STL容器是必要的

直接上题解好吧！

#include <bits/stdc++.h>
using namespace std;
int main() {
    string s;
    cin >> s;
    if(s.size() == 1 && s[0] == '@') cout << 0;
    stack<int> stk;
    string n;
    for(int i = 0;i < s.size();i++){
        if(s[i] == '@') break;
        if(s[i] == '.'){
            int num = 0,w = 1;
            reverse(n.begin(),n.end());
            for(int i = 0;i < n.size();i++){
                num += (n[i] - '0') * w;
                w *= 10;
            }
            stk.push(num);
            n = "";
        } else if('0' <= s[i] && s[i] <= '9'){
            n += s[i];
        } else {
            int num1 = stk.top();
            stk.pop();
            int num2 = stk.top();
            stk.pop();
            if(s[i] == '+'){
                stk.push(num2 + num1);
            } else if(s[i] == '-'){
                stk.push(num2 - num1);
            } else if(s[i] == '*'){
                stk.push(num2 * num1);
            } else if(s[i] == '/'){
                stk.push(num2 / num1);
            }
        }
    }
    cout << stk.top();
    return 0;
}

不懂私信我