题解 | 简单计算器

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

int main() {
    string s;
    map<char, int> rank = {{'+', 1}, {'-', 1}, {'*', 2}, {'/', 2}, {'.', 0}};
    while (getline(cin, s)) {
        if (s == "0") break;
        s.push_back('.');
        stack<char>op;
        stack<float> num;
        string r;
        for (int i = 0; i < s.size(); ++i) {
            if (s[i] <= '9' && s[i] >= '0') r.push_back(s[i]);
            else if (s[i] != ' ') {
                float temp = stof(r);
                num.push(temp);
                r.clear();
                while (!op.empty() && rank[op.top()] >= rank[s[i]]) {
                    float rhs = num.top();
                    num.pop();
                    float  lhs = num.top();
                    num.pop();
                    char c = op.top();
                    op.pop();
                    if (c == '+') num.push(lhs + rhs);
                    else if (c == '-') num.push(lhs - rhs);
                    else if (c == '*') num.push(lhs * rhs);
                    else if (c == '/') num.push(lhs / rhs);
                }
                if (s[i] == '.') cout << setiosflags(ios::fixed) << setprecision(
                                              2) << num.top() << endl;
                else op.push(s[i]);
            }
        }
    }
    return 0;
}