using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ExpressionEvaluation
{
    class Program
    {
        static string expression = "(2.2 * 3 + 2)*5-(3*4)/4"; // Insert an (correct) expression to evaluate, for example: (600-500+2)/2

        static Stack<char> stOperator = new Stack<char>();
        static Stack<double> stOperand = new Stack<double>();

        static void Main(string[] args)
        {
            expression = expression.Replace(" ", String.Empty).Replace(",", ".");

            EvaluateExpression(expression);

            Console.WriteLine($"Input:  {expression}");
            Console.WriteLine($"Output: {((stOperand.Count==1)?(stOperand.Pop()).ToString().Replace(",", "."):"ERROR!")}");
        }

        static void EvaluateExpression(string e)
        {
            string number = String.Empty;

            for (int i = 0; i < e.Length; i++)
            {
                char c = e[i];

                if (c == '+' || c == '-' || c == '*' || c == '/' || c == '(' || c == ')')
                {
                    if (number != String.Empty) { stOperand.Push(Parse(number)); number = String.Empty; }

                    if (c == ')')
                    {
                        while (stOperator.Count > 0 && stOperator.Peek() != '(')
                        {
                            EvaluateNext();
                        }

                        stOperator.Pop();

                        continue;
                    }

                    if (stOperator.Count > 0)
                    {
                        if ((stOperator.Peek() == '*' || stOperator.Peek() == '/') && c != '(') EvaluateNext();
                    }

                    stOperator.Push(c);

                    continue;
                }

                number += c.ToString();
            }

            if (number != String.Empty) { stOperand.Push(Parse(number)); number = String.Empty; }

            while (stOperator.Count > 0)
            {
                EvaluateNext();
            }
        }

        static void EvaluateNext()
        {
            char o = stOperator.Pop();

            double b = stOperand.Pop();
            double a = stOperand.Pop();

            if (stOperator.Count > 0)
            {
                if (stOperator.Peek() == '-' && o != '*' && o != '/') b = -b;
            }

            switch (o)
            {
                case '+':
                    stOperand.Push(a + b);
                    break;
                case '-':
                    stOperand.Push(a - b);
                    break;
                case '*':
                    stOperand.Push(a * b);
                    break;
                case '/':
                    stOperand.Push(a / b);
                    break;
            }
        }

        static double Parse(string number)
        {
            return (Double.Parse(number, System.Globalization.CultureInfo.InvariantCulture));
        }
    }
}