Sometime got Compile Error, Sometime say Runtime Error //Last executed input: ["18"]

Question

I have updated the code witch now works. The method to solve this problem is: when meet a number, push it into the stack. when meet a operator(+, -, *, /), pop two number from the stack, do the math and push the result into the stack again. that's how to Evaluate Reverse Polish Notation.

#include <stack>

class Solution {
public:
    int evalRPN(vector<string> &tokens) {

        stack<int> st;
        int a, b;
        for (int i = 0; i < tokens.size(); i++){
            if (tokens[i] != "+" && tokens[i] != "-" && tokens[i] != "*" && tokens[i] != "/"){
                st.push(atoi(tokens[i].c_str()));
                continue;
            }

            b = st.top();st.pop();
            a = st.top();st.pop();
            switch(tokens[i][0]){
            case '+':
                st.push(a+b);break;
            case '-':
                st.push(a-b);break;
            case '*':
                st.push(a*b);break;
            case '/':
                st.push(a/b);break;
            }
        }
        return st.top();
    }

};

Comments

Could you please update the post with explanation of algorithm and comments in code?

Answer 1

You should initialize the i in for (int i; i < tokens.size(); i++)

Comments

thank you very much. The code has been accepted.