/** @author
* @file main.cpp */

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

using namespace::std;

string infixToPostfix(string parExpression);
double evaluate(string parExpression);
int precedence(char parC);

int main()
{
    // Test the following cases
    cout << evaluate(infixToPostfix("2-9")) << endl;
    cout << evaluate(infixToPostfix("(3+2)*5")) << endl;
    cout << evaluate(infixToPostfix("(1+7)*(5/2)")) << endl;
    cout << evaluate(infixToPostfix("4+3*5/6")) << endl;
    return 0;
}


string infixToPostfix(string parExpression)
{
    stack<char> theStack;
    string postFixExpression = "";
    for (unsigned int c = 0; c < parExpression.length(); c++)
    {
        switch (parExpression[c])
        {
        case '0':
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9':
            postFixExpression = postFixExpression + parExpression[c];
            break;
        case '(':
            theStack.push(c);
            break;
        case '+':
        case '-':
        case '*':
        case '/':
            while ((!theStack.empty()) && (theStack.top() != '(') && (precedence(c) <= precedence(theStack.top())))
            {
                postFixExpression = postFixExpression + theStack.top();
                theStack.pop();
            }
            theStack.push(c);
            break;
        case ')':
            while (theStack.top() != '(')
            {
                postFixExpression = postFixExpression + theStack.top();
                theStack.pop();
            }
            theStack.pop();
            break;
        }

    }

    while (!theStack.empty())
    {
        postFixExpression = postFixExpression + theStack.top();
        theStack.pop();
    }
    return postFixExpression;
}

double evaluate(string parExpression)
{
    stack<double> theStack;
    double result = 0;
    double operand1, operand2;
    for (unsigned int x = 0; x < parExpression.length(); x++)
    {
        if (isdigit(x))
        {
            theStack.push(x);
        }
        else
        {
            operand2 = (double)theStack.top();
            theStack.pop();
            operand1 = (double)theStack.top();
            theStack.pop();
            switch (parExpression[x])
            {
            case '+':
                result = operand1 + operand2;
                theStack.push(result);
                break;
            case '-':
                result = operand1 - operand2;
                theStack.push(result);
                break;
            case '*':
                result = operand1 * operand2;
                theStack.push(result);
                break;
            case '/':
                result = operand1 / operand2;
                theStack.push(result);
                break;
            }


        }
    }
    return theStack.top();
}

int precedence(char parC)
{
    if ((parC == '*') || (parC == '/'))
        return 1;
    else
        return 0;

}