P1449 后缀表达式

#include <bits/stdc++.h>
using namespace std;
int main(){
    int x=0,tmp,a,b;
    string s;
    stack<int> stk;
    cin>>s;
    for(int i=0;i<s.length()-1;i++){
        if(!isdigit(s[i])&&s[i]!='.'){a=stk.top();stk.pop();b=stk.top();stk.pop();}
        switch(s[i]){
            case '+':stk.push(a+b);break;
            case '-':stk.push(a-b);break;
            case '*':stk.push(a*b);break;
            case '/':stk.push(a/b);break;
            default:x=0;while(s[i]!='.')x=x*10+(s[i]-'0');stk.push(x);
        }
    }
    cout<<stk.top()<<endl;
    return 0;
}