题解 | 简单计算器

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <stack>
#include <string>
using namespace std;

int prio(char c) {
    int p;
    if (c == '+')p= 1;
    else if (c == '-')p= 1;
    else if (c == '*')p= 2;
    else if (c == '/')p= 2;
    return p;
}

float com(float f1, float f2, char c) {
    float ans;
    if (c == '+')ans = f1+f2;
    else if (c == '-')ans= f1 - f2;
    else if (c == '*')ans= f1 * f2;
    else if (c == '/')ans= f1 / f2;
    return ans;
}

int main() {
    string s;
    while (getline(cin, s)) {
        if (s == "0")break;
        stack<char>sign;
        stack<float>num;
        int n = 0;
  //      cout<<"s = "<<s<<endl;
        for (int i = 0; i < s.size(); i++) {
            if (s[i] == '+' || s[i] == '-' || s[i] == '*' || s[i] == '/') {
                if (sign.empty())sign.push(s[i]);
                else {
                     while(!sign.empty()&&prio(sign.top()) >= prio(s[i])) {
                        char c = sign.top();
                  //      sign.push(s[i]);
                        float n1 = num.top();
                        num.pop();
                        float n2 = num.top();
                        num.pop();
                        float ans = com(n2, n1, c);
                        num.push(ans);
                        sign.pop();
                    }
                    sign.push(s[i]);
                }
            } 
            else if (s[i] >= '0' && s[i] <= '9') {
                n = n * 10 + (s[i] - '0');
            } else {
     //           cout<<"n = "<<n<<endl;
                if(s[i-1]>= '0' && s[i-1] <= '9')num.push(n);
                n = 0;
            }
        }
        num.push(n);
  //      cout<<n<<endl;
        while (!sign.empty()) {
            char c = sign.top();
            sign.pop();
            float n1 = num.top();
            num.pop();
            float n2 = num.top();
            num.pop();
            float ans = com(n2, n1, c);
            num.push(ans);
        }
        printf("%.2f\n",num.top());
    }
}
// 64 位输出请用 printf("%lld")