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POEquation (expression) parser with precedence?
 

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  1. POEquation (expression) parser with precedence?
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    <p>I've developed an equation parser using a simple stack algorithm that will handle binary (+, -, |, &amp;, *, /, etc) operators, unary (!) operators, and parenthesis.</p> <p>Using this method, however, leaves me with everything having the same precedence - it's evaluated left to right regardless of operator, although precedence can be enforced using parenthesis.</p> <p>So right now "1+11*5" returns 60, not 56 as one might expect.</p> <p>While this is suitable for the current project, I want to have a general purpose routine I can use for later projects.</p> <p><strong>Edited for clarity:</strong></p> <p>What is a good algorithm for parsing equations with precedence?</p> <p>I'm interested in something simple to implement and understand that I can code myself to avoid licensing issues with available code.</p> <p><strong>Grammar:</strong></p> <p>I don't understand the grammar question - I've written this by hand. It's simple enough that I don't see the need for YACC or Bison. I merely need to calculate strings with equations such as "2+3 * (42/13)".</p> <p><strong>Language:</strong></p> <p>I'm doing this in C, but I'm interested in an algorithm, not a language specific solution. C is low level enough that it'll be easy to convert to another language should the need arise.</p> <p><strong>Code Example</strong></p> <p>I posted the <a href="http://www.ubasics.com/simple_c_equation_parser" rel="noreferrer">test code for the simple expression parser</a> I was talking about above. The project requirements altered and so I never needed to optimize the code for performance or space as it wasn't incorporated into the project. It's in the original verbose form, and should be readily understandable. If I do anything further with it in terms of operator precedence, I'll probably choose <a href="https://stackoverflow.com/questions/28256/equation-expression-parser-with-precedence/783132#783132">the macro hack</a> because it matches the rest of the program in simplicity. If I ever use this in a real project, though, I'll be going for a more compact/speedy parser.</p> <p><strong>Related question</strong> </p> <blockquote> <p><a href="https://stackoverflow.com/questions/114586/smart-design-of-a-math-parser">Smart design of a math parser?</a></p> </blockquote> <p>-Adam</p>
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    1. COI have writen an [expression parser in C#](http://www.guge.net/?p=3#more-3) on my blog. It does infix to postfix without the stack in the shunting yard algorithm. It only uses an array.
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    2. COAs i understand you need parse only arithmetic expression. Use [Reverse Polish Notation](http://en.wikipedia.org/wiki/Reverse_Polish_notation)
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