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C++ primer 练习9.52 适配器stack 中缀表达式

2019年02月25日  | 移动技术网IT编程  | 我要评论

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//调试环境 vs2015
//本人菜鸟一枚，不喜勿喷！ 谢谢！！！
//主要思想引自  http://www.cnblogs.com/dolphin0520/p/3708602.html
//主要代码引自  https://blog.csdn.net/fengzhanghao23/article/details/47380793
//改动：1.可支持负数运算，但采用的是字符串string的find搜索操作和substr拷贝操作
//           2.循环操作采用c++11标准的范围for语句实现
//           3.输入采用文件输入，其文件名，存储地址及数据可自行修改

#include "stdafx.h"
#include<iostream>
#include<fstream>
#include<vector>
#include<string>
#include<stack>
using namespace std;
int priority(string opt)
{
 int p = 0;
 if (opt == "(")
  p = 1;
 if (opt == "+" || opt == "-")
  p = 2;
 if (opt == "*" || opt == "/")
  p = 3;
 return p;
}
void calculate(stack<double> &opdstack, string opt)
{
 double ropd = 0;
 double lopd = 0;
 double result = 0;
 if (opt == "+")
 {
  ropd = opdstack.top();
  opdstack.pop();
  lopd = opdstack.top();
  opdstack.pop();
  result = lopd + ropd;
  opdstack.push(result);
 }
 if (opt == "-")
 {
  ropd = opdstack.top();
  opdstack.pop();
  lopd = opdstack.top();
  opdstack.pop();
  result = lopd - ropd;
  opdstack.push(result);
 }
 if (opt == "*")
 {
  ropd = opdstack.top();
  opdstack.pop();
  lopd = opdstack.top();
  opdstack.pop();
  result = lopd * ropd;
  opdstack.push(result);
 }
 if (opt == "/")
 {
  ropd = opdstack.top();
  opdstack.pop();
  lopd = opdstack.top();
  opdstack.pop();
  result = lopd / ropd;
  opdstack.push(result);
 }
}
double calexpression(vector<string> sv)
{
 stack<double> stack_opd;
 stack<string> stack_opt;
 for (auto c : sv)
 {
  if (c == "+" || c == "-" || c == "*" || c == "/")
  {
   if (stack_opt.size() == 0)
    stack_opt.push(c);
   else
   {
    int c_p = priority(c);
    string top_opt = stack_opt.top();
    int opt_p = priority(top_opt);
    if (c_p > opt_p)
     stack_opt.push(c);
    else
    {
     while (c_p <= opt_p)
     {
      calculate(stack_opd, top_opt);
      stack_opt.pop();
      if (stack_opt.size() > 0)
      {
       top_opt = stack_opt.top();
       opt_p = priority(top_opt);
      }
      else
       break;
     }
     stack_opt.push(c);
    }
   }
  }
  else if (c == "(")
   stack_opt.push(c);
  else if (c == ")")
  {
   while (stack_opt.top() != "(")
   {
    string top_opt = stack_opt.top();
    calculate(stack_opd, top_opt);
    stack_opt.pop();
   }
   stack_opt.pop();
  }
  else
  {
   if (c.find('-') == 0)
    stack_opd.push(-stod(c.substr(c.find('-') + 1)));
   else
    stack_opd.push(stod(c));
  }
 }
 while (stack_opt.size() != 0)
 {
  string top_opt = stack_opt.top();
  calculate(stack_opd, top_opt);
  stack_opt.pop();
 }
 return stack_opd.top();
}
int main()
{
 cout << "------this is a function test of test_9_52------" << endl;
 cout << "caution!!! the data stored in file of test_9_52.txt" << endl;
 ifstream ifs("test_9_52.txt");
 string s;
 vector<string> sv;
 if (ifs)
 {
  while (ifs >> s)
   sv.push_back(s);
 }
 else
  cout << "the file is not open!!!" << endl;
 cout << "the expression: ";
 for (auto c : sv)
  cout << c << " ";
 cout << endl;
 cout << "it's calculation results is: " << calexpression(sv) << endl;
 cout << endl;
 return 0;
}

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