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POCode Golf: Mathematical expression evaluator (that respects PEMDAS)
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copied!<p>I challenge you to write a mathematical expression evaluator that respects PEMDAS (order of operations: parentheses, exponentiation, multiplication, division, addition, subtraction) without using regular expressions, a pre-existing "Eval()"-like function, a parsing library, etc.</p> <p>I saw one pre-existing evaluator challenge on SO (<a href="https://stackoverflow.com/questions/928563/code-golf-evaluating-mathematical-expressions">here</a>), but that one specifically required left-to-right evaluation.</p> <p>Sample inputs and outputs:</p> <pre><code>"-1^(-3*4/-6)" -> "1" "-2^(2^(4-1))" -> "256" "2*6/4^2*4/3" -> "1" </code></pre> <p>I wrote an evaluator in C#, but would like to see how badly it compares to those of smarter programmers in their languages of choice.</p> <h3>Related:</h3> <blockquote> <p><a href="https://stackoverflow.com/questions/928563/code-golf-evaluating-mathematical-expressions">Code Golf: Evaluating mathematical expressions</a></p> </blockquote> <p>Clarifications:</p> <ol> <li><p>Let's make this a function that accepts a string argument and returns a string result.</p></li> <li><p>As for why no regexes, well, that's to level the playing field. I think there ought to be a separate challenge for "the most compact regex".</p></li> <li><p>Using StrToFloat() is acceptable. By "parsing library" I meant to exclude such things as general-purpose grammar parsers, also to level the playing-field.</p></li> <li><p>Support floats.</p></li> <li><p>Support paretheses, exponentiation, and the four arithmetic operators.</p></li> <li><p>Give multiplication and division equal precedence.</p></li> <li><p>Give addition and subtraction equal precedence.</p></li> <li><p>For simplicity, you may assume all inputs are well-formed.</p></li> <li><p>I don't have a preference as to whether your function accepts such things as ".1" or "1e3" as valid numbers, but accepting them would earn you brownie points. ;)</p></li> <li><p>For divide-by-zero cases, you could perhaps return "NaN" (assuming you wish to implement error handling).</p></li> </ol>

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