题解 | #简单计算器#

#include <iostream>
#include<stack>
#include<string>
#include<map>
using namespace std;

int main() {
    string str;
    string str_s;
    int tag = 0;
    stack<double> Mystack;
    stack<char> Stack_1;
    map<char, int> Map;
    Map['+'] = 1;
    Map['-'] = 1;
    Map['*'] = 2;
    Map['/'] = 2;
    while (getline(cin, str)) {
        if (str == "0") {
            break;
        }
        str.insert(0, " ");
        str.push_back(' ');
        for (int i = 1; i < str.size(); ++i) {
            if (str[i] == ' ' && str[i - 1] >= '0' && str[i - 1] <= '9') {
                double x = stod(str.substr(tag, i - tag + 1));
                Mystack.push(x);
            }
            else if (str[i] >= '0' && str[i] <= '9' && str[i - 1] == ' ') {
                tag = i;
            }
            if (str[i] == '+' || str[i] == '-' || str[i] == '*' || str[i] == '/') {
                if (Stack_1.empty()) {
                    Stack_1.push(str[i]);
                }
                else {

                    if (Map[Stack_1.top()] >= Map[str[i]]) {
                        while (Stack_1.empty() == false && Map[Stack_1.top()] >= Map[str[i]]) {
                            double x1 = Mystack.top();
                            Mystack.pop();
                            double x2 = Mystack.top();
                            Mystack.pop();
                            if (Stack_1.top() == '+') {
                                Mystack.push(x1 + x2);
                            }
                            else if (Stack_1.top() == '-') {
                                Mystack.push(x2 - x1);
                            }
                            else if (Stack_1.top() == '*') {
                                Mystack.push(x2 * x1);
                            }
                            else if (Stack_1.top() == '/') {
                                Mystack.push((double)x2 / x1);
                            }
                            Stack_1.pop();
                        }
                        Stack_1.push(str[i]);
                    }
                    else {
                        Stack_1.push(str[i]);
                    }
                }
            }
        }
        while (!Stack_1.empty()) {
            double x1 = Mystack.top();
            Mystack.pop();
            double x2 = Mystack.top();
            Mystack.pop();
            if (Stack_1.top() == '+') {
                Mystack.push(x1 + x2);
            }
            else if (Stack_1.top() == '-') {
                Mystack.push(x2 - x1);
            }
            else if (Stack_1.top() == '*') {
                Mystack.push(x2 * x1);
            }
            else if (Stack_1.top() == '/') {
                Mystack.push((double)x2 / x1);
            }
            Stack_1.pop();
        }
        printf("%.2lf\n", Mystack.top());
        Mystack.pop();

    }
}
// 64 位输出请用 printf("%lld")