//调试环境 vs2015
//本人菜鸟一枚,不喜勿喷! 谢谢!!!
//主要思想引自 https://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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