C++ 向量赋值

Question

我的程序应该将输入读取为长度为整数的输入，后跟（足够）带括号的浮点数和简单运算符，并输出表达式的值。例如，如果输入是 11 1 + 2 ^ 3 / 4 * 5 - 6，结果应该等于 (1 + (((2 ^ 3) / 4) * 5)) - 6，或 5。但是，即使我输入 5 1 + 2 + 3，输出也是 5 而不是 6。我认为这可能是因为有很多矢量分配，特别是标记线（我在调试时发现的）。

我的代码（抱歉，如果它不能自我解释）：

#include <iostream>
#include <string>
#include <vector>
#include <cmath>
using namespace std;

float op(char op, float x, float y)
{
    switch (op)
    {
        case '+':
        {
            return x+y;
            break;
        }
        case '-':
        {
            return x-y;
            break;
        }
        case '*':
        {
            return x*y;
            break;
        }
        case '/':
        {
            return x/y;
            break;
        }
        case '^':
        {
            return pow(x,y);
            break;
        }
        default:
        {
            cout << "Error: bad input ";
            return 0;
        }
    }
}

float nopars(vector<string> stack, int stackl, vector<char> ops, int opsr)
{
    int len = stackl, opsrr = opsr;
    vector<string> nstack, nnstack;
    vector<char> nops = ops, nnops;
    nstack = stack;
    while (opsrr != 0)
    {
        string s1 (1, nops[0]);
        for (int i = 0; i < len; i++)
        {
            if (nstack[i] == s1)
            {
                for (int j = 0; j < len - 2; j++)
                {
                    nnstack = {};
                    if (j == i-1)
                    {
                        nnstack.push_back(to_string(op(nops[0], stof(nstack[i-1]), stof(nstack[i+1]))));
                    }
                    else if (j < i-1)
                    {
                        nnstack.push_back(nstack[j]);
                    }
                    else if (j > i-1)
                    {
                        nnstack.push_back(nstack[j+2]);
                    }
                }
                len = len - 2;
                nstack = nnstack;                                   //I think this is wrong? 
                i--;
            }
        }
        nnops = {};
        for (int i = 0; i < opsr-1; i++)
        {
            nnops.push_back(nops[i+1]);
        }
        opsrr--;
        nops = nnops;
    }
    return stof(nstack[0]);
}

float all(vector<string> stack, int stackl, vector<char> ops, int opsr)
{
    int t1 = 0, t2 = 0;
    int len = stackl;
    int nprs;
    vector<string> nstack, nnstack, nstck;
    nstack = stack;
    while (true)
    {
        nprs = 0;
        for (int i = 0; i < len; i++)
        {
            if (nstack[i] == "(")
            {
                nprs = 1;
                t1 = i;
            }
            else if (nstack[i] == ")")
            {
                nprs = 1;
                t2 = i;
                nstck = {};
                for (int j = t1 + 1; j < t2; j++)
                {
                    nstck.push_back(nstack[j]);
                }
                for (int j = 0; j < len - t2 + t1; j++)
                {
                    if (j == t1)
                    {
                        nnstack.push_back(to_string(nopars(nstck, t2-t1-1, ops, opsr)));
                    }
                    else if (j < t1)
                    {
                        nnstack.push_back(nstack[j]);
                    }
                    else if (j > t1)
                    {
                        nnstack.push_back(nstack[j+t2-t1]);
                    }
                }
                len = len - t2 + t1;
                break;
            }
        }
        if (nprs == 0)
        {
            break;
        }
        nstack = nnstack;
    }
    return nopars(nstack, len, ops, opsr);
}

void calculate()
{
    vector<string> stack;
    int stackl;
    string t;
    cin >> stackl;
    for (int i = 0; i < stackl; i++)
    {
        cin >> t;
        stack.push_back(t);
    }
    cout << all(stack, stackl, {'^', '/', '*', '-', '+'}, 5);
}

int main()
{
    calculate();
    return 0;
}

Answer 1

似乎错误出在无意重复的声明中nnstack = {}。

#include <iostream>
#include <string>
#include <vector>
#include <cmath>
using namespace std;

