#include <list> /* Linked Lists */
#include <stack> /* Stacks */
#include <iostream> /* cout cin */


int main() {

    std::stack< double, std::list<double> > postfixStack;
    std::string input;

    std::cout << "Enter a postfix expression: ";

    std::getline(std::cin, input);

    while (input != "") {
        std::cout << "Input expression: " << input << std::endl;
        for (int i = 0; i<input.length()-1; i++) {
            if (input.compare(i, 1, " ")) { // should ignore spaces, but doesn't
                std::cout << "Skipping element " << i << " n";
            } else if (static_cast<int>(input[i]) == input[i]) { // push numbers onto the stack
                postfixStack.push(static_cast<double>(input[i]));
                std::cout << "Pushing " << input[i] << " onto the stack.n";
            } else if (input.compare(i, 1, "+")) { // pop two numbers off the stack (1), apply the operator to them (2), and push that onto the stack (3)
                double operand1 = postfixStack.top();
                postfixStack.pop();
                double operand2 = postfixStack.top();
                postfixStack.pop();
                postfixStack.push(operand1 + operand2);
                std::cout << "Adding " << operand1 << " and " << operand2 << std::endl;
            }
        }
        std::getline(std::cin, input);
    }

    if (!postfixStack.empty()) {
        std::cout << "Result of expression: " << postfixStack.top() << std::endl;
    } else {
        std::cout << "It appears that you did not enter an expression to evaluate.n";
    }

    return 0;
}