1331：【例1-2】后缀表达式的值

后缀表达式的值

#include<iostream>
#include<cstring>
#include<stack>
using namespace std;
typedef long long ll;
ll t;
stack<ll> sta;
ll cal(ll t1,ll t2,char c){
    ll ans;
    if(c=='+')ans=t1+t2;
    else if(c=='-')ans=t2-t1;
    else if(c=='*')ans=t1*t2;
    else ans=t2/t1;
    return ans;
}
int main(){
    string s;
    while(cin>>s){
        if(s[0]>='0'&&s[0]<='9'){
            t=0;
            for(int i=0;i<s.length();i++)
                t=t*10+s[i]-'0';
            sta.push(t);
        }else{
            for(int i=0;i<s.length()-1;i++){
                ll t1=sta.top(),t2;
                sta.pop();
                t2=sta.top();
                sta.pop();
                sta.push(cal(t1,t2,s[i]));
            }
            break;
        }
    }
    cout<<sta.top();
    return 0;
}