyrights to all work purchased.
Platform:
Please write this program in C++, I use the Visual C++ 6.0 to compile and run it.
Must be 100% finished and received by buyer on:
Sep 3, 2002 EDT
Deadline legal notes: All times are expressed in the time zone of the site EDT (UT - 5). If the buyer omitted a time, then the deadline is 11:59:59 PM EDT on the indicated date.
Special Conditions / Other:
please deliver the codes ontime
Additional Files:
This bid request includes IMPORTANT additional attached files. Please download and read fully before bidding.
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Bidding/Comments:
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Bid Amount
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Coder Rating |
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This bid was accepted by the buyer!
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$20 (USD)
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Aug 31, 2002
12:42:49 PM EDT
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8.2
(Very Good)
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Hello Seatiger74,
I have done several academic assignments like this.So i may please be given a chance.I will finish the work to your full satisfaction.
You have given chance to so many coders.So i eagerly expect that you would give me a chance too to prove my caliber.
Regards,
V.Lakshmi Narasimhan
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