PREFIX TO POSTFIX help

[hopia]

Are you familiar with prefix and postfix? I just wonder how to solve it especially if the expression is too long. Please help me. thanks.

[stanav]

you need to provide us with more details on what you're trying to do. Give an example. Your question is too vague for anyone to understand what you're asking.

[dbasnett]

As in:

Prefix

and

Postfix

What about

Infix?

[formlesstree4]

I think the OP is wanting to convert Prefix notation to Postfix notation. I don't know how to do that; I've seen examples on converting Infix to Postfix (Shunting yard algorithm anybody?), but I agree with stanav: We need more details to understand what you're really trying to do.

[hopia]

Here is the example:

Input: 5 * 3 + 6 / 2

Output: 5 3 * 6 2 / +

I just wonder how to solve it in VB.NET especially if the expression is too long..

[dbasnett]

I think the OP is wanting to convert Prefix notation to Postfix notation. I don't know how to do that; I've seen examples on converting Infix to Postfix (Shunting yard algorithm anybody?), but I agree with stanav: We need more details to understand what you're really trying to do.

They went somewhere else for the answer, and what they were looking for was the shunting yard.

http://www.dreamincode.net/forums/to...-postfix-help/

[hopia]

up... help me.. please..

[gep13]

up... help me.. please..

hopia,

Rather than simply bumping your thread, which serves of no real help, perhaps you might want to think about providing more information to the problem that you are trying to solve. What have you tried? If it didn't work, why not?

Gary

[cicatrix]

Check out this link:
http://www.chris-j.co.uk/parsing.php

It has a detailed description of the Infix to Postfix notation and later - of the shunting yard algorithm with a step by step example (Java required to view).

[dbasnett]

Check out this link:
http://www.chris-j.co.uk/parsing.php

It has a detailed description of the Infix to Postfix notation and later - of the shunting yard algorithm with a step by step example (Java required to view).

I posted that link in the other forum where the OP asked the same question. I don't think the OP has tried.

[hopia]

I saw the program in the link given above, it is really awesome, I want to to it in visual basic but the problem is I'm having a hard time with an array. I don't know how to use array in a program. hope you can help me please.

[akhileshbc]

Hey,

Here's the C example: http://en.wikipedia.org/wiki/Shuntin...ithm#C_example

Just give it a try to convert it to VB.

[akhileshbc]

This will give you a good start: http://www.homeandlearn.co.uk/net/vbnet.html

Arrays: http://www.homeandlearn.co.uk/net/nets6p1.html

[hopia]

Hey,

Here's the C example: http://en.wikipedia.org/wiki/Shuntin...ithm#C_example

Just give it a try to convert it to VB.

Very nice, Okay I will try it. What is the equivalent of bool, unsigned int, const char in VB??

[cicatrix]

Very nice, Okay I will try it. What is the equivalent of bool, unsigned int, const char in VB??

Boolean, UInteger, Char correspondingly.

[hopia]

how do i convert this in VB?
bool op_left_assoc(const char c)

also this,
int op_preced(const char c)

[hopia]

how do i convert this in VB?
#define is_function(c) (c >= 'A' && c <= 'Z')

[cicatrix]

Just don't try to mindlessly copy and convert the sample code from c++ to vb.net. Even though you can probably end up with something working, it won't probably work as expected.
Instead just understand the algorithm and try to implement it yourself.
1) Tokenize the input string - separate the elements into a number of tokens, for example 1+2/3 will have 5 tokens: 1, +, 2, /, 3.
2) Convert the tokens from infix to postfix, turning 1+2/3 into 1, 2, 3, /, +
3) Implement the Shunting-Yard algorithm to evaluate the postfix queue.

C++ and Vb.Net have enough differences so it would be far better to write your own implementation rather than trying to convert one from C++. From what I see, you don't even try to understand the principle.

Ah, to answer your question

how do i convert this in VB?
#define is_function(c) (c >= 'A' && c <= 'Z')

Private Function is_function(ByVal c As Char) As Boolean
    Return c >= "A"c AndAlso c<= "Z"c
End Function

You can click 'Evaluating Expressions' link in my signature and download the Parser class I made for just the same purpose.