简单计算器

支持括号,浮点运算,需要输入一串 运算表达式 后面加一个#

#include<bits/stdc++.h>
using namespace std;
char pre[7][7]=
{
    '>','>','<','<','<','>','>',
    '>','>','<','<','<','>','>',
    '>','>','>','>','<','>','>',
    '>','>','>','>','<','>','>',
    '<','<','<','<','<','=','<',
    '>','>','>','>','>','>','>',
    '<','<','<','<','<','<','=',
};
stack<double>oprn;
stack<char>optr;
bool isOprn(char ch)
{
    if(ch>='0'&&ch<='9'||ch=='.')
        return true;
    return false;
}
double compute(double a,double b,char c)
{
    switch(c)
    {
    case '+':
        return a+b;
        break;
    case '-':
        return a-b;
        break;
    case '*':
        return a*b;
        break;
    case '/':
        return a/b;
        break;
    }
}
int getIndex(char c)
{
    switch(c)
    {
    case '+':
        return 0;
        break;
    case '-':
        return 1;
        break;
    case '*':
        return 2;
        break;
    case '/':
        return 3;
        break;
    case '(':
        return 4;
        break;
    case ')':
        return 5;
        break;
    case '#':
        return 6;
        break;
    }
}
double calculate(string str)
{
    while(!oprn.empty())oprn.pop();
    while(!optr.empty())optr.pop();
    optr.push('#');
    int flag=0,lefti,righti,i=0,opli,opri;;

    double opnl,opnr;
    while(!optr.empty())
    {
        if(flag==0&&(isOprn(str[i])||(i==0||str[i-1]=='(')&&str[i]=='-'&&isOprn(str[i+1])))
        {
            lefti=i;
            flag=1;
        }
        else if(!isOprn(str[i]))
        {
            if(flag==1)
            {
                righti=i;
                stringstream num(str.substr(lefti,righti-lefti));
                num>>opnl;
                oprn.push(opnl);
                flag=0;
            }
            opri=getIndex(str[i]);
            opli=getIndex(optr.top());
            while(1)
            {
                if(pre[opli][opri]=='<')
                {
                    optr.push(str[i]);
                    break;
                }
                else if(pre[opli][opri]=='>')
                {
                    char op=optr.top();
                    optr.pop();
                    opnr=oprn.top();
                    oprn.pop();
                    opnl=oprn.top();
                    oprn.pop();
                    oprn.push(compute(opnl,opnr,op));
                    opli=getIndex(optr.top());
                }
                else if(pre[opli][opri]=='=')
                {
                    optr.pop();
                    break;
                }
            }
        }
        i++;
    }
    double ans=oprn.top();
    oprn.pop();
    return ans;
}
int main()
{
    int t;
    cin>>t;
    while(t--)
    {
        string str;
        cin>>str;
        cout<<setprecision(4)<<fixed<<calculate(str)<<endl;
    }
    return 0;
}