infix , postfix and prefix

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hello , i have this assignment of converting from infix equation to a postfix and prefix in c++ , our teacher gave us the algorithm , but it has been a month and no one could make one , so could you please show me the code of it , i looked for codes in the net , but all of them where using libraries , and i dont want to use them , so please , i need your help ...
with regards ..
ahmed yousify ... :)

Posted 30-Mar-12 10:48am

LifeSmiler

Updated 30-Mar-12 11:02am

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nv3 30-Mar-12 17:00pm

As this is your home work assignment, I think you will be well advised to take yourself a shot at the problem. In this way, you will learn a lot more than letting someone else write some program code for you.

But even taken that aside; what do you mean by "converting from infix to a postfix and prefix"? Are you talking about writing an interpreter or parser? From what you wrote it is not clear to me, what the actual task is?

LifeSmiler 31-Mar-12 4:43am

thanks for your opinion , i meant , if we i have a normal equation that is written as infix , and i want to change it to postfix and prefix ,do u know what i mean ??

Addy Tas 30-Mar-12 18:52pm

I'm wondering if you could be managment material.... trying to make other people work for you is in general not a bad idea. In general also means that sometimes it's a bad idea, homework is needed to learn something. Even if you do not reach the correct answer, you will learn from trying.
Good luck with your assignment and one small remark; don't think to hard, it's really not that complicated. Take it all one step at a time!

LifeSmiler 31-Mar-12 4:46am

thanks for your opinion ,i kind of like your answer , but i really tried but didnt worked out , as i said earlier , all the code that i've seen were using libraries and i dont want that , so if you add a solution to it , i would appreciated it , and if you dont , well thank you any ways ... :)

Addy Tas 31-Mar-12 5:31am

Hi, i think you have already figured out that i'm not going to give you the(as if there would be just one) answer. I would suggest that you post what you have tried and i'll give you hints on what you might want to review.

Sounds ok?

Cheers, AT

Hivi Dino 31-Mar-12 10:05am

Hello ,I have the same problem,I also Need that code :D

Hivi Dino 31-Mar-12 10:44am

Ahmed i wondered when i saw you here :D ,Please Addy Tas Help us We Need your Help,The Algorithm that our Teacher has gave us is Too Little Bit,we can't write the correct code only by that Algorithm,This is The Algorithm that He gave us:
((
Evaluating Postfix Expression:
scan given postfix expression;
for each symbol in postfix
if operand
then push its value onto a stack S;
if operator then
Begin
pop operand2;
pop operand1;
apply operator to compute operand1 op operand2;
push result back onto stack S;
End
return value at top of stack;

Evaluating Prefix Expression :
reverse given prefix expression;
scan the reversed prefix expression;
for each symbol in reversed prefix
if operand then
push its value onto a stack S;
if operator then
begin
pop operand1;
pop operand2;
apply operator to compute operand1 op operand2;
push result back onto stack S;
end if
return value at top of stack;
))

LifeSmiler 1-Apr-12 10:54am

thanks HiVi for the algorithm ... ;)

3 solutions

Solution 2

Before asking question please read this[^]

Posted 30-Mar-12 17:02pm

Pranit Kothari

Solution 1

I found several programs after a search.
Check them to see if they work as you want it to.

http://ds4beginners.wordpress.com/2006/10/18/infix-to-postfix-conversion/[^]
http://www.cfanatic.com/topic2385/[^]
http://www.physicsforums.com/showthread.php?t=159713[^]

Posted 30-Mar-12 16:06pm

«_Superman_»

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Andreas Gieriet · Accepted Answer · 2012-03-31T19:28:00

First, define the problem such that all open items are specified, e.g. you might assume some constraints
- let's define + and - as operator
- let's define double as operand type
- let's assume that the operators and operands are separated by spaces
Now, identify the objects you need
- stack<double> for push/ pop operations
- string to store the initial expression
- string stream that gets initialized by the expression string and that is read (scanned) by the >> operator into individual string symbols
- a while loop that reads the string stream as long as there are symbols available
- a switch in the while loop body that decides on - to do -, on + to do +, and else to convert to double an push to the stack
- after the while block, write the top of the stack to the output
- the "do -" and the "do +" is double a = stack. pop(); double b = stack.pop(); stack.push(a - b); (respectively a+b)
That's it for postfix. E.g. "2 3 + 4 -" results in "1".

For Prefix:
- string with prefix expression
- target that will hold postfix expression
- string stream that gets initialized with prefix expression string
- string that holds the last operator (initially empty)
- while loop that reads in each symbol by >>
- switch for - and +: append space plus the last operator to the target string and store the new operator as last operator. The other values are appende directly to the target string (with a space before the value).
- after the while block, append the last operator to the target string
- finally, call the Postfix function from above on the target string
That's all, folks!

Have fun!
Cheers
Andi