Writing in postfix notation

This is a discussion on Writing in postfix notation within the C++ Programming forums, part of the General Programming Boards category; For a lab we must convert an infix expression to a postfix one that is devoid of parentheses. Like if ...

  1. #1
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    Writing in postfix notation

    For a lab we must convert an infix expression to a postfix one that is devoid of parentheses.

    Like if I entered (3 + 5) the postfix expression is 35+

    However, what if I do (19 + 2)? It certainly is not 192+, for that would make 111, which just... isn't right. And we can't do (19)2+ I assume because the problem clearly states that parenthesis cannot be used. What's the official way, here?

  2. #2
    Programming Sex-God Polymorphic OOP's Avatar
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    You're probablly reading the problem wrong. You can't do what you want to do.

    EDIT: You are talking about compile-time, right? Or are you saying that you want someone to input something through IO? You can't overload operators to make 35+ do 3 + 5 because there is no postfix operator +

    If you mean via IO then I don't see what the problem is. Just use a space.
    Last edited by Polymorphic OOP; 11-30-2002 at 10:23 PM.

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    I think you misread the question

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    The user inputs a string of an infix expression and the equation inputted into the string is converted to postfix and evaluated

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    why not just put spaces or commas in between the numbers? so 3+5 -> 3,5+ or 3 5+, and 19 + 2 -> 19,2+ or 19 2+
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  6. #6
    Programming Sex-God Polymorphic OOP's Avatar
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    Yeah, like i said

    35+

    is not a postfix addition expression because it has only one operand

    you have to separate them by spaces.

    IE

    3 5 +

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    Ah, I see :P

    Yeah, in our class 3 + 5 is written as 35+

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    Well what you can do is enter all those character into a char array infix, then convert it into a postfix expression and put it into char array postfix, then evaluate that postfix expression using the postfix array.

    I did the same thing, and I used a Stack data structure to solve it, with a dynamic char array to hold my postfix expression.

    Also you need to put spaces netween your postfix expression, because it makes it easier to read, for example:

    192+ --> is this (19 + 2) or (1 + 92) ?

    so you write it:

    19 2 +

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