状态机学习（五）解析四则运算式

将四则运算拆分成一个个数字和符号后

就进行运算分析

使用以下语法规则:(摘录自《自编编程语言》)

expression：

term：

primary expression:

 

 代码如下:

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#pragma once #include <string> #include <deque> #include <iostream>   enum TokenType {     BAD_TOKEN,     NUM_TOKEN,     ADD_TOKEN,     SUB_TOKEN,     MUL_TOKEN,     DIV_TOKEN,     LPAREN_TOKEN,     RPAREN_TOKEN,     ENDFILE_TOKEN };   class Token { private:     TokenType type_;     std::string valueStr_; public:     Token() : type_(BAD_TOKEN) {}     Token(TokenType t,std::string s) :         type_(t),valueStr_(s) {}       bool operator ==(const Token& t) {         if (type_ == t.type_ &&             valueStr_ == t.valueStr_) {             return true;         }         return false;     }     Token(const Token& t) {         if (*this != t) {             type_ = t.type_;             valueStr_ = t.valueStr_;         }     }       bool operator != (const Token& t) {         return !(*this == t);     }       Token& operator=(const Token& t) {         if (*this != t) {             type_ = t.type_;             valueStr_ = t.valueStr_;         }         return *this;     }     /*void SetType(TokenType type) { type_ = type; }     void SetValue(double value) { value_ = value; }     void SetValStr(std::string valueStr) { valueStr_ = valueStr; }*/     TokenType GetType() { return type_; }     std::string GetValStr() { return valueStr_; } };     class Expression2Tokens {           std::string contentStr_;     Expression2Tokens& operator=(const Expression2Tokens&) {};     Expression2Tokens(const Expression2Tokens&);     enum Status {         INIT_STATUS,         NUM_STATUS,         OPERATOR_STATUS,         LPAREN_STATUS,         RPAREN_STATUS,         END_STATUS,         ERROR_STATUS     }; public:     std::deque<Token> tokenDeque_;     Expression2Tokens(std::string s):contentStr_(s){}     bool Analyzer();     void PrintTokens() {         for (std::deque<Token>::iterator it = tokenDeque_.begin();             it != tokenDeque_.end(); it++) {             std::cout << "type: " << (*it).GetType() << ", string: " << (*it).GetValStr() << std::endl;         }         std::cout << std::endl;     }   };   class ParseExpression {     Expression2Tokens   express2token_;     ParseExpression& operator=(const ParseExpression&) {};     ParseExpression(const ParseExpression&);     double result_;     double ParseTerm();     double ParsePrimaryExpression(); public:     ParseExpression(std::string s) :         express2token_(s), result_(0.0){}     bool StartParse();     double GetResult() { return result_; }   };

　　

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#include "token.h" #include <iostream>   bool Expression2Tokens::Analyzer() {     bool bRet = false;     size_t index = 0, valueBeg = 0, valueEnd = 0;     Status status = INIT_STATUS;     for (;index < contentStr_.size();index++)     {         if (isdigit(contentStr_[index])) {             if (status != NUM_STATUS) {                 status = NUM_STATUS;                 valueBeg = index;             }             continue;         }         //对于 非数字进行判断         if (NUM_STATUS == status ) {             std::string s(contentStr_.substr(valueBeg, index - valueBeg));             Token t(NUM_TOKEN,s);             tokenDeque_.push_back(t);             valueBeg = 0;         }           if (contentStr_[index] == '+') {             Token t(ADD_TOKEN, "+");             tokenDeque_.push_back(t);             status = OPERATOR_STATUS;             continue;         }else if (contentStr_[index] == '-') {             Token t(SUB_TOKEN, "-");             tokenDeque_.push_back(t);             status = OPERATOR_STATUS;             continue;         }else if (contentStr_[index] == '*') {             Token t(MUL_TOKEN, "*");             tokenDeque_.push_back(t);             status = OPERATOR_STATUS;             continue;         }else if (contentStr_[index] == '/') {             Token t(DIV_TOKEN,"/");             tokenDeque_.push_back(t);             status = OPERATOR_STATUS;             continue;         }else if (contentStr_[index] == ';')         {             Token t(ENDFILE_TOKEN, ";");             tokenDeque_.push_back(t);             status = END_STATUS;             bRet = true;             return bRet;         }                   else {             std::cerr << "analyzer error (" << contentStr_[index] << ")" <<  std::endl;             status = ERROR_STATUS;             return false;         }     }       return bRet; }   double ParseExpression::ParsePrimaryExpression() {     Token token;     token = express2token_.tokenDeque_.front();     if (token.GetType() == NUM_TOKEN) {         //return  atof(token.GetValStr().c_str());         express2token_.tokenDeque_.pop_front();         return stod(token.GetValStr());     }     std::cerr << "syntax error." << std::endl;     exit(1);     return 0.0; }         double ParseExpression::ParseTerm() {     double dRet;     double v;       Token token;       dRet = ParsePrimaryExpression();     for (;;) {         token = express2token_.tokenDeque_.front();         if (token.GetType() != MUL_TOKEN             && token.GetType() != DIV_TOKEN) {             break;         }         express2token_.tokenDeque_.pop_front();         v = ParsePrimaryExpression();         if (token.GetType() == MUL_TOKEN) {             dRet *= v;         }         else if (token.GetType() == DIV_TOKEN) {             dRet /= v;         }     }       return dRet; }     bool ParseExpression::StartParse() {     bool bRet = false;     if (!express2token_.Analyzer())         return bRet;     express2token_.PrintTokens();             double v;     Token token;       result_ = ParseTerm();     for (;;) {         token = express2token_.tokenDeque_.front();         if (token.GetType() != ADD_TOKEN &&             token.GetType() != SUB_TOKEN) {             break;         }         express2token_.tokenDeque_.pop_front();         v = ParseTerm();         if (token.GetType() == ADD_TOKEN) {             result_ += v;         }         else if (token.GetType() == SUB_TOKEN) {             result_ -= v;         }     }       bRet = true;     return bRet;   }

　　测试代码如下：

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// MyParse.cpp : 定义控制台应用程序的入口点。 //   #include "stdafx.h" #include "token.h" #include <iostream>   int main() {           Expression2Tokens e("1+2/3*45-67-89+999;");     if (e.Analyzer()) {         e.PrintTokens();     }       ParseExpression p("132+243/7*4455-6-89+34;");     if(p.StartParse())         std::cout << "result: " << p.GetResult() << std::endl;     return 0; }

　　

type: 1, string: 1
type: 2, string: +
type: 1, string: 2
type: 5, string: /
type: 1, string: 3
type: 4, string: *
type: 1, string: 45
type: 3, string: -
type: 1, string: 67
type: 3, string: -
type: 1, string: 89
type: 2, string: +
type: 1, string: 999
type: 8, string: ;

type: 1, string: 132
type: 2, string: +
type: 1, string: 243
type: 5, string: /
type: 1, string: 7
type: 4, string: *
type: 1, string: 4455
type: 3, string: -
type: 1, string: 6
type: 3, string: -
type: 1, string: 89
type: 2, string: +
type: 1, string: 34
type: 8, string: ;

result: 154723
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