// infix expression evaluation
// implemented with STL vector
// evalues expression with multiple digit numbers, * / + - and {} [] () paratheis
// assume the expression is well formatted with balanced braces.

#include <iostream>
#include <stack>
#include <string>

using namespace std;

//----------------------------------------------------------------
// Generates a stack of string tokens representing postfix
// notation for the input line
void generateRPN(string line, stack<string> &postfix);

//----------------------------------------------------------------
// Returns a the result of evaluating the passed postfix token
// stack as a decimal string
string evaluateRPN(stack<string> &postfix)
{
    //this is going to be the reversed stack just to make it numbers first then operands later
    stack<string> reversedStack;

    // just going to push starting from the top of postfix stack
    int number1 = 0;
    int number2 = 0;
    int smallAnswer = 0;
    string ssmallAnswer;

    while (!postfix.empty()) {
        reversedStack.push(postfix.top());
        postfix.pop();
    }

    stack<string> numbersStack;

    while (!reversedStack.empty()) {
        if (isdigit(reversedStack.top()[0])) {
            numbersStack.push(reversedStack.top());
            reversedStack.pop();
        } else {
            if (reversedStack.top() == "-") {
                number2 = stoi(numbersStack.top());
                numbersStack.pop();
                number1 = stoi(numbersStack.top());
                numbersStack.pop();
                smallAnswer = number1 - number2;
                numbersStack.push(to_string(smallAnswer));
            } else if (reversedStack.top() == "+") {
                number2 = stoi(numbersStack.top());
                numbersStack.pop();
                number1 = stoi(numbersStack.top());
                numbersStack.pop();
                smallAnswer = number1 + number2;
                numbersStack.push(to_string(smallAnswer));
            } else if (reversedStack.top() == "*") {
                number2 = stoi(numbersStack.top());
                numbersStack.pop();
                number1 = stoi(numbersStack.top());
                numbersStack.pop();
                smallAnswer = number1 * number2;
                numbersStack.push(to_string(smallAnswer));
            } else { // (reversedStack.top() == "/")
                number2 = stoi(numbersStack.top());
                numbersStack.pop();
                number1 = stoi(numbersStack.top());
                numbersStack.pop();
                smallAnswer = number1 / number2;
                numbersStack.push(to_string(smallAnswer));
            }
            reversedStack.pop();
        }
    }
    return 0;

}

//----------------------------------------------------------------
int main(int argc, char ** argv)
{
    string line;
    cout << "Expression: ";
    while ( getline(cin, line) )
    {
        // skip empty line
        if (line.length() == 0)
            continue;

        // Makes line lowercase for checking to be case insensitive
        //transform(line.begin(), line.end(), line.begin(), ::toupper);

        // exits program if 'exit' is entered



        stack<string> postfix;

        generateRPN(line, postfix);

        cout << "Answer: " << evaluateRPN(postfix) << endl;
        line.clear();
        cout << "Expression: ";
    }
    return 0;
}