[C/C++基礎]- 利用標準C++工具開發簡易數學直譯器

[C/C++基礎]- 利用標準C++工具開發簡易數學直譯器 

本篇要分享利用標準C++工具開發簡易數學直譯器，有興趣的(C/P)同好，歡迎來(C/P)一下哈哈 ^ ^ 。

程式碼

#include <cstdlib> #include <iostream> #include <string>   // string #include <sstream>  // stringstream #include <stack>    // stack #include <vector>   // vector #include <cctype>   // isdigit() usingnamespace std; // define const variable for readability constint OPERATOR = 0; constint OPERAND  = 1;   class Expression { // constructor public:   Expression();   Expression(constchar*);   // public member function public:   double eval(); // get eval result   // private data member private:   stack<double> operandStack; // stack to store operand   stack<char> operatorStack;  // stack to store operator   string infix;               // string to hold infix expression   vector<pair<int, string> > suffix; // vector to hold suffix expression   // private member function private:   string char2str(constchar &);      // convert char to string   string dbl2str(constdouble &);     // convert double to string   double str2dbl(const string &);     // convert string to double   bool isoperator(constchar &);      // identify whether it is an operator   void parseOperand(constdouble &);  // parse operand to operandStack   void parseOperator(constchar &);   // parse operator to operatorStack   int operatorPriority(constchar&); // define operator priority   void toSuffix(void);        // convert infix to suffix   double calculate(const string &, constdouble &, constdouble &); // calculate result by operator and operand };   // constructor Expression::Expression() {   }   // constructor Expression::Expression(constchar *val) {   this->infix = string(val); // fill infix by constructor   this->toSuffix();          // convert infix to suffix }   // convert char to string string Expression::char2str(constchar &c) {   stringstream ss;   ss << c;     return ss.str(); }   // convert double to string string Expression::dbl2str(constdouble &d) {   stringstream ss;   ss << d;     return ss.str(); }   // convert string to double double Expression::str2dbl(const string &s) {   stringstream ss(s);   double d;   ss >> d;     return d; }   // identify whether it is an operator bool Expression::isoperator(constchar &c) {   switch(c) {     case '(' :     case ')' :     case '+' :     case '-' :     case '*' :     case '/' : returntrue;     default  : returnfalse;   } }   // parse operand to operandStack void Expression::parseOperand(constdouble &dOperand) {   suffix.push_back(make_pair(OPERAND, dbl2str(dOperand))); }   // parse operator to operatorStack void Expression::parseOperator(constchar &cOperator) {   if (operatorStack.empty() || cOperator == '(') {     operatorStack.push(cOperator);   }   else {     if (cOperator == ')') {       while(operatorStack.top() != '(') {         suffix.push_back(make_pair(OPERATOR, char2str(operatorStack.top())));         operatorStack.pop();           if (operandStack.empty()) break;       }       // Remove '('       operatorStack.pop();     }     else { // not ')'       while(operatorPriority(cOperator) <= operatorPriority(operatorStack.top()) && !operatorStack.empty()) {         suffix.push_back(make_pair(OPERATOR, char2str(operatorStack.top())));         operatorStack.pop();           if (operatorStack.empty())           break;       }       operatorStack.push(cOperator);     }   } }   // define operator priority int Expression::operatorPriority(constchar &cOperator) {   switch(cOperator) {     case '*' :     case '/' : return 3;     case '+' :     case '-' : return 2;     case '(' : return 1;     default  : return 0;   } }   // Convert infix to suffix // Algorithm : Parse infix string one char by one char. If char //             is operator, check if _operand is "", if not, let //             _operand to operandStack, and make _operand string //             clear, then let operator to operatorStack. If char //             is digit, concatenate to _operand string. void Expression::toSuffix(void) {   string _operand;   for(string::iterator p = infix.begin(); p != infix.end(); ++p) {     if (isoperator(*p)) {       if (_operand != "") {         parseOperand(str2dbl(_operand));         _operand.clear();       }       parseOperator(*p);     } elseif (isdigit(*p))       _operand.push_back(*p);   }     // If _operand is not "", let _operand to operandStack.   if (_operand != "")     parseOperand(str2dbl(_operand));     // If operatorStack is not empty, push it to suffix vector until   // operatorStack is empty.   while(!operatorStack.empty()) {     suffix.push_back(make_pair(OPERATOR,char2str(operatorStack.top())));     operatorStack.pop();   } }   // calculate result by operator and operand double Expression::calculate(const string &op, constdouble &operand1, constdouble &operand2) {   if (op == "+")     return operand2 + operand1;   elseif (op == "-")     return operand2 - operand1;   elseif (op == "*")     return operand2 * operand1;   elseif (op == "/")     return operand2 / operand1;   else     return 0; }   // get eval result double Expression::eval(void) {   // Clear OperandStack   while(!operandStack.empty())     operandStack.pop();     for(vector<pair<int, string> >::iterator iter = suffix.begin(); iter != suffix.end(); ++iter) {     if (iter->first == OPERATOR) {       double operand1 = operandStack.top();       operandStack.pop();       double operand2 = operandStack.top();       operandStack.pop();       operandStack.push(calculate(iter->second, operand1, operand2));     }     elseif (iter->first == OPERAND) {       operandStack.push(str2dbl(iter->second));     }   }     return operandStack.top(); } int main(int argc, char *argv[]) {     Expression x1("10+20*5");     cout << "x1=" << x1.eval() << endl;       Expression x2("5*20+10+1+2-3+99");     cout << "x2=" << x2.eval() << endl;     system("PAUSE");     return EXIT_SUCCESS; }