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POParsing a chemical formula from a string in C#?
 

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  1. POParsing a chemical formula from a string in C#?
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    <p>I am trying to parse a chemical formula (in the format, for example: <code>Al2O3</code> or <code>O3</code> or <code>C</code> or <code>C11H22O12</code>) in C# from a string. It works fine unless there is only one atom of a particular element (e.g. the oxygen atom in <code>H2O</code>). How can I fix that problem, and in addition, is there a better way to parse a chemical formula string than I am doing?</p> <p>ChemicalElement is a class representing a chemical element. It has properties AtomicNumber (int), Name (string), Symbol (string). ChemicalFormulaComponent is a class representing a chemical element and atom count (e.g. part of a formula). It has properties Element (ChemicalElement), AtomCount (int).</p> <p>The rest should be clear enough to understand (I hope) but please let me know with a comment if I can clarify anything, before you answer.</p> <p>Here is my current code:</p> <pre><code> /// &lt;summary&gt; /// Parses a chemical formula from a string. /// &lt;/summary&gt; /// &lt;param name="chemicalFormula"&gt;The string to parse.&lt;/param&gt; /// &lt;exception cref="FormatException"&gt;The chemical formula was in an invalid format.&lt;/exception&gt; public static Collection&lt;ChemicalFormulaComponent&gt; FormulaFromString(string chemicalFormula) { Collection&lt;ChemicalFormulaComponent&gt; formula = new Collection&lt;ChemicalFormulaComponent&gt;(); string nameBuffer = string.Empty; int countBuffer = 0; for (int i = 0; i &lt; chemicalFormula.Length; i++) { char c = chemicalFormula[i]; if (!char.IsLetterOrDigit(c) || !char.IsUpper(chemicalFormula, 0)) { throw new FormatException("Input string was in an incorrect format."); } else if (char.IsUpper(c)) { // Add the chemical element and its atom count if (countBuffer &gt; 0) { formula.Add(new ChemicalFormulaComponent(ChemicalElement.ElementFromSymbol(nameBuffer), countBuffer)); // Reset nameBuffer = string.Empty; countBuffer = 0; } nameBuffer += c; } else if (char.IsLower(c)) { nameBuffer += c; } else if (char.IsDigit(c)) { if (countBuffer == 0) { countBuffer = c - '0'; } else { countBuffer = (countBuffer * 10) + (c - '0'); } } } return formula; } </code></pre>
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    1. USJake Petroules
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    1. COWhy are you checking whether the first character of the formula is upper case on every iteration of the `for` loop (`!char.IsUpper(chemicalFormula, 0)`)? The index here is always `0`.
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      1. USPieter van Ginkel
    2. COI think your function also has problem with something like C4O2 is this true?
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      1. USSaeed Amiri
    3. COSee also the page http://stackoverflow.com/questions/2974362/parsing-a-chemical-formula/3742985 . It asks for one in Java, with an answer in Python, and links to more complex ANTLR and Python solutions.
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      1. USAndrew Dalke
 

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