Postfix Evaluation

#include<bits/stdc++.h>
using namespace std;

int T;
string s;
stack<int> st;

bool isoperator(char x){
    if(x == '+' || x == '-' || x == '*' || x == '/')
        return true;
    return false;
}

int operation(int a, int b, char op){
    if(op == '+')
        return a+b;
    if(op == '-')
        return a-b;
    if(op == '*')
        return a*b;
    if(op == '/')
        return a/b;
}

int main()
{
    cin>>T;
    while(T--){
        cin>>s;
        for(int i=0; i<s.length(); ++i){
            if(isoperator(s[i])){
                int b = st.top();
                st.pop();
                int a = st.top();
                st.pop();
                st.push(operation(a, b, s[i]));
            }
            else
                st.push(s[i] - '0');
        }
        cout<<st.top()<<endl;
        st.pop();
    }
    return 0;
}