using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

        public static void Main()

    {

        string str = "45.0*(6-7+6*(23+2))"; // this works

             str = "45.0*(6-7+6+9)*(23+2)"; // this doesnt 

        Console.WriteLine(Evaluate(str));

    }

​

    public static double Evaluate(string expr)

    {

        Stack<String> stack = new Stack<String>();

​

        string value = "";

        for (int i = 0; i < expr.Length; i++)

        {

            String s = expr.Substring(i, 1);

​

            char chr = s.ToCharArray()[0];

​

            if (!char.IsDigit(chr) && chr != '.' && value != "")

            {

                stack.Push(value);

                value = "";

            }

            if (s.Equals("("))

            {

                string innerExp = "";

                i++; //Fetch Next Character

                int bracketCount = 0;

                for (; i < expr.Length; i++)

                {

                    s = expr.Substring(i, 1);

​

                    if (s.Equals("(")) bracketCount++;

​

                    if (s.Equals(")"))

                    {

                        if (bracketCount == 0) break;

                        bracketCount--;

                    }

                    innerExp += s;

                }

                stack.Push(Evaluate(innerExp).ToString());

            }

            else if (s.Equals("+") ||

                     s.Equals("-") ||

                     s.Equals("*") ||

                     s.Equals("/"))

            {

                stack.Push(s);

            }

            else if (char.IsDigit(chr) || chr == '.')

            {

                value += s;

​

                if (value.Split('.').Length > 2)

                    throw new Exception("Invalid decimal.");

​

                if (i == (expr.Length - 1))

                    stack.Push(value);

​

            }

            else

            {

                throw new Exception("Invalid character.");

            }

​

        }

        List<String> list = stack.ToList<String>();

        for (int i = list.Count - 2; i >= 0; i--)

        {

            if (list[i] == "/")

            {

                list[i] = (Convert.ToDouble(list[i - 1]) / Convert.ToDouble(list[i + 1])).ToString();

                list.RemoveAt(i + 1);

                list.RemoveAt(i - 1);

                i -= 2;

            }

        }

​

        for (int i = list.Count - 2; i >= 0; i--)

        {

            if (list[i] == "*")

            {

                list[i] = (Convert.ToDouble(list[i - 1]) * Convert.ToDouble(list[i + 1])).ToString();

                list.RemoveAt(i + 1);

                list.RemoveAt(i - 1);

                i -= 2;

            }

        }

        for (int i = list.Count - 2; i >= 0; i--)

        {

            if (list[i] == "+")

            {

                list[i] = (Convert.ToDouble(list[i - 1]) + Convert.ToDouble(list[i + 1])).ToString();

                list.RemoveAt(i + 1);

                list.RemoveAt(i - 1);

                i -= 2;

            }

        }

        for (int i = list.Count - 2; i >= 0; i--)

        {

            if (list[i] == "-")

            {

                list[i] = (Convert.ToDouble(list[i - 1]) - Convert.ToDouble(list[i + 1])).ToString();

                list.RemoveAt(i + 1);

                list.RemoveAt(i - 1);

                i -= 2;

            }

        }

        stack.Clear();

        for (int i = 0; i < list.Count; i++)

        {

            stack.Push(list[i]);

        }

​

        return Convert.ToDouble(stack.Pop());

    }

​

    }