hi guys

so i want help with the concept or idea behind it

using stacks, pop,push,retrieve

can you guys, tell me the concept behind it?

or just the basic idea of it

and after i come to understand how it must work, ill post some codes

please?

thanks

## 3 Replies - 1947 Views - Last Post: 12 February 2010 - 04:37 PM

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**Replies To:** infix to postfix

### #2

## Re: infix to postfix

Posted 12 February 2010 - 09:55 AM

This has probably been posted in the wrong forum!

Infix notation is what we normally use to write down mathematical formula such as 2 + 5. Postfix notation would be 2 5 +. Seen from a computer perspective, infix notation is not very easy to handle, whereas 2 5 + can be accommodated using a stack.

1. Push 2

2. Push 5

3. + (pop 5 pop 2 and add together)

Some programming languages expect their input in postfix notation. FORTH being a prime example.

Hope that helps.

Infix notation is what we normally use to write down mathematical formula such as 2 + 5. Postfix notation would be 2 5 +. Seen from a computer perspective, infix notation is not very easy to handle, whereas 2 5 + can be accommodated using a stack.

1. Push 2

2. Push 5

3. + (pop 5 pop 2 and add together)

Some programming languages expect their input in postfix notation. FORTH being a prime example.

Hope that helps.

This post has been edited by **Martyn.Rae**: 12 February 2010 - 09:56 AM

### #3

## Re: infix to postfix

Posted 12 February 2010 - 04:20 PM

thanks martyn!

im coding this in C++ so i thought this is the right subforum

what i wanted is the idea of a program that

1. reads an input of string (infix)

2. converts that string to postfix (without operating on it)

im coding this in C++ so i thought this is the right subforum

what i wanted is the idea of a program that

1. reads an input of string (infix)

2. converts that string to postfix (without operating on it)

### #4

## Re: infix to postfix

Posted 12 February 2010 - 04:37 PM

Reading the input shouldn't pose too much of a problem - the C++ string and stringstream libraries should be able to help you split a string into tokens (operators/operands)

Take a look at Dijkstra's shunting yard algorithm for the conversion

http://en.wikipedia....-yard_algorithm

It might help to set up a mapping between operators and their precedence - remember that parenthesis are not part of postfix syntax, so they're a special case.

as for stacks, the C++ <stack> library will do everything you need - save you writing your own.

Take a look at Dijkstra's shunting yard algorithm for the conversion

http://en.wikipedia....-yard_algorithm

It might help to set up a mapping between operators and their precedence - remember that parenthesis are not part of postfix syntax, so they're a special case.

as for stacks, the C++ <stack> library will do everything you need - save you writing your own.

This post has been edited by **Bench**: 12 February 2010 - 04:40 PM

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