P1449 后缀表达式

#include<iostream>
#include<stack>

using namespace std;

string s;
stack<int> stk;

int main(){
    cin >> s;
    
    for(int i = 0; s[i] != '@'; i ++){
        if(isdigit(s[i])){
            int p = 0;
            while(isdigit(s[i])) p = p * 10 + s[i ++] - '0';
            stk.push(p);
            continue;
        }
        if(s[i] == '.') continue;
        
        int a = stk.top();
        stk.pop();
        int b = stk.top();
        stk.pop();
        
        switch(s[i]){
            case '+' : stk.push(a + b); break;
            case '-' : stk.push(b - a); break;
            case '*' : stk.push(a * b); break;
            case '/' : stk.push(b / a); break;
        }
    }
    
    cout << stk.top() << endl;
    
    return 0;
}