150. Evaluate Reverse Polish Notation (Stack)

class Solution {
public:
    int evalRPN(vector< string > &tokens) {
        stack< int > operandStack;
        int operand1;
        int operand2;
        for(int i = 0; i < tokens.size(); i++){
            if(tokens[i]=="+"){
                operand1 = operandStack.top();
                operandStack.pop();
                operand2 = operandStack.top();
                operandStack.pop();
                operand2 += operand1;
                operandStack.push(operand2);
            }
            else if(tokens[i]=="-"){
                operand1 = operandStack.top();
                operandStack.pop();
                operand2 = operandStack.top();
                operandStack.pop();
                operand2 -= operand1;
                operandStack.push(operand2);
            }
            else if(tokens[i]=="*"){
                operand1 = operandStack.top();
                operandStack.pop();
                operand2 = operandStack.top();
                operandStack.pop();
                operand2 *= operand1;
                operandStack.push(operand2);
            }
            else if(tokens[i]=="/"){
                operand1 = operandStack.top();
                operandStack.pop();
                operand2 = operandStack.top();
                operandStack.pop();
                operand2 /= operand1;
                operandStack.push(operand2);
            }
            else{
                operand1 = atoi(tokens[i].c_str());
                operandStack.push(operand1);
            }
        }
        return operandStack.top();
    }
};