Thread: Just a postfix clarification.

With negative numbers ( using a unary '-' ), such as the examples:

-6(5+3)/2
(5+3)*(-2+1)

How is this converted to postfix? I haven't really tackled the issue too deep but it seems like it may interfere with a minus in postfix. I'd wager a guess that these would be converted as:

6-53+*2/
53+2-1+*

But in evaluating the second one, I could see myself ending up with a loose end at 7*. I hope you're following. If you know how these are handled, please tell me. Perhaps I should put parenthesis in the postfix such as:

(-6)52+*2/
53+(-2)1+*

Any suggestion or answers on how this is handled? The way my program is set up, it's currently accepting a string, converting to a postfix string and evaluated to a long. Thanks.

Another possiblility I'm considering is that in the postfix string the instance unary '-' is replaced with another character. Perhaps a tilde or something similar.

EDIT: Actually I think I got it. Since I'll have to add spaces to accomedate two digit numbers, I'll just have to do a check in converting to postfix to see if a '-' is unary and then just not add a space for that. Example:

Code:

-34(16+22)/2          /* infix */
-34 16 22 + * 2 /     /* postfix */

If you can think of something better or you think this is the best way, some input would be great.

(5+3)*(-2+1)

5 3 + 2 Uminus 1 + *

edit: sry, didnt read your post carefully, so i guess your problem is with ambigous symbols. simply resolve them by defining a unique symbol for them:
"-" (binary minus) becomes the symbol "-"
"-" (unary minus) becomes the symbol "Uminus"