September 18, 2018
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# Simple Numerical Formula Parser

Environment: VC6 SP3, Windows 95/98/NT/2000

The class CFormulaParser encapsulates a very useful mathematical parser for analytic/numerical formula transformation.

The formula dialog above is actually not necessary for the functionality but allows you comfortable to put in a formula string.

Hereby an extract from the header file:

 ```class CFormulaParser { private: //Implementation CString m_strFormula; CString m_strFunction; CString m_strErrortext; double m_dFktValue; double m_dFunctionConstant[ANZFUNKTKONST]; CStringArray m_strStandardFunction; double SignFactor(WORD& nPosition, CString& strCharacter); double Expression(WORD& nPosition, CString& strCharacter); double SimpleExpression(WORD& nPosition, CString& strCharacter); double Term(WORD& nPosition, CString& strCharacter); double Factor(WORD& nPosition, CString& strCharacter); double Char_n(WORD& nPosition, CString& strCharacter); public: CString GetFormula(); void SetFormula(CString Formula); void SetFunctConst(int index, double val); CFormulaParser(); virtual ~CFormulaParser(); //Interface double Calculation(CString strFormula, double xValue, WORD& ErrorPosition, CString& Errortext); }; ```

The main method in CFormulaParser for the evaluation is:

 ```double Calculation(CString strFormula, double xValue, WORD& ErrorPosition, CString& Errortext); ```

where

• strFormula is the formula string, e.g. "b*sin(x)/x"
• xValue is in this case x, e.g. 3.14 (point instead comma!)
• ErrorPosition gives back the error position in the string
• Errortext gives back the corresponding error text

The parser is part of the program SimplexNumerica. For more information, please see my German website http://www.SimplexNumerica.de.

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