simple calculator in java parser

Question

I am currently making a simple calculator parser in Java, to deal only with + and - operators, and whole numbers. I have read about postfix and infix evaluation, and I am wondering if brackets can be used with either of these methods?

Answer 1

The beauty of the postfix/prefix notation is that you do NOT need the brackets. Brackets are used in infix notation because there are ambiguities, e.g:

a + b - c

This can mean either of the following:

(a + b) - c
a + (b - c)

However, in postfix notation, they are clearly different:

a b + c -
a b c - +

There is no need for parantheses/brackets to enforce evaluation order in postfix notation.

See also

• Wikipedia/Reverse Polish Notation

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Conversion from infix

You can take an expression in infix notation with parantheses and convert it to postfix notation, obeying operator precedence. One such algorithm is Edsger Dijkstra's stack-based "shunting-yard algorithm".

See also

• Wikipedia/Shunting-yard algorithm