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除了逆波兰式求解 字符串表达式之外,还有其他什么方法来求值?
学习是最好的投资!
不少方法啊 表达式树,两个栈(操作数栈,运算符栈),文法等等
直接贴个以前写过的给你吧。
#include <iostream> #include <boost/algorithm/string/trim.hpp> #include <boost/spirit/include/qi.hpp> #include <boost/spirit/include/phoenix_operator.hpp> typedef double value_t; template <typename Iterator> struct calc_parser : boost::spirit::qi::grammar<Iterator, value_t(), boost::spirit::ascii::space_type> { calc_parser() : calc_parser::base_type(expression) { using boost::spirit::qi::double_; using boost::spirit::qi::_val; using boost::spirit::qi::_1; expression = term [_val=_1] >> *( ('+' >> term [_val=_val+_1]) | ('-' >> term [_val=_val-_1]) ) ; term = factor [_val=_1] >> *( ('*' >> factor [_val=_val*_1]) | ('/' >> factor [_val=_val/_1]) ) ; factor = double_ [_val=_1] | '(' >> expression [_val=_1] >> ')' | ('+' >> factor [_val=_1]) | ('-' >> factor [_val=-_1]) ; } boost::spirit::qi::rule<Iterator, value_t(), boost::spirit::ascii::space_type> expression; boost::spirit::qi::rule<Iterator, value_t(), boost::spirit::ascii::space_type> term; boost::spirit::qi::rule<Iterator, value_t(), boost::spirit::ascii::space_type> factor; }; int main() { using boost::spirit::ascii::space; typedef std::string::const_iterator iterator_type; calc_parser<iterator_type> calc; std::string line; while (std::getline(std::cin, line)) { boost::trim(line); if(line=="quit") break; iterator_type first=line.cbegin(); iterator_type last=line.cend(); value_t v; bool r=phrase_parse(first, last, calc, space, v); if (r && first==last) { std::cout << v << std::endl; } else { std::cout << "Parse error" << std::endl; } } return 0; }
这个我也不懂,帮不了你
不少方法啊 表达式树,两个栈(操作数栈,运算符栈),文法等等
直接贴个以前写过的给你吧。
这个我也不懂,帮不了你