公式字符串求值

#include <iostream>
#include <string>
#include <vector>
#include <deque>
#include <sstream>
using namespace std;

void addNum(deque<string>& deq, int num)
{
    if(!deq.empty())
    {
        int cur = 0;
        string top = deq.back();
        deq.pop_back();
        if(top == "+" || top == "-")
        {
             deq.push_back(top);
        }
        else
        {
            cur = stoi(deq.back());
            deq.pop_back();
            num = top == "*" ? (cur * num) : (cur / num);

        }
    }
    deq.push_back(to_string(num));
}

int getNum(deque<string> &deq)
{
    int res = 0;
    bool add = true;
    string cur;
    int num;
    while(!deq.empty())
    {
        cur = deq.front();
        deq.pop_front();
        if(cur == "+")
            add = true;
        else if(cur == "-")
            add = false;
        else
        {
            num = stoi(cur);
            res += add ? num : (-num);
        }
    }
    return res;
}

vector<int> value(string str, int i)
{
    deque<string> deq;
    int pre = 0;
    vector<int> bra(2);
    while(i < str.size() && str[i] != ')')
    {
        if(str[i] >= '0' && str[i] <= '9')
            pre = pre * 10 + str[i++] - '0';
        else if(str[i] != '(')
                {
                    addNum(deq, pre);
                    stringstream stream;
                    stream << str[i++];
                    string temp = stream.str();
                    deq.push_back(temp);
                    pre = 0;
                }
        else
        {
            bra = value(str, i + 1);
            pre = bra[0];
            i = bra[1] + 1;
        }
    }
    addNum(deq, pre);
    bra[0] = getNum(deq);
    bra[1] = i;
    return bra;
}
int main()
{
    string str = "48*((70-65)-43)+8*1";
    string str1 = "3+1*4";
    cout << value(str, 0)[0] << endl;
}