float op(char op, float x, float y)
{
    switch (op)
    {
        case '+':
        {
            return x+y;
            break;
        }
        case '-':
        {
            return x-y;
            break;
        }
        case '*':
        {
            return x*y;
            break;
        }
        case '/':
        {
            return x/y;
            break;
        }
        case '^':
        {
            return pow(x,y);
            break;
        }
        default:
        {
            cout << "Error: bad input ";
            return 0;
        }
    }
}

float nopars(vector<string> stack, int stackl, vector<char> ops, int opsr)
{
    int len = stackl, opsrr = opsr;
    vector<string> nstack, nnstack;
    vector<char> nops = ops, nnops;
    nstack = stack;
    while (opsrr != 0)
    {
        string s1 (1, nops[0]);
        for (int i = 0; i < len; i++)
        {
            if (nstack[i] == s1)
            {
                nnstack = {};                              //this was missing
                for (int j = 0; j < len - 2; j++)
                {
                    //nnstack = {};                        //this was misplaced
                    if (j == i-1)
                    {
                        nnstack.push_back(to_string(op(nops[0], stof(nstack[i-1]), stof(nstack[i+1]))));
                    }
                    else if (j < i-1)
                    {
                        nnstack.push_back(nstack[j]);
                    }
                    else if (j > i-1)
                    {
                        nnstack.push_back(nstack[j+2]);
                    }
                }
                len = len - 2;
                nstack = nnstack;
                i--;
            }
        }
        nnops = {};
        for (int i = 0; i < opsr-1; i++)
        {
            nnops.push_back(nops[i+1]);
        }
        opsrr--;
        nops = nnops;
    }
    return stof(nstack[0]);
}

float all(vector<string> stack, int stackl, vector<char> ops, int opsr)
{
    int t1 = 0, t2 = 0;
    int len = stackl;
    int nprs;
    vector<string> nstack, nnstack, nstck;
    nstack = stack;
    while (true)
    {
        nprs = 0;
        for (int i = 0; i < len; i++)
        {
            if (nstack[i] == "(")
            {
                nprs = 1;
                t1 = i;
            }
            else if (nstack[i] == ")")
            {
                nprs = 1;
                t2 = i;
                nstck = {};
                for (int j = t1 + 1; j < t2; j++)
                {
                    nstck.push_back(nstack[j]);
                }
                for (int j = 0; j < len - t2 + t1; j++)
                {
                    if (j == t1)
                    {
                        nnstack.push_back(to_string(nopars(nstck, t2-t1-1, ops, opsr)));
                    }
                    else if (j < t1)
                    {
                        nnstack.push_back(nstack[j]);
                    }
                    else if (j > t1)
                    {
                        nnstack.push_back(nstack[j+t2-t1]);
                    }
                }
                len = len - t2 + t1;
                break;
            }
        }
        if (nprs == 0)
        {
            break;
        }
        nstack = nnstack;
    }
    return nopars(nstack, len, ops, opsr);
}

void calculate()
{
    vector<string> stack;
    int stackl;
    string t;
    cin >> stackl;
    for (int i = 0; i < stackl; i++)
    {
        cin >> t;
        stack.push_back(t);
    }
    cout << all(stack, stackl, {'^', '/', '*', '-', '+'}, 5);
}

int main()
{
    calculate();
    return 0;
}

Answer 2

二进制循环 LL 解析器

#include <iostream>
#include <string>
#include <sstream>
#include <functional>
#include <iterator>
#include <cmath>
#include <map>

using namespace std;
using T = float;

map< int, map<std::string, std::function<T(const T&, const T&)> > > m_foo = 
    { {1, { { "+", std::plus<T>() }, { "-", std::minus<T>() }  } },
      {2, { { "*", std::multiplies<T>() }, { "/", std::divides<T>() } } },
      {3, { { "^", powf } } } };

T calc_ll(istream_iterator<string>& t, int level) {
   if ( !m_foo.contains(level) ) return  std::stof(*t++);

   auto result = calc_ll(t, level+1);
   auto l = m_foo[level];
   while ( l.find(*t) != l.end() ) {
      auto foo = l.find(*t)->second; 
      result = foo(result, calc_ll(++t, level+1) );
   }
   return result;
}

int main()
{
    std::stringstream ss(std::string("1 + 2 ^ 3 / 4 * 5 - 6"));
    auto t = istream_iterator<string>(ss);
    cout << "result : " << calc_ll( t, 1 );
    return 0;
}

link https://godbolt.org/z/9vPMGn

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