数据结构与算法分析 c++11 练习3.22 中缀表达式转后缀表达式，后缀表达式计算， 多项式计算

 练习3.22 中缀表达式转后缀表达式，后缀表达式计算， 多项式计算

polynome.h

#pragma once#include <string>#include <stack>  #include <cctype>//判断字符类型需要的头文件#include <vector>#include <sstream>#include <cstdlib>class Polynome {public:Polynome() = default;Polynome(std::string str) :infix(str) { }std::string infixToPostfix();float getResultUsePostfix();~Polynome() {}protected:void processOperator(std::string &s, char opera );void CalculateResult(const char *oper, std::stack<double>& tmpStack);bool isPriorityLow(char currOper, char topOper);bool isNumber(char s);void split(const std::string& strOrignal, const char ch, std::vector<std::string>& vctString);private:std::stack<char> operators;std::string infix;std::string postfix;};

polynome.cpp

#include "polynome.h"using namespace std;string Polynome::infixToPostfix(){for (size_t i = 0; i < infix.length(); i++) {if (isNumber(infix[i])) {           postfix += infix[i];}else {postfix += ' ';processOperator(postfix, infix[i]);  }}if (postfix.length() > 0) {while (operators.size() > 0) {postfix += ' ';postfix += operators.top();operators.pop();}return postfix;}else {return "";}}float Polynome::getResultUsePostfix(){if (postfix.length() <= 0) {return 0;}stack<double> tmpStack;double dbl;vector <string> temVec;split(postfix, ' ', temVec);for (size_t i = 0; i < temVec.size(); i++) {if(temVec[i]=="+"|| temVec[i] == "-"|| temVec[i] == "*"|| temVec[i]== "/"){CalculateResult(temVec[i].c_str(), tmpStack);}else {dbl = atof(temVec[i].c_str());tmpStack.push(dbl);}}return tmpStack.top();}void Polynome::processOperator(string & s, char opera){switch (opera) {case '+':case '-':case '*':case '/':if (operators.size() <= 0) {operators.push(opera);}else if (isPriorityLow(opera, operators.top())) {while (operators.size() > 0 && isPriorityLow(opera, operators.top())) {s += operators.top();s += ' ';operators.pop();}operators.push(opera);}else {operators.push(opera);}break;case('('):operators.push(opera);break;case(')')://将栈中元素弹出加到后缀表达式尾,直到遇到运算符"("while (operators.top() != '(') {s += operators.top();operators.pop();}operators.pop();break;}}void Polynome::CalculateResult(const char* oper, stack<double>& tmpStack){if (tmpStack.size() < 2) {return;}//栈是先进后出,所以先弹出的是第二个值double secondVal = tmpStack.top();tmpStack.pop();double firstVal = tmpStack.top();tmpStack.pop();double result = 0;switch (*oper) {case '+':result = firstVal + secondVal;break;case '-':result = firstVal - secondVal;break;case '*':result = firstVal * secondVal;break;case '/':result = firstVal / secondVal;break;default:break;}tmpStack.push(result);}/*** 判断当前运算符与栈顶运算符的优先级大小*/bool Polynome::isPriorityLow(char currOper, char topOper){if (currOper == '+' || currOper == '-') {if (topOper == '*' || topOper == '/' || topOper == '+' || topOper == '-') {return true;}}if (currOper == '*' || currOper == '/') {if (topOper == '*' || topOper == '/') {return true;}}return false;}bool Polynome::isNumber(char s){string opers = "+-*/()^";for (int i = 0; i < opers.length(); i++) {if (s == opers.at(i)) {return false;}}return true;}void Polynome::split(const string & strOrignal,const char ch, std::vector<string>& vctString){istringstream iss(strOrignal);string item;while (getline(iss, item, ch)) vctString.push_back(item);stringstream stream;stream << ch;           auto it = vctString.begin();while (it != vctString.end()){if (*it ==stream.str()|| *it =="")               //将char 转化为stringit = vctString.erase(it);elseit++;}return;}

main.cpp

#include <iostream>  #include <stdio.h>  #include <stdlib.h>  #include "polynome.h"using namespace std;int main(){string infix = {"4.99*1.06+5.99+6.99*1.06"};string infix1 = { "a+b*c+(d*e+f)*g" };cout << "请输入多项式(不要空格)：" << endl;while(1){string infix3;string postfix;cin >> infix3;Polynome inf(infix3);postfix = inf.infixToPostfix();cout <<"后缀表达式为："<< postfix << endl;float result = inf.getResultUsePostfix();cout << "计算结果为: " << result << endl;}return 0;}