ExpressionEvaluator.h

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#pragma once
 
#include <iostream>
#include <string>
#include <algorithm>
#include <unordered_map>
#include <cwctype>
#include <cmath>
#include <stdexcept>
 
class ExpressionEvaluator {
 
    std::wstring expression;
    std::unordered_map<std::wstring, double> variables;
    size_t pos;
    std::wstring token;
    std::wstring lastError;
    enum class TokenType { NONE, NUMBER, VARIABLE, OPERATOR, LPAREN, RPAREN, END } tokenType;
 
public:
 
    bool compile(const std::wstring& expr);
    bool evaluate(const std::unordered_map<std::wstring, double>& vars, double& result);
    std::wstring getLastError();
 
private:
 
    void skipWhitespace();
 
    std::wstring toLowerCase(const std::wstring& input);
 
    bool nextToken();
    bool expect(TokenType expectedType, const std::wstring& expectedToken = L"");
    bool parseExpression(double& result);
    bool parseTerm(double& result);
    bool parseFactor(double& result);
    bool parsePrimary(double& result);
};